Pump device and hydraulic circuit system for construction machinery

Abstract

In a hydraulic circuit system and the pump device that use a tandem pump having arranged two hydraulic pumps that can independently control the flow rates of a plurality of delivery ports and use a plurality of selector valves, it is made possible to enhance the operability and to enhance the mountability of a pump device by a size reduction and a reduction in hydraulic hoses. To this end, first and second hydraulic pumps 11 and 12 that include four pump elements 11a to 11d and 12a to 12d that can independently control flow rates of hydraulic fluid delivered from delivery ports 45a to 45d and 46a to 46d, and are spaced in the axial direction of a shaft 14 to provide a tandem pump 30 have a port block 13 configured as a shared part and forming openings of the delivery ports 45a to 45d and 46a to 46d at a block surface 13S of the port block 13, and a block surface 13S of the port block 13 is coupled with a manifold block 40 mounting selector valves 41a to 41d and 42a to 42d and having service ports 43 and 44 formed therein.

Description

Technical Field

[0001] The present invention relates to a hydraulic circuit system for a construction machine that incorporates a pump device capable of controlling the flow rates of a plurality of delivery ports independently, and the pump device.Background Art

[0002] Patent Document 1 describes, as a pump device for use in a hydraulic circuit system for a construction machine, typically a hydraulic excavator, a pump device called a tandem pump including two pumps, i.e., a front pump and a rear pump, spaced in the axial direction (i.e., disposed in tandem). Each of the front pump and the rear pump of the tandem pump is configured as a two-flow type piston pump that produces two delivery flow rates. In addition, a port block may be interposed between the front pump and the rear pump, and have four delivery ports separated into two pairs that are open at different side faces of the port block, to thereby provide four delivery flow rates.

[0003] Patent Document 2 described a hydraulic circuit system including a hydraulic pump capable of controlling the flow rates of four delivery ports independently. The four delivery ports are connected to four load port lines through sixteen directional control valves. The directional control valves are switched to connect the delivery ports the number of which is required by an actuator to the corresponding load port lines to enable hydraulic fluid to be supplied to the actuator at a required flow rate.Prior Art DocumentPatent Documents

[0004] Patent Document 1: Japanese patent 5027878 Patent Document 2: U.S. 2019 / 0211849A1 Summary of the InventionProblems to be Solved by the Invention

[0005] The tandem pump described in Patent Document 1 has the four delivery ports separated into the two pairs that are open at the different side faces of the port block disposed between the front pump and the rear pump, thereby providing four delivery flow rates. This reduces the port block in size to reduce the overall size of the tandem pump. However, each of the front pump and the rear pump is a pump called a split-flow pump having two delivery ports, which is unable to control its two delivery flow rates independently of each other.

[0006] The hydraulic circuit system described in Patent Document 2 is able to provide four delivery flow rates from the single pump and to control the four delivery flow rates independently of each other. Moreover, the directional control valves are switched as required by the actuator to change the number of delivery ports connected to the actuator, thereby enabling the actuator to be supplied with hydraulic fluid at a required flow rate.

[0007] However, in the hydraulic circuit system described in Patent Document 2, inasmuch as the single pump has the four delivery ports and the four delivery flow rates are provided from the four delivery ports, it is necessary to connect the four delivery ports, with four hydraulic hoses, to a directional control valve including sixteen directional control valves. Consequently, the pump is large in size and the hose layout is complex, causing the hydraulic circuit system to face the problem that the pump has poor mountability on construction machines.

[0008] The problem manifests itself particularly when attempts are made to increase the number of pumps (delivery ports) for enhancing operability.

[0009] Specifically, construction machines having a plurality of actuators to be driven, such as hydraulic excavators, are required to increase the number of pumps (delivery ports) connected to the actuators in order to enhance the operability when the actuators are driven. To meet the requirements, it is preferable to use a plurality of hydraulic pumps capable of independently controlling the flow rates of a plurality of delivery ports as described in Patent Document 2. For example, if two hydraulic pumps are used as a tandem pump, since the number of delivery ports whose flow rates can be independently controlled is increased to eight, the number of delivery ports required for the actuators can be finely adjusted and fluctuations in the speed of the actuator are made smooth when the number of delivery ports is switched. As a result, the operability when the actuators are driven is enhanced.

[0010] However, for example, providing two of the hydraulic pump described in Patent Document 2 are disposed in tandem, since the number of delivery ports increases to eight and the number of hydraulic hoses that connect the eight delivery ports to directional control valves also increases to eight, the hydraulic pressure source (pump device) is large in size and the hose layout is complex, with the result that the pump device has its mountability greatly lowered.

[0011] An object of the present invention is to provide a hydraulic circuit system and a pump device for a construction machine, which use a tandem pump having arranged two hydraulic pumps that can independently control the flow rates of a plurality of delivery ports and use a plurality of selector valves, it is thereby made possible to enhance the operability when the actuators are driven and to enhance the mountability of a pump device by a size reduction and a reduction in hydraulic hoses.Means for Solving the Problems

[0012] In order to achieve the above object, there is provided, in accordance with the present invention, a hydraulic circuit system for a construction machine, the hydraulic circuit system including: a prime mover; a pump device driven by the prime mover; a plurality of actuators driven by hydraulic fluid delivered from the pump device; and a plurality of directional control valves that control flows of the hydraulic fluid supplied from the pump device to the plurality of actuators, the pump device including a tandem pump having first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by the prime mover, in which the hydraulic circuit system further includes a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open, and the plurality of service ports of the manifold block are connected, through a plurality of conduits, to a control valve having a valve housing that contains the plurality of directional control valves.

[0013] In order to achieve the above object, there is also provided, in accordance with the present invention, a pump device for a construction machine, the pump device including: a tandem pump including first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by a prime mover, in which the pump device further includes a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein, and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps, and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, and the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open.

[0014] According to the present invention, the two hydraulic pumps including the first hydraulic pump and the second hydraulic pump configure the tandem pump, and the first hydraulic pump and the second hydraulic pump includes, respectively, the plurality of first pump elements that can independently control flow of the hydraulic fluid delivered from the plurality of first delivery ports and the plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from the plurality of second delivery ports. Therefore, it is possible to increase the number of the delivery ports (pump elements) of the pump device. The numbers of the delivery ports (the number of the pump elements) that are connected to the actuators can be increased or reduced depending on required flow rates, so that delivered flow rates can be finely controlled to enhance the operability when the actuators are driven.

[0015] In the pump device including the tandem pump, the first delivery ports and the second delivery ports are open at the side portion of the port block as the shared part of the first hydraulic pump and the second hydraulic pump, and the manifold block having the first and second selector valves mounted therein and having the plurality of service ports formed therein is coupled to the side portion of the port block where the first and second delivery ports are open. Consequently, no hydraulic hoses are required to connect the delivery ports of the port block to the manifold block. Therefore, the pump device is enhanced in its mountability on the construction machine because of a size reduction of the pump device and a reduction in hydraulic hoses.Advantages of the Invention

[0016] According to the present invention, in a pump device and a hydraulic circuit system that use a tandem pump having arranged two hydraulic pumps that can independently control the flow rates of a plurality of delivery ports and use a plurality of selector valves, it is thereby made possible to enhance the operability when the actuators are driven and to enhance the mountability of a pump device on a construction machine by a size reduction and a reduction in hydraulic hoses.Brief Description of the Drawings

[0017] [Fig. 1] Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to a first embodiment of the present invention. [Fig. 2] Fig. 2 is a diagram illustrating a circuit configuration of the hydraulic circuit system according to the first embodiment of the present invention. [Fig. 3] Fig. 3 is a longitudinal cross-sectional view of a pump device along its shaft. [Fig. 4] Fig. 4 is a longitudinal cross-sectional view of the pump device along line A-A of Fig. 3. [Fig. 5] Fig. 5 is a plan view, partly in cross section, of the pump device. [Fig. 6] Fig. 6 is a plan view of the pump device along line B-B of Fig. 3. [Fig. 7] Fig. 7 is a view illustrating part of an electronically controlled hydraulic pump including pump elements, the view being explanatory of operating principles of first and second hydraulic pumps. Modes for Carrying Out the Invention

[0018] An embodiment of the present invention will be described in detail below with reference to the drawings.<First Embodiments

[0019] A first embodiment of the present invention will be described below.~Construction machine-

[0020] Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to the first embodiment of the present invention.

[0021] A hydraulic excavator 100 depicted in Fig. 1 includes a lower track structure 101 having left and right crawler-type track devices 108a and 108b, and an upper swing structure 102 mounted on the lower track structure 101 through a swing device 107 and having a cabin 102a to be occupied by an operator.

[0022] The hydraulic excavator 100 also includes a front work implement 103 having a boom 104 connected to a front portion of the upper swing structure 102. The boom 104 is driven by a boom cylinder 1 as a single-rod hydraulic cylinder 1. An arm 105 is connected to the distal end of the boom 104. The arm 105 is driven by an arm cylinder 2. The arm 105 has a distal end connected to a bucket 106 as a work tool. The bucket 106 is driven by a bucket cylinder 3 as a work tool cylinder. The swing device 107 is driven by a swing motor 4, and the track devices 108a and 108b are driven, respectively, by left and right track motors 5a and 5b.-Hydraulic circuit system-

[0023] Fig. 2 is a diagram illustrating a circuit configuration of the hydraulic circuit system according to the first embodiment of the present invention.

[0024] As illustrated in Fig. 2, the hydraulic circuit system includes an engine 9 as a prime mover, a pump device 10 driven by the engine 9, a plurality of actuators 1 through 5b (see Fig. 5 for the actuators 3 through 5b) driven by hydraulic fluid delivered from the pump device 10, a plurality of directional control valves 21 through 29 for controlling flows of the hydraulic fluid supplied from the pump device 10 to the actuators 1 through 5b, and a plurality of control lever devices 56a, 56b, 56c, and 56d for switching the directional control valves 21 through 29 to operate the actuators 1 through 5b.

[0025] The pump device 10 includes a tandem pump 30 having first and second hydraulic pumps 11 and 12 spaced in an axial direction of a shaft 14 driven and rotated by the engine 9, and a manifold block 40 having four first selector valves 41a through 41d mounted therein as a plurality of first selector valves and four second selector valves 42a through 42d mounted therein as a plurality of second selector valves, and having two first and second service ports 43 and 44 formed therein as a plurality of service ports. The first and second hydraulic pumps 11 and 12 are driven by the engine 9 to introduce the hydraulic fluid from a tank 55 and deliver the hydraulic fluid. The engine 9 may be replaced with an electrically driven motor.

[0026] The first and second hydraulic pumps 11 and 12 have four first delivery ports 45a through 45d as a plurality of first delivery ports and four second delivery ports 46a through 46d as a plurality of second delivery ports, respectively. The first hydraulic pump 11 includes four pump elements 11a through 11d as a plurality of first pump elements that can independently control the hydraulic fluid delivered from the four first delivery ports 45a through 45d. The second hydraulic pump 12 includes four pump elements 12a through 12d as a plurality of second pump elements that can independently control the hydraulic fluid delivered from the four second delivery ports 46a through 46d. Details of the "pump elements" will be described in detail later.

[0027] The manifold block 40 is configured to switch the directions of flows of the hydraulic fluid from the first and second delivery ports 45a through 45d and 46a through 46d with use of the first and second selector valves 41a through 41d and 42a through 42d so as to introduce the hydraulic fluid into either one of the first and second service ports 43 and 44.

[0028] The first and second selector valves 41a through 41d and 42a through 42d are solenoid selector valves that can be switched between a first position that is an initial position and a second position that is a non-initial position. When the first selector valves 41a through 41d are at the first position, they establish communication between the first delivery ports 45a through 45d and the first service port 43. When the first selector valves 41a through 41d are at the second position, they establish communication between the first delivery ports 45a through 45d and the second service port 44. When the second selector valves 42a through 42d are at the first position, they establish communication between the second delivery ports 46a through 46d and the second service port 44. When the second selector valves 42a through 42d are at the second position, they establish communication between the second delivery ports 46a through 46d and the first service port 43.

[0029] The first and second service ports 43 and 44 of the manifold block 40 are connected via respective first and second conduits 51 and 52 to a control valve 20 that houses the directional control valves 21 through 29 in its valve housing.

[0030] The actuators 1 through 5b are the boom cylinder 1, the arm cylinder 2, the bucket cylinder 3, the swing motor 4, the left track motor 5a, and the right track motor 5b, respectively. The directional control valves 21 through 29 are a right track directional control valve 21, a bucket directional control valve 22, a boom I directional control valve 23, a boom directional control valve 27, a swing directional control valve 25, an arm I directional control valve 26, an arm II directional control valve 24, a backup directional control valve 28, and a left track directional control valve 29, respectively.

[0031] The control lever device 56a is used to control the boom 104 and the bucket 106. The control lever device 56b is used to control the arm 105 and the swing device 107. The control lever device 56c is used to control the left track device 108a. The control lever device 56d is used to control the right track device 108b.

[0032] The directional control valves 21 through 29 in the control valve 20 are divided into a first valve group 33 that includes the boom I directional control valve 23 and the boom II directional control valve 27 as directional control valves for a first particular actuator that is operated with relatively high frequency, and a second valve group 34 that includes the arm I directional control valve 26 and the arm II directional control valve 24 as directional control valves for a second particular actuator that is operated with relatively high frequency. The control valve 20 has first and second pump ports 31 and 32 connected respectively to the first and second valve groups 33 and 34. The first and second pump ports 31 and 32 are connected respectively to the first and second service ports 43 and 44 through the respective conduits 51 and 52. The number of the first and second service ports 43 and 44 and the number of the first and second pump ports are two each, identical to the number of the hydraulic pumps 11 and 12 of the tandem pump 30.

[0033] The hydraulic fluid from the first service port 43 flows through the first conduit 51 and the pump port 31 into the control valve 20 where the hydraulic fluid is supplied to the right track directional control valve 21, the bucket directional control valve 22, the boom I directional control valve 23, and the boom II directional control valve 27 of the first valve group 33. The hydraulic fluid from the second service port 44 flows through the second conduit 52 and the pump port 32 into the control valve 20 where the hydraulic fluid is supplied to the swing directional control valve 25, the arm I directional control valve 26, the arm II directional control valve 24, the backup directional control valve 28, and the left track directional control valve 29 of the second valve group 34.

[0034] The first valve group 33 is configured as an open center circuit in which the directional control valves 21, 22, 23, and 27 share a center bypass line 33a and are connected in parallel to each other, whereas the second valve group 34 is configured as an open center circuit in which the directional control valves 24, 25, 26, 28, and 29 share a center bypass line 34a and are connected in parallel to each other.

[0035] When the control lever devices 56a, 56b, 56c, and 56d have their levers not operated and there is no command from a controller 57, the directional control valves 21 through 29 are at a neutral position, with the flows of the hydraulic fluid from the pump port 32 going back to the tank 55 via the center bypass lines 33a and 34a. When the control lever devices 56a, 56b, 56c, and 56d have their levers operated and the controller 57 generates a command, the directional control valves 21 through 29 are switched from the neutral position to adjust the distribution of the flow rates of the flows of the hydraulic fluid from the pump ports 31 and 32 and supply the adjusted flows of the hydraulic fluid to the actuators 1 through 5b. When the boom I directional control valve 23 and the boom II directional control valve 27 are switched from the neutral position, the flows of the hydraulic fluid from these directional control valves 23 and 27 are merged together and supplied to the boom cylinder 1. When the arm I directional control valve 26 and the arm II directional control valve 24 are also switched from the neutral position, the flows of the hydraulic fluid from these directional control valves 24 and 26 are merged together and supplied to the arm cylinder 2.

[0036] The controller 57 is supplied with control signals input from the control lever devices 56a through 56d and sensor signals representing the rotational speed of the engine 9 and various pressures including the delivery pressures of the first and second hydraulic pumps 11 and 12. Then, the controller 57 generates and applies commands to pump controllers 58 and 59, the selector valves 41a through 41d and 42a through 42d, and the control valve 20. In response to commands from the controller 57, the pump controllers 58 and 59 control the delivery flow rates of the first and second pump elements 11a through 11d and 12a through 12d.

[0037] The rotational speed of the engine 9 may be sensed by a rotation sensor such as an encoder disposed with respect to the shaft 14 in the first hydraulic pump 11 or the second hydraulic pumps 12, for example. The delivery pressures of the first and second hydraulic pumps 11 and 12 may be sensed by pressure sensors connected to the conduits 51 and 52, for example. A sensor signal from the rotation sensor is used to control the flow rates of the hydraulic fluid from the first and second pump elements 11a through 11d and 12a through 12d, and sensor signals from the pressure sensors are used to control the horsepower of the hydraulic fluid from the first and second pump elements 11a through 11d and 12a through 12d.-Operation-

[0038] Next, an example of operation for operating the boom 104 and the arm 105 with the configuration described above will be described below.

[0039] As illustrated in Fig. 2, when the levers of the control lever devices 56a, 56b, 56c, and 56d are not operated and there is no command from the controller 57, the first and second selector valves 41a through 41d and 42a through 42d are at the illustrated position, connecting the four pump elements 11a through 11d in the first hydraulic pump 11 to the first valve group 33, and connecting the four pump elements 12a through 12d in the second hydraulic pump 12 to the second valve group 34. In addition, the delivery flow rates of the first and second pump elements 11a through 11d and 12a through 12d are either nil or insignificant. As the directional control valves 21 through 29 are at the neutral position, the hydraulic fluid therefrom flows through the center bypass lines 33a and 34a to the tank 55.

[0040] When the lever of the control lever device 56a is operated in a boom driving direction, the controller 57 issues a command to shift the boom I directional control valve 23 and the boom II directional control valve 27 depending on the lever operation amount (a required flow rate), causing the hydraulic fluid from the first hydraulic pump 11 to drive the boom cylinder 1. As the pump controller 58 issues a command to increase the flow rate of the first hydraulic pump 11, the flow rate of the first hydraulic pump 11 increases depending on the lever operation amount. First, the delivery flow rate of the pump element 11a starts to increase. When the delivery flow rate of the pump element 11a reaches a maximum flow rate, then the delivery flow rate of the pump element 11b increases. When the delivery flow rate of the pump element 11b reaches a maximum flow rate, the delivery flow rate of the pump element 11c increases. When the delivery flow rate of the pump element 11c reaches a maximum flow rate, the delivery flow rate of the pump element 11d increases. If the lever operation amount further increases until only the first hydraulic pump 11 is unable to supply the boom cylinder 1 with the required flow rate, then the second selector valve 42a is switched to add the delivery flow rate of the pump element 12a. If the selector valves 42a, 42b, 42c, and 42d are switched, the entire flow rate of the second hydraulic pump 12 can be added. Specifically, all the eight pump elements 11a through 11d and 12a through 12d can be connected to the boom cylinder 1, making it possible for the boom cylinder 1 to operate at a higher speed.

[0041] When the lever of the control lever device 56b is operated in an arm driving direction, the controller 57 issues a command to shift the arm I directional control valve 26 and the arm II directional control valve 24 depending on the lever operation amount, causing the hydraulic fluid from the second hydraulic pump 12 to drive the arm cylinder 2. As the pump controller 59 issues a command to increase the flow rate of the second hydraulic pump 12, the flow rate of the second hydraulic pump 12 increases depending on the lever operation amount. First, the delivery flow rate of the pump element 12d starts to increase. When the delivery flow rate of the pump element 12d reaches a maximum flow rate, the delivery flow rate of the pump element 12c increases. When the delivery flow rate of the pump element 12c reaches a maximum flow rate, the delivery flow rate of the pump element 12b increases. When the pump element 12b reaches a maximum flow rate, the delivery flow rate of the pump element 12c increases. If the lever operation amount further increases until only the second hydraulic pump 12 is unable to supply the arm cylinder 2 with the required flow rate, then the first selector valve 41d is switched to add the flow rate of the pump element 11d. If the selector valves 41d, 41c, 41b, and 41a are switched, the entire flow rate of the first hydraulic pump 11 can be added. Specifically, all the eight pump elements 11a through 11d and 12a through 12d can be connected to the arm cylinder 2, making it possible for the arm cylinder 2 to operate at a higher speed.

[0042] For simultaneously operating the boom 104 and the arm 105, the lever of the control lever device 56a is operated in the boom driving direction, and the lever of the control lever device 56b is operated in the arm driving direction. Then, the controller 57 issues commands to shift the boom I directional control valve 23 and the boom II directional control valve 27, and also to shift the arm I directional control valve 26 and the arm II directional control valve 24 depending on the lever operation amount (required flow rates). At this time, if the lever of the control lever device 56a is operated by 20% of its maximum operation amount and the lever of the control lever device 56b is operated by 20% of its maximum operation amount, then the pump elements 11a and 11b and the pump elements 12d and 12c deliver the hydraulic fluid, and the boom cylinder 1 is driven by the hydraulic fluid from the pump elements 11a and 11b and the arm cylinder 2 is driven by the hydraulic fluid from the pump elements 12d and 12c. If the control lever devices 56a and 56b input demands in excess of the total maximum flow rate of all the eight pump elements 11a through 11d and 12a through 12d, e.g., if the lever of the control lever device 56a is operated by 100% of its maximum operation amount and the lever of the control lever device 56b is operated by 60% of its maximum operation amount, then the pump elements 11a through 11d and 12a through 12d are distributed depending on the ratio of the operation amounts (100:60 → 5:3), and the boom cylinder 1 is driven by the five pump elements 11a, 11b, 11c, 11d, and 12a, and the arm cylinder 2 is driven by the three pump elements 12d, 12c, and 12b.

[0043] Thus, since the boom cylinder 1 and the arm cylinder 2 are driven independently of each other without the hydraulic fluid from each of the pump elements being divided, the pump elements may supply the hydraulic fluid at the flow rate under the lowest pressure required for the boom cylinder 1 and the arm cylinder 2. Accordingly, the directional control valves are not required to reduce the fluid pressure by constricting the hydraulic fluid, thereby reducing a fluid division loss.~Principles of operation of the first and second hydraulic pumps~

[0044] Each of the first pump elements 11a through 11d and the second pump elements 12a through 12d of the first and second hydraulic pumps 11 and 12 includes a plurality of cylinder working chambers and solenoid valves for changing their net displacements (capacities). On the basis of commands issued from the controller 57 and the pump controllers 58 and 59, the solenoid valves are switched to change the net volumes of the cylinder working chambers, to thereby control the delivery flow rates of the first pump elements 11a through 11d and the second pump elements 12a through 12d. A hydraulic pump that incorporates such pump elements may occasionally be referred to as a digital pump.

[0045] The principles of operation of the first hydraulic pump 11 and the second hydraulic pump 12 will be described in detail below with reference to Fig. 7. Fig. 7 is a schematic view illustrating part of an electronically controlled hydraulic pump 200 including a plurality of pump elements. Each of the first and second hydraulic pumps 11 and 12 has configuration equivalent to the hydraulic pump 200.

[0046] The hydraulic pump 200 has a pump shaft 204 and at least three cylinder working chambers (hereinafter simply referred to as "working chambers") 202 whose volumes are cyclically varied with rotation of the pump shaft 204.

[0047] The hydraulic pump 200 also has low-pressure valves 209 which regulate the flow of hydraulic fluid between a low-pressure manifold 201 communicating with a tank port 216 and the working chambers 202, and high-pressure valves 212 which reguate the flow of the hydraulic fluid between a high-pressure manifold 213 communicating with a delivery port 214 and the working chambers 202.

[0048] The hydraulic pump 200 forms a plurality of pump elements made with the working chambers 202. Each of the pump elements has one or more of the working chambers 202 (typically a plurality of working chambers 202) and is connected to the high-pressure manifold 213 that is common to the plurality of working chambers 202 in the pump elements.

[0049] A controller 207 corresponds to the pump controllers 58 and 59 illustrated in Fig. 2. The controller 207 is configured to actively control at least the low-pressure valves of the working chambers 202 in phased relationship with cycles of working chamber volume to determine whether each working chamber 202 undergoes either an active cycle, with a net displacement of hydraulic fluid between the low-pressure manifold 210 and the high-pressure manifold 213, or an inactive cycle, with no net displacement of hydraulic fluid between the low-pressure manifold 210 and the high-pressure manifold 213, for each cycle of working chamber volume, such that the net displacement of the working chambers 202 of each pump element is controlled in response to a respective demand for hydraulic fluid.

[0050] The hydraulic pump 200 includes a plurality of cylinders 201 which has the working chambers 202 defined by the inner surface of the cylinder 201 and a plurality of pistons 203 driven by an eccentric cam 205 mounted to the pump shaft 204, and which reciprocates within the respective cylinders 201 to cyclically vary the volumes of the working chambers 202 in the cylinders 201. The hydraulic pump 200 further includes a sensor 206 for sensing the angular position and / or the rotational speed of the shaft 204. Information sensed by the sensor 206 is delivered through a signal line 208 to the controller 207, which enables the controller 207 to determine the instantaneous phase of the cycle of each working chamber 202 on the basis of the sensed information.

[0051] Each of the working chambers 202 is associated with the low-pressure valve (LPV) 209 configured as an electronically operated face-sealing poppet valve. The LPV 209 is operable to selectively seal off a channel extending from the working chamber 202 to the low-pressure manifold 210, which may connect one or several working chambers 202, or indeed all of the working chambers 202 in the pump element, to the tank port 216.

[0052] The LPV 209 is a normally open solenoid actuated valve. During an intake stroke in which the pressure within the working chamber 202 is less than or equal to the pressure within the low-pressure manifold 210, the LPV 209 opens passively to bring fluid communication the working chamber 202 with the low-pressure manifold 210, but the LVP 209 is connected to the controller 207 by an LPV control line 211 and selectively closable under active control of the controller 207 to bring the working chamber 202 out of fluid communication with the low-pressure manifold 210. The LPV 209 may alternatively be a normally closed solenoid valve.

[0053] Each of the working chambers 202 is also associated with the high-pressure valve (HPV) 212 in the form of a pressure actuated delivery valve. The HPV 212 opens outwards from the working chamber 202 and is operable to seal off a fluid from the working chamber 202 to the high-pressure manifold 213. When the HPV 212 opens, the high-pressure manifold 213 connects the working chamber 202 to the delivery port 214, allowing the hydraulic fluid to flow from the working chamber 202 to the delivery port 214. The HPV 212 functions as a normally closed pressure-opening check valve that opens passively due to the pressure difference across the HPV 212 against the biasing member in the HPV 212. In some embodiments, the HPV 212 also functions as a normally closed solenoid actuated check valve which the controller 202 may selectively hold opens through HPV control lines 215 once the HPV is opened by pressure within the associated working chamber 202. Typically, the HPV 212 is not operable to open by the controller 207 against the pressure in the high-pressure manifold 213. The HPV 212 may additionally be openable under the control of the controller 207 when there is pressure in the high-pressure manifold 213 but not in the working chamber 202, or may be partially openable.

[0054] In a pumping mode, the controller 207 selects the net rate of displacement of hydraulic fluid from the working chambers 202 to the high-pressure manifold 213 by the hydraulic pump 200 by actively closing one or more of LPVs 209 typically near the point of maximum volume in the volume cycle of the associated working chambers 202, closing the path to the low-pressure manifold 210 and thereby directing the hydraulic fluid tout through the associated HPVs 212 on the subsequent contraction stroke (but does not actively hold open the HPVs 212), causing an active cycle with a net displacement of hydraulic fluid in the working chambers 202. Alternatively, the LPVs 209 may be held open throughout the entire cycles of the working chambers 202 (or the working chambers may be held sealed throughout the entire cycles of the working chambers 202), causing the inactive cycle with no net displacement of hydraulic fluid. The controller 207 selects the numbers and sequence of active and inactive cycles to produce a flow or create a shaft torque or power to satisfy a selected net rate of displacement of hydraulic fluid by the working chambers 202 of the pump elements which are connected to the same high-pressure manifold 213 and the same delivery port 214 to meet a demand for fluid flow from the pump elements.

[0055] As well as determining whether or not to close or hold open the LPVs 209 on a cycle by cycle basis to select between active and inactive cycles, the controller 207 is operable to vary the precise phasing of the closure of the LPVs 209 and / or the HPVs 212 with respect to the varying volumes of the working chambers 202 and thereby to select net rate of displacement of hydraulic fluid from the high-pressure manifold 213 to the low-pressure manifold 210 or vice versa.

[0056] Arrows depicted on the manifolds 210 and 213 indicate flow of the hydraulic fluid in a pump mode, and the flow is reversed in a motor mode.

[0057] In the illustrated example, all of the working chambers 202 are connected to the same high-pressure manifold 213 and the same delivery port 214. Typically, however, the hydraulic pump 200 further includes working chambers 202 forming one or more separate pump elements with their own respective high-pressure manifolds 213, delivery ports 214, and demanded signals.

[0058] More specifically, the first hydraulic pump 11 has four high-pressure manifolds 213 and four delivery ports 214 corresponding to the first delivery ports 45a through 45d, and the high-pressure manifolds 213 are connected to the working chambers 202 via the high-pressure valves 209. The same holds true for the second hydraulic pump 12.

[0059] The demanded signals may use any convenient units. For example, the demanded signal is expressed as "displacement fraction Fd" which is a fraction of maximum possible displacement per revolution of the pump shaft 204. Target flow rate, in volumetric terms, is expressed as the product of the volume change rate Fd and the speed of rotation of the pump shaft 204.~Structure of the pump device~

[0060] The structure of the pump device 10 according to the present embodiment will be described below.

[0061] Figs. 3 through 6 are views illustrating the structure of the pump device 10 in the hydraulic circuit system illustrated in Fig. 1. Fig. 3 is a longitudinal cross-sectional view of the pump device 10 along the shaft 14. Fig. 4 is a longitudinal cross-sectional view of the pump device 10 along line A-A of Fig. 3. Fig. 5 is a plan view, partly in cross section, of the pump device 10. Fig. 6 is a plan view of the pump device 10 along line B-B of Fig. 3.

[0062] The structure of the pump device 10 in the hydraulic circuit system according to the present embodiment will be described below with reference to Figs. 3 through 6.

[0063] In Fig. 3, as described above, the pump device 10 includes the tandem pump 30 having the first and second hydraulic pumps 11 and 12 disposed on the shaft 14 and spaced in the axial direction of the shaft 14, and the manifold block 40 mounting the first selector valves 41a through 41d and the second selector valves 42a through 42d therein (see Fig. 5) and having the two first and second service ports 43 and 44 (see Fig. 5).

[0064] The first and second hydraulic pumps 11 and 12 have a port block 13 configured as a shared part of the first and second hydraulic pumps 11 and 12. As illustrated in Fig. 6, the port block 13 has the four first delivery ports 45a through 45d and the four second delivery ports 46a through 46d that are formed to open at a side portion 13S of the port block 13. The manifold block 40 is coupled to the side portion 13S (see Figs. 3, 5, and 6) of the port block 13 where the first and second delivery ports 45a through 45d and 46a through 46d are open.

[0065] According to the illustrated embodiment, the side portion 13S of the port block 13 has a single block surface, and the first and second delivery ports 45a through 45d and 46a through 46d are open at the block surface. However, the side portion 13S of the port block 13 may have a plurality of stepped surfaces, e.g., a first surface and a second surface parallel to the first surface, and the first delivery ports 45a through 45d may be formed in the first surface whereas the second delivery ports 46a through 46d may be formed in the second surface.

[0066] The first hydraulic pump 11 has a casing 48 and two first radial piston pumps 36a and 36b disposed on a shaft 14a in the casing 48 and spaced in the axial direction of the shaft 14a. The first radial piston pump 36a provides the two first pump elements 11a and 11d among the four pump elements 11a through 11d described above, and the first radial piston pump 36b provides the remaining two first pump elements 11b and 11c.

[0067] Similarly, the second hydraulic pump 12 has a casing 49 and two second radial piston pumps 37a and 37b disposed on a shaft 14b in the casing 49 and spaced in the axial direction of the shaft 14b. The second radial piston pump 37a provides the two second pump elements 12a and 12d among the four pump elements 12a through 12d described above, and the second radial piston pump 37b provides the remaining two second pump elements 12b and 12c.

[0068] The hydraulic fluid from the tank 55 is introduced through an inlet port 47 formed in the port block 13 into a space in the casing 48 where the first radial piston pumps 36a and 36b are housed and a space in the casing 49 where the second radial piston pumps 37a and 37b are housed.

[0069] The first radial piston pump 36a is configured by main components including the shaft 14a that is part of the shaft 14, an eccentric cam 15 that rotates integrally with the shaft 14a, pistons 16 held in sliding contact with the outer circumferential surface of the eccentric cam 15, cylinders 19 in which the pistons 16 reciprocatively move, and an inlet check valve 17a and a delivery check valve 18a that establish communication with cylinder chambers 50 that are formed by the pistons 16 and the cylinders 19. Similarly, the first radial piston pump 36b is also configured by main components including the shaft 14a, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17b, and delivery check valves 18b.

[0070] Likewise, the second radial piston pump 37a is also configured by main components including a shaft 14b, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17c, and delivery check valves 18c, and the second radial piston pump 37b is also configured by main components including the shaft 14b, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17d, and delivery check valves 18d.

[0071] The shaft 14a is rotatably supported in the casing 48 and the port block 13 by bearings, and the shaft 14b is rotatably supported in the casing 49 and the port block 13 by bearings. The shafts 14a and 14b are coupled to each other by a coupling 14c, making up the shaft 14.

[0072] As illustrated in Fig. 4, the first radial piston pump 36a has six piston pumps 60 that are configured by the pistons 16 and the cylinders 19 and disposed radially outwardly at equal angular intervals on the shaft 14a. When the eccentric cam 15 that is integral with the shaft 14a rotates, the pistons 16 of the respective piston pumps 60 are reciprocatively moved in the respective cylinders 19, introducing the hydraulic fluid that has filled the space in the casing 48, from the inlet check valves 17a (see Fig. 3) into the cylinder chambers 50, and delivering the hydraulic fluid from the delivery check valves 18a. The delivered hydraulic fluid flows through inner passages 38a and 38d formed in the casing 48 and openings 39a and 39d formed in an end face of the casing 48 that faces the port block 13 into the port block 13, and is introduced therefrom into some of the first delivery ports 45a through 45d illustrated in Fig. 6, i.e., the first delivery ports 45a and 45d according to the embodiment illustrated, from which the hydraulic fluid is delivered.

[0073] Although not illustrated, the first radial piston pump 36b and the second radial piston pumps 37a and 37b are similarly configured. However, with regard to the first radial piston pump 37b, the hydraulic fluid delivered from the delivery check valves 18b is introduced into the first delivery ports 45b and 45c illustrated in Fig. 6, from which the hydraulic fluid is delivered. With regard to the first radial piston pump 37a, the hydraulic fluid delivered from the delivery check valves 18c is introduced into the second delivery ports 46a and 46d illustrated in Fig. 6, from which the hydraulic fluid is delivered. With regard to the second radial piston pump 37b, the hydraulic fluid delivered from the delivery check valves 18d is introduced into the second delivery ports 46b and 46c illustrated in Fig. 6, from which the hydraulic fluid is delivered.

[0074] As illustrated in Fig. 3, the inlet check valve 17a is a solenoid on / off valve (hereinafter referred to as "solenoid valve"). When the solenoid valve is turned off, the solenoid valve is kept open at all times by a spring as depicted at the inlet check valve 17a. The hydraulic fluid that has been introduced into the cylinder 50 upon descent of the piston 16 flows back into the casing 48 through the inlet check valve 17a when the piston 16 ascends, and is not delivered. When the solenoid valve is turned on upon ascent of the piston 16, the solenoid valve is closed as depicted at the inlet check valve 17b, pressurizing the cylinder chamber 50 to open the delivery check valve 18b from which the hydraulic fluid is delivered. By controlling the timing to turn on and off the solenoid valve, the timing to close the inlet check valve is controlled to control the delivery flow rate from the piston 16 during one stroke. Therefore, the flow rates of the piston pumps 60 can be controlled independently of each other by turning on and off the solenoid valves and controlling the timing to turn on and off the solenoid valves.

[0075] According to the present embodiment, the plurality of piston pumps 60 whose flow rates can be controlled independently are used, and a mechanism for merging and delivering the flows of the hydraulic fluid from the plurality of piston pumps 60 is referred to as "pump element."

[0076] According to the present embodiment, moreover, in order to reduce pump pulsations, one pump element uses three piston pumps 60. In the first hydraulic pump 11, the twelve piston pumps 60 of the first radial piston pumps 36a and 36b provide the four pump elements 11a through 11d, and the hydraulic fluid from the pump elements 11a through 11d is delivered from the four delivery ports 45a through 45d. Similarly, in the second hydraulic pump 12, the twelve piston pumps 60 of the second radial piston pumps 37a and 37b provide the four pump elements 12a through 12d, and the hydraulic fluid from the pump elements 12a through 12d is delivered from the four delivery ports 46a through 46d.

[0077] The above features will be further described below with reference to Fig. 4.

[0078] As illustrated in Fig. 4, the six piston pumps 60 of the first radial piston pump 36a are denoted respectively by 60a, 60b, 60c, 60d, 60e, and 60f in clockwise order. The flows of the hydraulic fluid delivered from the piston pumps 60a, 60c, and 60e are merged together to provide the pump element 11a, and the flows of the hydraulic fluid delivered from the piston pumps 60b, 60d, and 60f are merged together to provide the pump element 11d. The merged delivery flow rates flow from the openings 39a and 39d into the port block 13 from which they are introduced into the delivery ports 45a and 45d illustrated in Fig. 6. The first radial piston pump 36b of the first hydraulic pump 11 is of a similar structure. The first radial piston pump 36b provides the two pump elements 11b and 11c, and the merged delivery flow rates from the respective pump elements 11b and 11c are introduced into the delivery ports 45b and 45c illustrated in Fig. 6.

[0079] The second radial piston pumps 37a and 37b of the second hydraulic pump 12 are also of a similar structure. The second radial piston pump 37a provides the two pump elements 12a and 12d, and the merged delivery flow rates from the respective pump elements 12a and 12d are introduced into the delivery ports 46a and 46d illustrated in Fig. 6. The second radial piston pump 37b provides the two pump elements 12b and 12c, and the merged delivery flow rates from the respective pump elements 12b and 12c are introduced into the delivery ports 46b and 46c illustrated in Fig. 6.

[0080] Thus, the six piston pumps 60 of each of the two first radial piston pumps 36a and 36b are divided into two groups, and the flows of the hydraulic fluid delivered from the piston pumps 60 of each group are merged together to provide one of the four pump elements 11a through 11d of the first hydraulic pump 11. Similarly, the six piston pumps 60 of each of the two second radial piston pumps 37a and 37b are divided into two groups, and the flows of the hydraulic fluid delivered from the piston pumps 60 of each group are merged together to provide one of the four pump elements 12a through 12d of the second hydraulic pump 12.

[0081] The manifold block 40 has a block body 40a that is coupled to the side portion 13S of the port block 13 where the eight delivery ports 45a through 45d and 46a through 46d are open. As illustrated in Figs. 3 and 5, the first selector valves 41a through 41d are mounted on a side face of the block body 40a that faces the first hydraulic pump 11, and the second selector valves 42a through 42d are mounted on a side face of the block body 40a that faces the second hydraulic pump 12. The block body 40a has two passages 43a and 44a formed therein on exit sides of the first and second selector valves 41a through 41d and 42a through 42d (on upper sides of the first and second selector valves 41a through 41d and 42a through 42d as illustrated in Fig. 3). The two passages 43a and 44a extend parallel to each other as illustrated in Fig. 5 and are open at respective opposite end faces of the block body 40a. The first service port 43 is formed in the opening of the passage 43a, and the second service port 44 is formed in the opening of the passage 44a. Alternatively, the passages 43a and 44a may be open at an upper surface of the block body 40a to provide the first service port 43 and the second service port 44.

[0082] The block body 40a of the manifold block 40 has inner passages formed therein for introducing the flows of the hydraulic fluid from the eight delivery ports 45a through 45d and 46a through 46d respectively into the solenoid selector valves 41a through 41d and 42a through 42d, and inner passages formed therein for introducing the hydraulic fluid into either one of the passages 43a and 43b depending on whether or not there are commands from the controller 57 to the selector valves 41a through 41d and 42a through 42d. The inner passages provide a hydraulic circuit of the manifold block 40 as illustrated in Fig. 2.~Advantages~

[0083] The present embodiment offers the following advantages: 1. According to the present embodiment, as described above, when the boom 104 alone is to be operated, since the eight pump elements 11a through 11d and 12a through 12d are successively connected to the boom cylinder 1 depending on the lever operation amount (a required flow rate), the number of pump elements (a delivery flow rate) can be finely controlled depending on the lever operation amount, making smooth speed pulsations of the boom cylinder 1, the speed pulsations being due to the switching of the delivery ports by the selector valves 41a through 41d and 42a through 42d, and enhancing operability. Moreover, as it is possible to connect all of the eight pump elements 11a through 11d and 12a through 12d to the boom cylinder 1, the boom cylinder 1 can be operated at a high speed for performing a sufficient amount of work.

[0084] When the arm 105 alone is to be operated, the pump elements are involved in the same manner as when the boom alone is to be operated. The number of pump elements (a delivery flow rate) can be finely controlled depending on the lever operation amount, enhancing operability. Moreover, also it is possible to operate the arm cylinder 2 at a high speed, ensuring a sufficient amount of work.

[0085] If the selector valves 41a through 41d and 42a through 42d are installed at a position spaced from the pump, then eight hydraulic hoses are required to connect the delivery ports 45a through 45d and 46a through 46d to the selector valves 41a through 41d and 42a through 42d. Because the eight hydraulic hoses are connected to the delivery ports 45a through 45d and 46a through 46d, the space through which the hydraulic hoses passes tends to reduce the mountability of the pump device, and there arise many problems including an increase in the man-hours required to connect the hydraulic hoses, a leakage on account of an increased number of hydraulic joints, and a reliability risk. Furthermore, inasmuch as the delivery ports 45a through 45d and 46a through 46d need to be spaced from each other in order to connect the eight hydraulic hoses thereto, the port block 13 is liable to increase in size, making the pump device 10 itself larger in size. This also is likely to lower the mountability of the pump device 10.

[0086] According to the present embodiment, since the manifold block 40 is coupled to the side portion 13S of the port block 13 where the eight delivery ports 45a through 45d and 46a through 46d are open, no hydraulic hoses are required to connect the delivery ports 45a through 45d and 46a through 46d to the selector valves 41a through 41d and 42a through 42d. Therefore, the pump device 10 has enhanced its mountability on the construction machine because of a reduction in the size of the pump device 10 and reduced hydraulic hoses.

[0087] Furthermore, no work for connecting hydraulic hoses occurs, the pump device can be mounted with ease, and leakage locations are reduced, and thus reliability against leakage is enhanced.

[0088] According to the present embodiment, the number of the pump elements and the number of the delivery ports of the first hydraulic pump 11 and the second hydraulic pump 12 are such that the number of the pump elements 11a through 11d, the number of the pump elements 12a through 12d, the number of the delivery ports 45a through 45d, and the number of the delivery ports 46a through 46d are four each. However, these numbers are not limited to such details. The number of the pump elements and the number of the delivery ports of the first hydraulic pump 11 and the second hydraulic pump 12 may be two or more each, e.g., two, three, or five each, to achieve the advantages of the present invention with regard to operability, energy saving, and mountability.

[0089] 2. The control valve 20 is configured such that the first valve group 33 includes the boom I directional control valve 23 and the boom II directional control valve 27, and the second valve group 34 includes the arm I directional control valve 26 and the arm II directional control valve 24. Therefore, when the boom 104 and the arm 105 are to be operated in combination, the boom cylinder 1 and the arm cylinder 2 are driven independently of each other without the need to divide the hydraulic fluid supplied from the pump elements connected thereto. Accordingly, the pump elements may supply the hydraulic fluid at flow rates under minimum pressures required for the boom cylinder 1 and the arm cylinder 2. Thus, the directional control valves are not required to reduce the fluid pressure by constricting the hydraulic fluid, any fluid division loss is reduced, and energy saving is enhanced.

[0090] 3. Since the number of the service ports 43 and 44 of the manifold block 40 and the number of the pump ports 31 and 32 of the control valve 20 that are connected to each other by the conduits 51 and 52 are the same as the number (two) of the first and second hydraulic pumps 11 and 12 of the tandem pump 30, the manifold block 40 and the control valve 20 can be connected by a minimum number of hydraulic hoses. In this regard, too, the number of hydraulic hoses is reduced and the mountability on the construction machine is enhanced.

[0091] 4. The hydraulic circuit in the manifold block 40 is configured such that the first selector valves 41a through 41d establishes communication: at the first position (initial position), between the first delivery ports 45a through 45d and the first service port 43; and at the second position, between the first delivery ports 45a through 45d and the second service port 44, and such that the second selector valves 42a through 42d establishes communication: at the first position (initial position), between the second delivery ports 46a through 46d and the second service port 44; and at the second position, between the second delivery ports 46a through 46d and the first service port 43. Consequently, when the pump elements 11a through 11d are successively connected to the boom cylinder 1 depending on the lever operation amount (a required flow rate) to supply the delivery flow rates from the pump elements 11a through 11d to the boom cylinder 1, since the delivery flow rates can be supplied without the need to switch the selector valves 41a through 41d, no pressure variations occur, the pressure variations being due to the switching of the selector valves 41a through 41d, making it possible to activate or accelerate the boom cylinder 1 smoothly. This holds true also when the pump elements 42a through 42d are successively connected to the arm cylinder 2 depending on the lever operation amount (a required flow rate) to supply the delivery flow rates from the pump elements 12a through 12d to the arm cylinder 2. No pressure variations occur, the pressure variations being due to the switching of the selector valves 42a through 42d, making it possible to activate or accelerate the arm cylinder 2 smoothly.

[0092] When the eight pump elements 11a through 11d and 12a through 12d are successively connected to the boom cylinder 1 to drive the boom cylinder 1 depending on the lever operation amount, any of the selector valves 41a through 41d and 42a through 42d is not switched from the first position until only the first hydraulic pump 11 is able to supply the boom cylinder 11 with the required flow rate, and the selector valves 42a through 42d may be switched to the second position when only the first hydraulic pump 11 is unable to supply the boom cylinder 11 with the required flow rate. This holds true also when the eight pump elements 11a through 11d and 12a through 12d are successively connected to the arm cylinder 2 to drive the arm cylinder 2 depending on the lever operation amount, and the selector valves 41a through 41d may be switched to the second position when only the second hydraulic pump 12 is unable to supply the arm cylinder 2 with the required flow rate. Consequently, the number of times that the selector valves 41a through 41d and 42a through 42d are switched when the boom cylinder 1 or the arm cylinder 2 is to be driven can be reduced, resulting in enhancing the durability of the selector valves 41a through 41d and 42a through 42d.Description of Reference Characters

[0093] 1: boom cylinder (first particular actuator) 2: arm cylinder (second particular actuator) 3: bucket cylinder 4: swing motor 1 to 5b: a plurality of actuators 9: engine 10: pump device 11: first hydraulic pump 11a to 11d: first pump elements 12: second hydraulic pump 12a to 12d: second pump elements 13: port block 14: shaft 15: eccentric cam 16: piston 17a to 17d: inlet check valves 18a to 18d: delivery check valves 19: cylinder 20: control valve 21: right track directional control valve 22: bucket directional control valve 23: boom I directional control valve 24: arm II directional control valve 25: swing directional control valve 26: arm I directional control valve 27: boom 1 directional control valve 28: backup directional control valve 29: left track directional control valve 30: tandem piston 31: first pump port 32: second pump port 33: first valve group 34: second valve group 36a, 36b: first radial piston pumps 37a, 37b: second radial piston pumps 40: manifold block 41a to 41d: first selector valves 42a to 42d: second selector valves 43: first service port 44: second service port 45a to 45d: first delivery ports 46a to 46d: second delivery ports 47: inlet port 48, 49: casings 50: cylinder chamber 51: first conduit 52: second conduit 55: tank 56a, 56b, 56c, 56d: control lever devices 57: controller 58, 59: pump controllers 60a to 60f: piston pumps 100: hydraulic excavator 101: lower track structure 102: upper swing structure 108a, 108b: track device

Examples

first embodiments

[0019]A first embodiment of the present invention will be described below.

~Construction machine-

[0020]Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to the first embodiment of the present invention.

[0021]A hydraulic excavator 100 depicted in Fig. 1 includes a lower track structure 101 having left and right crawler-type track devices 108a and 108b, and an upper swing structure 102 mounted on the lower track structure 101 through a swing device 107 and having a cabin 102a to be occupied by an operator.

[0022]The hydraulic excavator 100 also includes a front work implement 103 having a boom 104 connected to a front portion of the upper swing structure 102. The boom 104 is driven by a boom cylinder 1 as a single-rod hydraulic cylinder 1. An arm 105 is connected to the distal end of the boom 104. The arm 105 is driven by an arm cylinder 2. The arm 105 has a dista...

Technical Field

[0001] The present invention relates to a hydraulic circuit system for a construction machine that incorporates a pump device capable of controlling the flow rates of a plurality of delivery ports independently, and the pump device.Background Art

[0002] Patent Document 1 describes, as a pump device for use in a hydraulic circuit system for a construction machine, typically a hydraulic excavator, a pump device called a tandem pump including two pumps, i.e., a front pump and a rear pump, spaced in the axial direction (i.e., disposed in tandem). Each of the front pump and the rear pump of the tandem pump is configured as a two-flow type piston pump that produces two delivery flow rates. In addition, a port block may be interposed between the front pump and the rear pump, and have four delivery ports separated into two pairs that are open at different side faces of the port block, to thereby provide four delivery flow rates.

[0003] Patent Document 2 described a hydraulic circuit system including a hydraulic pump capable of controlling the flow rates of four delivery ports independently. The four delivery ports are connected to four load port lines through sixteen directional control valves. The directional control valves are switched to connect the delivery ports the number of which is required by an actuator to the corresponding load port lines to enable hydraulic fluid to be supplied to the actuator at a required flow rate.Prior Art DocumentPatent Documents

[0004] Patent Document 1: Japanese patent 5027878 Patent Document 2: U.S. 2019 / 0211849A1 Summary of the InventionProblems to be Solved by the Invention

[0005] The tandem pump described in Patent Document 1 has the four delivery ports separated into the two pairs that are open at the different side faces of the port block disposed between the front pump and the rear pump, thereby providing four delivery flow rates. This reduces the port block in size to reduce the overall size of the tandem pump. However, each of the front pump and the rear pump is a pump called a split-flow pump having two delivery ports, which is unable to control its two delivery flow rates independently of each other.

[0006] The hydraulic circuit system described in Patent Document 2 is able to provide four delivery flow rates from the single pump and to control the four delivery flow rates independently of each other. Moreover, the directional control valves are switched as required by the actuator to change the number of delivery ports connected to the actuator, thereby enabling the actuator to be supplied with hydraulic fluid at a required flow rate.

[0007] However, in the hydraulic circuit system described in Patent Document 2, inasmuch as the single pump has the four delivery ports and the four delivery flow rates are provided from the four delivery ports, it is necessary to connect the four delivery ports, with four hydraulic hoses, to a directional control valve including sixteen directional control valves. Consequently, the pump is large in size and the hose layout is complex, causing the hydraulic circuit system to face the problem that the pump has poor mountability on construction machines.

[0008] The problem manifests itself particularly when attempts are made to increase the number of pumps (delivery ports) for enhancing operability.

[0009] Specifically, construction machines having a plurality of actuators to be driven, such as hydraulic excavators, are required to increase the number of pumps (delivery ports) connected to the actuators in order to enhance the operability when the actuators are driven. To meet the requirements, it is preferable to use a plurality of hydraulic pumps capable of independently controlling the flow rates of a plurality of delivery ports as described in Patent Document 2. For example, if two hydraulic pumps are used as a tandem pump, since the number of delivery ports whose flow rates can be independently controlled is increased to eight, the number of delivery ports required for the actuators can be finely adjusted and fluctuations in the speed of the actuator are made smooth when the number of delivery ports is switched. As a result, the operability when the actuators are driven is enhanced.

[0010] However, for example, providing two of the hydraulic pump described in Patent Document 2 are disposed in tandem, since the number of delivery ports increases to eight and the number of hydraulic hoses that connect the eight delivery ports to directional control valves also increases to eight, the hydraulic pressure source (pump device) is large in size and the hose layout is complex, with the result that the pump device has its mountability greatly lowered.

[0011] An object of the present invention is to provide a hydraulic circuit system and a pump device for a construction machine, which use a tandem pump having arranged two hydraulic pumps that can independently control the flow rates of a plurality of delivery ports and use a plurality of selector valves, it is thereby made possible to enhance the operability when the actuators are driven and to enhance the mountability of a pump device by a size reduction and a reduction in hydraulic hoses.Means for Solving the Problems

[0012] In order to achieve the above object, there is provided, in accordance with the present invention, a hydraulic circuit system for a construction machine, the hydraulic circuit system including: a prime mover; a pump device driven by the prime mover; a plurality of actuators driven by hydraulic fluid delivered from the pump device; and a plurality of directional control valves that control flows of the hydraulic fluid supplied from the pump device to the plurality of actuators, the pump device including a tandem pump having first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by the prime mover, in which the hydraulic circuit system further includes a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open, and the plurality of service ports of the manifold block are connected, through a plurality of conduits, to a control valve having a valve housing that contains the plurality of directional control valves.

[0013] In order to achieve the above object, there is also provided, in accordance with the present invention, a pump device for a construction machine, the pump device including: a tandem pump including first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by a prime mover, in which the pump device further includes a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein, and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps, and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, and the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open.

[0014] According to the present invention, the two hydraulic pumps including the first hydraulic pump and the second hydraulic pump configure the tandem pump, and the first hydraulic pump and the second hydraulic pump includes, respectively, the plurality of first pump elements that can independently control flow of the hydraulic fluid delivered from the plurality of first delivery ports and the plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from the plurality of second delivery ports. Therefore, it is possible to increase the number of the delivery ports (pump elements) of the pump device. The numbers of the delivery ports (the number of the pump elements) that are connected to the actuators can be increased or reduced depending on required flow rates, so that delivered flow rates can be finely controlled to enhance the operability when the actuators are driven.

[0015] In the pump device including the tandem pump, the first delivery ports and the second delivery ports are open at the side portion of the port block as the shared part of the first hydraulic pump and the second hydraulic pump, and the manifold block having the first and second selector valves mounted therein and having the plurality of service ports formed therein is coupled to the side portion of the port block where the first and second delivery ports are open. Consequently, no hydraulic hoses are required to connect the delivery ports of the port block to the manifold block. Therefore, the pump device is enhanced in its mountability on the construction machine because of a size reduction of the pump device and a reduction in hydraulic hoses.Advantages of the Invention

[0016] According to the present invention, in a pump device and a hydraulic circuit system that use a tandem pump having arranged two hydraulic pumps that can independently control the flow rates of a plurality of delivery ports and use a plurality of selector valves, it is thereby made possible to enhance the operability when the actuators are driven and to enhance the mountability of a pump device on a construction machine by a size reduction and a reduction in hydraulic hoses.Brief Description of the Drawings

[0017] [Fig. 1] Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to a first embodiment of the present invention. [Fig. 2] Fig. 2 is a diagram illustrating a circuit configuration of the hydraulic circuit system according to the first embodiment of the present invention. [Fig. 3] Fig. 3 is a longitudinal cross-sectional view of a pump device along its shaft. [Fig. 4] Fig. 4 is a longitudinal cross-sectional view of the pump device along line A-A of Fig. 3. [Fig. 5] Fig. 5 is a plan view, partly in cross section, of the pump device. [Fig. 6] Fig. 6 is a plan view of the pump device along line B-B of Fig. 3. [Fig. 7] Fig. 7 is a view illustrating part of an electronically controlled hydraulic pump including pump elements, the view being explanatory of operating principles of first and second hydraulic pumps. Modes for Carrying Out the Invention

[0018] An embodiment of the present invention will be described in detail below with reference to the drawings.<First Embodiments

[0019] A first embodiment of the present invention will be described below.~Construction machine-

[0020] Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to the first embodiment of the present invention.

[0021] A hydraulic excavator 100 depicted in Fig. 1 includes a lower track structure 101 having left and right crawler-type track devices 108a and 108b, and an upper swing structure 102 mounted on the lower track structure 101 through a swing device 107 and having a cabin 102a to be occupied by an operator.

[0022] The hydraulic excavator 100 also includes a front work implement 103 having a boom 104 connected to a front portion of the upper swing structure 102. The boom 104 is driven by a boom cylinder 1 as a single-rod hydraulic cylinder 1. An arm 105 is connected to the distal end of the boom 104. The arm 105 is driven by an arm cylinder 2. The arm 105 has a distal end connected to a bucket 106 as a work tool. The bucket 106 is driven by a bucket cylinder 3 as a work tool cylinder. The swing device 107 is driven by a swing motor 4, and the track devices 108a and 108b are driven, respectively, by left and right track motors 5a and 5b.-Hydraulic circuit system-

[0023] Fig. 2 is a diagram illustrating a circuit configuration of the hydraulic circuit system according to the first embodiment of the present invention.

[0024] As illustrated in Fig. 2, the hydraulic circuit system includes an engine 9 as a prime mover, a pump device 10 driven by the engine 9, a plurality of actuators 1 through 5b (see Fig. 5 for the actuators 3 through 5b) driven by hydraulic fluid delivered from the pump device 10, a plurality of directional control valves 21 through 29 for controlling flows of the hydraulic fluid supplied from the pump device 10 to the actuators 1 through 5b, and a plurality of control lever devices 56a, 56b, 56c, and 56d for switching the directional control valves 21 through 29 to operate the actuators 1 through 5b.

[0025] The pump device 10 includes a tandem pump 30 having first and second hydraulic pumps 11 and 12 spaced in an axial direction of a shaft 14 driven and rotated by the engine 9, and a manifold block 40 having four first selector valves 41a through 41d mounted therein as a plurality of first selector valves and four second selector valves 42a through 42d mounted therein as a plurality of second selector valves, and having two first and second service ports 43 and 44 formed therein as a plurality of service ports. The first and second hydraulic pumps 11 and 12 are driven by the engine 9 to introduce the hydraulic fluid from a tank 55 and deliver the hydraulic fluid. The engine 9 may be replaced with an electrically driven motor.

[0026] The first and second hydraulic pumps 11 and 12 have four first delivery ports 45a through 45d as a plurality of first delivery ports and four second delivery ports 46a through 46d as a plurality of second delivery ports, respectively. The first hydraulic pump 11 includes four pump elements 11a through 11d as a plurality of first pump elements that can independently control the hydraulic fluid delivered from the four first delivery ports 45a through 45d. The second hydraulic pump 12 includes four pump elements 12a through 12d as a plurality of second pump elements that can independently control the hydraulic fluid delivered from the four second delivery ports 46a through 46d. Details of the "pump elements" will be described in detail later.

[0027] The manifold block 40 is configured to switch the directions of flows of the hydraulic fluid from the first and second delivery ports 45a through 45d and 46a through 46d with use of the first and second selector valves 41a through 41d and 42a through 42d so as to introduce the hydraulic fluid into either one of the first and second service ports 43 and 44.

[0028] The first and second selector valves 41a through 41d and 42a through 42d are solenoid selector valves that can be switched between a first position that is an initial position and a second position that is a non-initial position. When the first selector valves 41a through 41d are at the first position, they establish communication between the first delivery ports 45a through 45d and the first service port 43. When the first selector valves 41a through 41d are at the second position, they establish communication between the first delivery ports 45a through 45d and the second service port 44. When the second selector valves 42a through 42d are at the first position, they establish communication between the second delivery ports 46a through 46d and the second service port 44. When the second selector valves 42a through 42d are at the second position, they establish communication between the second delivery ports 46a through 46d and the first service port 43.

[0029] The first and second service ports 43 and 44 of the manifold block 40 are connected via respective first and second conduits 51 and 52 to a control valve 20 that houses the directional control valves 21 through 29 in its valve housing.

[0030] The actuators 1 through 5b are the boom cylinder 1, the arm cylinder 2, the bucket cylinder 3, the swing motor 4, the left track motor 5a, and the right track motor 5b, respectively. The directional control valves 21 through 29 are a right track directional control valve 21, a bucket directional control valve 22, a boom I directional control valve 23, a boom directional control valve 27, a swing directional control valve 25, an arm I directional control valve 26, an arm II directional control valve 24, a backup directional control valve 28, and a left track directional control valve 29, respectively.

[0031] The control lever device 56a is used to control the boom 104 and the bucket 106. The control lever device 56b is used to control the arm 105 and the swing device 107. The control lever device 56c is used to control the left track device 108a. The control lever device 56d is used to control the right track device 108b.

[0032] The directional control valves 21 through 29 in the control valve 20 are divided into a first valve group 33 that includes the boom I directional control valve 23 and the boom II directional control valve 27 as directional control valves for a first particular actuator that is operated with relatively high frequency, and a second valve group 34 that includes the arm I directional control valve 26 and the arm II directional control valve 24 as directional control valves for a second particular actuator that is operated with relatively high frequency. The control valve 20 has first and second pump ports 31 and 32 connected respectively to the first and second valve groups 33 and 34. The first and second pump ports 31 and 32 are connected respectively to the first and second service ports 43 and 44 through the respective conduits 51 and 52. The number of the first and second service ports 43 and 44 and the number of the first and second pump ports are two each, identical to the number of the hydraulic pumps 11 and 12 of the tandem pump 30.

[0033] The hydraulic fluid from the first service port 43 flows through the first conduit 51 and the pump port 31 into the control valve 20 where the hydraulic fluid is supplied to the right track directional control valve 21, the bucket directional control valve 22, the boom I directional control valve 23, and the boom II directional control valve 27 of the first valve group 33. The hydraulic fluid from the second service port 44 flows through the second conduit 52 and the pump port 32 into the control valve 20 where the hydraulic fluid is supplied to the swing directional control valve 25, the arm I directional control valve 26, the arm II directional control valve 24, the backup directional control valve 28, and the left track directional control valve 29 of the second valve group 34.

[0034] The first valve group 33 is configured as an open center circuit in which the directional control valves 21, 22, 23, and 27 share a center bypass line 33a and are connected in parallel to each other, whereas the second valve group 34 is configured as an open center circuit in which the directional control valves 24, 25, 26, 28, and 29 share a center bypass line 34a and are connected in parallel to each other.

[0035] When the control lever devices 56a, 56b, 56c, and 56d have their levers not operated and there is no command from a controller 57, the directional control valves 21 through 29 are at a neutral position, with the flows of the hydraulic fluid from the pump port 32 going back to the tank 55 via the center bypass lines 33a and 34a. When the control lever devices 56a, 56b, 56c, and 56d have their levers operated and the controller 57 generates a command, the directional control valves 21 through 29 are switched from the neutral position to adjust the distribution of the flow rates of the flows of the hydraulic fluid from the pump ports 31 and 32 and supply the adjusted flows of the hydraulic fluid to the actuators 1 through 5b. When the boom I directional control valve 23 and the boom II directional control valve 27 are switched from the neutral position, the flows of the hydraulic fluid from these directional control valves 23 and 27 are merged together and supplied to the boom cylinder 1. When the arm I directional control valve 26 and the arm II directional control valve 24 are also switched from the neutral position, the flows of the hydraulic fluid from these directional control valves 24 and 26 are merged together and supplied to the arm cylinder 2.

[0036] The controller 57 is supplied with control signals input from the control lever devices 56a through 56d and sensor signals representing the rotational speed of the engine 9 and various pressures including the delivery pressures of the first and second hydraulic pumps 11 and 12. Then, the controller 57 generates and applies commands to pump controllers 58 and 59, the selector valves 41a through 41d and 42a through 42d, and the control valve 20. In response to commands from the controller 57, the pump controllers 58 and 59 control the delivery flow rates of the first and second pump elements 11a through 11d and 12a through 12d.

[0037] The rotational speed of the engine 9 may be sensed by a rotation sensor such as an encoder disposed with respect to the shaft 14 in the first hydraulic pump 11 or the second hydraulic pumps 12, for example. The delivery pressures of the first and second hydraulic pumps 11 and 12 may be sensed by pressure sensors connected to the conduits 51 and 52, for example. A sensor signal from the rotation sensor is used to control the flow rates of the hydraulic fluid from the first and second pump elements 11a through 11d and 12a through 12d, and sensor signals from the pressure sensors are used to control the horsepower of the hydraulic fluid from the first and second pump elements 11a through 11d and 12a through 12d.-Operation-

[0038] Next, an example of operation for operating the boom 104 and the arm 105 with the configuration described above will be described below.

[0039] As illustrated in Fig. 2, when the levers of the control lever devices 56a, 56b, 56c, and 56d are not operated and there is no command from the controller 57, the first and second selector valves 41a through 41d and 42a through 42d are at the illustrated position, connecting the four pump elements 11a through 11d in the first hydraulic pump 11 to the first valve group 33, and connecting the four pump elements 12a through 12d in the second hydraulic pump 12 to the second valve group 34. In addition, the delivery flow rates of the first and second pump elements 11a through 11d and 12a through 12d are either nil or insignificant. As the directional control valves 21 through 29 are at the neutral position, the hydraulic fluid therefrom flows through the center bypass lines 33a and 34a to the tank 55.

[0040] When the lever of the control lever device 56a is operated in a boom driving direction, the controller 57 issues a command to shift the boom I directional control valve 23 and the boom II directional control valve 27 depending on the lever operation amount (a required flow rate), causing the hydraulic fluid from the first hydraulic pump 11 to drive the boom cylinder 1. As the pump controller 58 issues a command to increase the flow rate of the first hydraulic pump 11, the flow rate of the first hydraulic pump 11 increases depending on the lever operation amount. First, the delivery flow rate of the pump element 11a starts to increase. When the delivery flow rate of the pump element 11a reaches a maximum flow rate, then the delivery flow rate of the pump element 11b increases. When the delivery flow rate of the pump element 11b reaches a maximum flow rate, the delivery flow rate of the pump element 11c increases. When the delivery flow rate of the pump element 11c reaches a maximum flow rate, the delivery flow rate of the pump element 11d increases. If the lever operation amount further increases until only the first hydraulic pump 11 is unable to supply the boom cylinder 1 with the required flow rate, then the second selector valve 42a is switched to add the delivery flow rate of the pump element 12a. If the selector valves 42a, 42b, 42c, and 42d are switched, the entire flow rate of the second hydraulic pump 12 can be added. Specifically, all the eight pump elements 11a through 11d and 12a through 12d can be connected to the boom cylinder 1, making it possible for the boom cylinder 1 to operate at a higher speed.

[0041] When the lever of the control lever device 56b is operated in an arm driving direction, the controller 57 issues a command to shift the arm I directional control valve 26 and the arm II directional control valve 24 depending on the lever operation amount, causing the hydraulic fluid from the second hydraulic pump 12 to drive the arm cylinder 2. As the pump controller 59 issues a command to increase the flow rate of the second hydraulic pump 12, the flow rate of the second hydraulic pump 12 increases depending on the lever operation amount. First, the delivery flow rate of the pump element 12d starts to increase. When the delivery flow rate of the pump element 12d reaches a maximum flow rate, the delivery flow rate of the pump element 12c increases. When the delivery flow rate of the pump element 12c reaches a maximum flow rate, the delivery flow rate of the pump element 12b increases. When the pump element 12b reaches a maximum flow rate, the delivery flow rate of the pump element 12c increases. If the lever operation amount further increases until only the second hydraulic pump 12 is unable to supply the arm cylinder 2 with the required flow rate, then the first selector valve 41d is switched to add the flow rate of the pump element 11d. If the selector valves 41d, 41c, 41b, and 41a are switched, the entire flow rate of the first hydraulic pump 11 can be added. Specifically, all the eight pump elements 11a through 11d and 12a through 12d can be connected to the arm cylinder 2, making it possible for the arm cylinder 2 to operate at a higher speed.

[0042] For simultaneously operating the boom 104 and the arm 105, the lever of the control lever device 56a is operated in the boom driving direction, and the lever of the control lever device 56b is operated in the arm driving direction. Then, the controller 57 issues commands to shift the boom I directional control valve 23 and the boom II directional control valve 27, and also to shift the arm I directional control valve 26 and the arm II directional control valve 24 depending on the lever operation amount (required flow rates). At this time, if the lever of the control lever device 56a is operated by 20% of its maximum operation amount and the lever of the control lever device 56b is operated by 20% of its maximum operation amount, then the pump elements 11a and 11b and the pump elements 12d and 12c deliver the hydraulic fluid, and the boom cylinder 1 is driven by the hydraulic fluid from the pump elements 11a and 11b and the arm cylinder 2 is driven by the hydraulic fluid from the pump elements 12d and 12c. If the control lever devices 56a and 56b input demands in excess of the total maximum flow rate of all the eight pump elements 11a through 11d and 12a through 12d, e.g., if the lever of the control lever device 56a is operated by 100% of its maximum operation amount and the lever of the control lever device 56b is operated by 60% of its maximum operation amount, then the pump elements 11a through 11d and 12a through 12d are distributed depending on the ratio of the operation amounts (100:60 → 5:3), and the boom cylinder 1 is driven by the five pump elements 11a, 11b, 11c, 11d, and 12a, and the arm cylinder 2 is driven by the three pump elements 12d, 12c, and 12b.

[0043] Thus, since the boom cylinder 1 and the arm cylinder 2 are driven independently of each other without the hydraulic fluid from each of the pump elements being divided, the pump elements may supply the hydraulic fluid at the flow rate under the lowest pressure required for the boom cylinder 1 and the arm cylinder 2. Accordingly, the directional control valves are not required to reduce the fluid pressure by constricting the hydraulic fluid, thereby reducing a fluid division loss.~Principles of operation of the first and second hydraulic pumps~

[0044] Each of the first pump elements 11a through 11d and the second pump elements 12a through 12d of the first and second hydraulic pumps 11 and 12 includes a plurality of cylinder working chambers and solenoid valves for changing their net displacements (capacities). On the basis of commands issued from the controller 57 and the pump controllers 58 and 59, the solenoid valves are switched to change the net volumes of the cylinder working chambers, to thereby control the delivery flow rates of the first pump elements 11a through 11d and the second pump elements 12a through 12d. A hydraulic pump that incorporates such pump elements may occasionally be referred to as a digital pump.

[0045] The principles of operation of the first hydraulic pump 11 and the second hydraulic pump 12 will be described in detail below with reference to Fig. 7. Fig. 7 is a schematic view illustrating part of an electronically controlled hydraulic pump 200 including a plurality of pump elements. Each of the first and second hydraulic pumps 11 and 12 has configuration equivalent to the hydraulic pump 200.

[0046] The hydraulic pump 200 has a pump shaft 204 and at least three cylinder working chambers (hereinafter simply referred to as "working chambers") 202 whose volumes are cyclically varied with rotation of the pump shaft 204.

[0047] The hydraulic pump 200 also has low-pressure valves 209 which regulate the flow of hydraulic fluid between a low-pressure manifold 201 communicating with a tank port 216 and the working chambers 202, and high-pressure valves 212 which reguate the flow of the hydraulic fluid between a high-pressure manifold 213 communicating with a delivery port 214 and the working chambers 202.

[0048] The hydraulic pump 200 forms a plurality of pump elements made with the working chambers 202. Each of the pump elements has one or more of the working chambers 202 (typically a plurality of working chambers 202) and is connected to the high-pressure manifold 213 that is common to the plurality of working chambers 202 in the pump elements.

[0049] A controller 207 corresponds to the pump controllers 58 and 59 illustrated in Fig. 2. The controller 207 is configured to actively control at least the low-pressure valves of the working chambers 202 in phased relationship with cycles of working chamber volume to determine whether each working chamber 202 undergoes either an active cycle, with a net displacement of hydraulic fluid between the low-pressure manifold 210 and the high-pressure manifold 213, or an inactive cycle, with no net displacement of hydraulic fluid between the low-pressure manifold 210 and the high-pressure manifold 213, for each cycle of working chamber volume, such that the net displacement of the working chambers 202 of each pump element is controlled in response to a respective demand for hydraulic fluid.

[0050] The hydraulic pump 200 includes a plurality of cylinders 201 which has the working chambers 202 defined by the inner surface of the cylinder 201 and a plurality of pistons 203 driven by an eccentric cam 205 mounted to the pump shaft 204, and which reciprocates within the respective cylinders 201 to cyclically vary the volumes of the working chambers 202 in the cylinders 201. The hydraulic pump 200 further includes a sensor 206 for sensing the angular position and / or the rotational speed of the shaft 204. Information sensed by the sensor 206 is delivered through a signal line 208 to the controller 207, which enables the controller 207 to determine the instantaneous phase of the cycle of each working chamber 202 on the basis of the sensed information.

[0051] Each of the working chambers 202 is associated with the low-pressure valve (LPV) 209 configured as an electronically operated face-sealing poppet valve. The LPV 209 is operable to selectively seal off a channel extending from the working chamber 202 to the low-pressure manifold 210, which may connect one or several working chambers 202, or indeed all of the working chambers 202 in the pump element, to the tank port 216.

[0052] The LPV 209 is a normally open solenoid actuated valve. During an intake stroke in which the pressure within the working chamber 202 is less than or equal to the pressure within the low-pressure manifold 210, the LPV 209 opens passively to bring fluid communication the working chamber 202 with the low-pressure manifold 210, but the LVP 209 is connected to the controller 207 by an LPV control line 211 and selectively closable under active control of the controller 207 to bring the working chamber 202 out of fluid communication with the low-pressure manifold 210. The LPV 209 may alternatively be a normally closed solenoid valve.

[0053] Each of the working chambers 202 is also associated with the high-pressure valve (HPV) 212 in the form of a pressure actuated delivery valve. The HPV 212 opens outwards from the working chamber 202 and is operable to seal off a fluid from the working chamber 202 to the high-pressure manifold 213. When the HPV 212 opens, the high-pressure manifold 213 connects the working chamber 202 to the delivery port 214, allowing the hydraulic fluid to flow from the working chamber 202 to the delivery port 214. The HPV 212 functions as a normally closed pressure-opening check valve that opens passively due to the pressure difference across the HPV 212 against the biasing member in the HPV 212. In some embodiments, the HPV 212 also functions as a normally closed solenoid actuated check valve which the controller 202 may selectively hold opens through HPV control lines 215 once the HPV is opened by pressure within the associated working chamber 202. Typically, the HPV 212 is not operable to open by the controller 207 against the pressure in the high-pressure manifold 213. The HPV 212 may additionally be openable under the control of the controller 207 when there is pressure in the high-pressure manifold 213 but not in the working chamber 202, or may be partially openable.

[0054] In a pumping mode, the controller 207 selects the net rate of displacement of hydraulic fluid from the working chambers 202 to the high-pressure manifold 213 by the hydraulic pump 200 by actively closing one or more of LPVs 209 typically near the point of maximum volume in the volume cycle of the associated working chambers 202, closing the path to the low-pressure manifold 210 and thereby directing the hydraulic fluid tout through the associated HPVs 212 on the subsequent contraction stroke (but does not actively hold open the HPVs 212), causing an active cycle with a net displacement of hydraulic fluid in the working chambers 202. Alternatively, the LPVs 209 may be held open throughout the entire cycles of the working chambers 202 (or the working chambers may be held sealed throughout the entire cycles of the working chambers 202), causing the inactive cycle with no net displacement of hydraulic fluid. The controller 207 selects the numbers and sequence of active and inactive cycles to produce a flow or create a shaft torque or power to satisfy a selected net rate of displacement of hydraulic fluid by the working chambers 202 of the pump elements which are connected to the same high-pressure manifold 213 and the same delivery port 214 to meet a demand for fluid flow from the pump elements.

[0055] As well as determining whether or not to close or hold open the LPVs 209 on a cycle by cycle basis to select between active and inactive cycles, the controller 207 is operable to vary the precise phasing of the closure of the LPVs 209 and / or the HPVs 212 with respect to the varying volumes of the working chambers 202 and thereby to select net rate of displacement of hydraulic fluid from the high-pressure manifold 213 to the low-pressure manifold 210 or vice versa.

[0056] Arrows depicted on the manifolds 210 and 213 indicate flow of the hydraulic fluid in a pump mode, and the flow is reversed in a motor mode.

[0057] In the illustrated example, all of the working chambers 202 are connected to the same high-pressure manifold 213 and the same delivery port 214. Typically, however, the hydraulic pump 200 further includes working chambers 202 forming one or more separate pump elements with their own respective high-pressure manifolds 213, delivery ports 214, and demanded signals.

[0058] More specifically, the first hydraulic pump 11 has four high-pressure manifolds 213 and four delivery ports 214 corresponding to the first delivery ports 45a through 45d, and the high-pressure manifolds 213 are connected to the working chambers 202 via the high-pressure valves 209. The same holds true for the second hydraulic pump 12.

[0059] The demanded signals may use any convenient units. For example, the demanded signal is expressed as "displacement fraction Fd" which is a fraction of maximum possible displacement per revolution of the pump shaft 204. Target flow rate, in volumetric terms, is expressed as the product of the volume change rate Fd and the speed of rotation of the pump shaft 204.~Structure of the pump device~

[0060] The structure of the pump device 10 according to the present embodiment will be described below.

[0061] Figs. 3 through 6 are views illustrating the structure of the pump device 10 in the hydraulic circuit system illustrated in Fig. 1. Fig. 3 is a longitudinal cross-sectional view of the pump device 10 along the shaft 14. Fig. 4 is a longitudinal cross-sectional view of the pump device 10 along line A-A of Fig. 3. Fig. 5 is a plan view, partly in cross section, of the pump device 10. Fig. 6 is a plan view of the pump device 10 along line B-B of Fig. 3.

[0062] The structure of the pump device 10 in the hydraulic circuit system according to the present embodiment will be described below with reference to Figs. 3 through 6.

[0063] In Fig. 3, as described above, the pump device 10 includes the tandem pump 30 having the first and second hydraulic pumps 11 and 12 disposed on the shaft 14 and spaced in the axial direction of the shaft 14, and the manifold block 40 mounting the first selector valves 41a through 41d and the second selector valves 42a through 42d therein (see Fig. 5) and having the two first and second service ports 43 and 44 (see Fig. 5).

[0064] The first and second hydraulic pumps 11 and 12 have a port block 13 configured as a shared part of the first and second hydraulic pumps 11 and 12. As illustrated in Fig. 6, the port block 13 has the four first delivery ports 45a through 45d and the four second delivery ports 46a through 46d that are formed to open at a side portion 13S of the port block 13. The manifold block 40 is coupled to the side portion 13S (see Figs. 3, 5, and 6) of the port block 13 where the first and second delivery ports 45a through 45d and 46a through 46d are open.

[0065] According to the illustrated embodiment, the side portion 13S of the port block 13 has a single block surface, and the first and second delivery ports 45a through 45d and 46a through 46d are open at the block surface. However, the side portion 13S of the port block 13 may have a plurality of stepped surfaces, e.g., a first surface and a second surface parallel to the first surface, and the first delivery ports 45a through 45d may be formed in the first surface whereas the second delivery ports 46a through 46d may be formed in the second surface.

[0066] The first hydraulic pump 11 has a casing 48 and two first radial piston pumps 36a and 36b disposed on a shaft 14a in the casing 48 and spaced in the axial direction of the shaft 14a. The first radial piston pump 36a provides the two first pump elements 11a and 11d among the four pump elements 11a through 11d described above, and the first radial piston pump 36b provides the remaining two first pump elements 11b and 11c.

[0067] Similarly, the second hydraulic pump 12 has a casing 49 and two second radial piston pumps 37a and 37b disposed on a shaft 14b in the casing 49 and spaced in the axial direction of the shaft 14b. The second radial piston pump 37a provides the two second pump elements 12a and 12d among the four pump elements 12a through 12d described above, and the second radial piston pump 37b provides the remaining two second pump elements 12b and 12c.

[0068] The hydraulic fluid from the tank 55 is introduced through an inlet port 47 formed in the port block 13 into a space in the casing 48 where the first radial piston pumps 36a and 36b are housed and a space in the casing 49 where the second radial piston pumps 37a and 37b are housed.

[0069] The first radial piston pump 36a is configured by main components including the shaft 14a that is part of the shaft 14, an eccentric cam 15 that rotates integrally with the shaft 14a, pistons 16 held in sliding contact with the outer circumferential surface of the eccentric cam 15, cylinders 19 in which the pistons 16 reciprocatively move, and an inlet check valve 17a and a delivery check valve 18a that establish communication with cylinder chambers 50 that are formed by the pistons 16 and the cylinders 19. Similarly, the first radial piston pump 36b is also configured by main components including the shaft 14a, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17b, and delivery check valves 18b.

[0070] Likewise, the second radial piston pump 37a is also configured by main components including a shaft 14b, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17c, and delivery check valves 18c, and the second radial piston pump 37b is also configured by main components including the shaft 14b, an eccentric cam 15, pistons 16, cylinders 19, inlet check valves 17d, and delivery check valves 18d.

[0071] The shaft 14a is rotatably supported in the casing 48 and the port block 13 by bearings, and the shaft 14b is rotatably supported in the casing 49 and the port block 13 by bearings. The shafts 14a and 14b are coupled to each other by a coupling 14c, making up the shaft 14.

[0072] As illustrated in Fig. 4, the first radial piston pump 36a has six piston pumps 60 that are configured by the pistons 16 and the cylinders 19 and disposed radially outwardly at equal angular intervals on the shaft 14a. When the eccentric cam 15 that is integral with the shaft 14a rotates, the pistons 16 of the respective piston pumps 60 are reciprocatively moved in the respective cylinders 19, introducing the hydraulic fluid that has filled the space in the casing 48, from the inlet check valves 17a (see Fig. 3) into the cylinder chambers 50, and delivering the hydraulic fluid from the delivery check valves 18a. The delivered hydraulic fluid flows through inner passages 38a and 38d formed in the casing 48 and openings 39a and 39d formed in an end face of the casing 48 that faces the port block 13 into the port block 13, and is introduced therefrom into some of the first delivery ports 45a through 45d illustrated in Fig. 6, i.e., the first delivery ports 45a and 45d according to the embodiment illustrated, from which the hydraulic fluid is delivered.

[0073] Although not illustrated, the first radial piston pump 36b and the second radial piston pumps 37a and 37b are similarly configured. However, with regard to the first radial piston pump 37b, the hydraulic fluid delivered from the delivery check valves 18b is introduced into the first delivery ports 45b and 45c illustrated in Fig. 6, from which the hydraulic fluid is delivered. With regard to the first radial piston pump 37a, the hydraulic fluid delivered from the delivery check valves 18c is introduced into the second delivery ports 46a and 46d illustrated in Fig. 6, from which the hydraulic fluid is delivered. With regard to the second radial piston pump 37b, the hydraulic fluid delivered from the delivery check valves 18d is introduced into the second delivery ports 46b and 46c illustrated in Fig. 6, from which the hydraulic fluid is delivered.

[0074] As illustrated in Fig. 3, the inlet check valve 17a is a solenoid on / off valve (hereinafter referred to as "solenoid valve"). When the solenoid valve is turned off, the solenoid valve is kept open at all times by a spring as depicted at the inlet check valve 17a. The hydraulic fluid that has been introduced into the cylinder 50 upon descent of the piston 16 flows back into the casing 48 through the inlet check valve 17a when the piston 16 ascends, and is not delivered. When the solenoid valve is turned on upon ascent of the piston 16, the solenoid valve is closed as depicted at the inlet check valve 17b, pressurizing the cylinder chamber 50 to open the delivery check valve 18b from which the hydraulic fluid is delivered. By controlling the timing to turn on and off the solenoid valve, the timing to close the inlet check valve is controlled to control the delivery flow rate from the piston 16 during one stroke. Therefore, the flow rates of the piston pumps 60 can be controlled independently of each other by turning on and off the solenoid valves and controlling the timing to turn on and off the solenoid valves.

[0075] According to the present embodiment, the plurality of piston pumps 60 whose flow rates can be controlled independently are used, and a mechanism for merging and delivering the flows of the hydraulic fluid from the plurality of piston pumps 60 is referred to as "pump element."

[0076] According to the present embodiment, moreover, in order to reduce pump pulsations, one pump element uses three piston pumps 60. In the first hydraulic pump 11, the twelve piston pumps 60 of the first radial piston pumps 36a and 36b provide the four pump elements 11a through 11d, and the hydraulic fluid from the pump elements 11a through 11d is delivered from the four delivery ports 45a through 45d. Similarly, in the second hydraulic pump 12, the twelve piston pumps 60 of the second radial piston pumps 37a and 37b provide the four pump elements 12a through 12d, and the hydraulic fluid from the pump elements 12a through 12d is delivered from the four delivery ports 46a through 46d.

[0077] The above features will be further described below with reference to Fig. 4.

[0078] As illustrated in Fig. 4, the six piston pumps 60 of the first radial piston pump 36a are denoted respectively by 60a, 60b, 60c, 60d, 60e, and 60f in clockwise order. The flows of the hydraulic fluid delivered from the piston pumps 60a, 60c, and 60e are merged together to provide the pump element 11a, and the flows of the hydraulic fluid delivered from the piston pumps 60b, 60d, and 60f are merged together to provide the pump element 11d. The merged delivery flow rates flow from the openings 39a and 39d into the port block 13 from which they are introduced into the delivery ports 45a and 45d illustrated in Fig. 6. The first radial piston pump 36b of the first hydraulic pump 11 is of a similar structure. The first radial piston pump 36b provides the two pump elements 11b and 11c, and the merged delivery flow rates from the respective pump elements 11b and 11c are introduced into the delivery ports 45b and 45c illustrated in Fig. 6.

[0079] The second radial piston pumps 37a and 37b of the second hydraulic pump 12 are also of a similar structure. The second radial piston pump 37a provides the two pump elements 12a and 12d, and the merged delivery flow rates from the respective pump elements 12a and 12d are introduced into the delivery ports 46a and 46d illustrated in Fig. 6. The second radial piston pump 37b provides the two pump elements 12b and 12c, and the merged delivery flow rates from the respective pump elements 12b and 12c are introduced into the delivery ports 46b and 46c illustrated in Fig. 6.

[0080] Thus, the six piston pumps 60 of each of the two first radial piston pumps 36a and 36b are divided into two groups, and the flows of the hydraulic fluid delivered from the piston pumps 60 of each group are merged together to provide one of the four pump elements 11a through 11d of the first hydraulic pump 11. Similarly, the six piston pumps 60 of each of the two second radial piston pumps 37a and 37b are divided into two groups, and the flows of the hydraulic fluid delivered from the piston pumps 60 of each group are merged together to provide one of the four pump elements 12a through 12d of the second hydraulic pump 12.

[0081] The manifold block 40 has a block body 40a that is coupled to the side portion 13S of the port block 13 where the eight delivery ports 45a through 45d and 46a through 46d are open. As illustrated in Figs. 3 and 5, the first selector valves 41a through 41d are mounted on a side face of the block body 40a that faces the first hydraulic pump 11, and the second selector valves 42a through 42d are mounted on a side face of the block body 40a that faces the second hydraulic pump 12. The block body 40a has two passages 43a and 44a formed therein on exit sides of the first and second selector valves 41a through 41d and 42a through 42d (on upper sides of the first and second selector valves 41a through 41d and 42a through 42d as illustrated in Fig. 3). The two passages 43a and 44a extend parallel to each other as illustrated in Fig. 5 and are open at respective opposite end faces of the block body 40a. The first service port 43 is formed in the opening of the passage 43a, and the second service port 44 is formed in the opening of the passage 44a. Alternatively, the passages 43a and 44a may be open at an upper surface of the block body 40a to provide the first service port 43 and the second service port 44.

[0082] The block body 40a of the manifold block 40 has inner passages formed therein for introducing the flows of the hydraulic fluid from the eight delivery ports 45a through 45d and 46a through 46d respectively into the solenoid selector valves 41a through 41d and 42a through 42d, and inner passages formed therein for introducing the hydraulic fluid into either one of the passages 43a and 43b depending on whether or not there are commands from the controller 57 to the selector valves 41a through 41d and 42a through 42d. The inner passages provide a hydraulic circuit of the manifold block 40 as illustrated in Fig. 2.~Advantages~

[0083] The present embodiment offers the following advantages: 1. According to the present embodiment, as described above, when the boom 104 alone is to be operated, since the eight pump elements 11a through 11d and 12a through 12d are successively connected to the boom cylinder 1 depending on the lever operation amount (a required flow rate), the number of pump elements (a delivery flow rate) can be finely controlled depending on the lever operation amount, making smooth speed pulsations of the boom cylinder 1, the speed pulsations being due to the switching of the delivery ports by the selector valves 41a through 41d and 42a through 42d, and enhancing operability. Moreover, as it is possible to connect all of the eight pump elements 11a through 11d and 12a through 12d to the boom cylinder 1, the boom cylinder 1 can be operated at a high speed for performing a sufficient amount of work.

[0084] When the arm 105 alone is to be operated, the pump elements are involved in the same manner as when the boom alone is to be operated. The number of pump elements (a delivery flow rate) can be finely controlled depending on the lever operation amount, enhancing operability. Moreover, also it is possible to operate the arm cylinder 2 at a high speed, ensuring a sufficient amount of work.

[0085] If the selector valves 41a through 41d and 42a through 42d are installed at a position spaced from the pump, then eight hydraulic hoses are required to connect the delivery ports 45a through 45d and 46a through 46d to the selector valves 41a through 41d and 42a through 42d. Because the eight hydraulic hoses are connected to the delivery ports 45a through 45d and 46a through 46d, the space through which the hydraulic hoses passes tends to reduce the mountability of the pump device, and there arise many problems including an increase in the man-hours required to connect the hydraulic hoses, a leakage on account of an increased number of hydraulic joints, and a reliability risk. Furthermore, inasmuch as the delivery ports 45a through 45d and 46a through 46d need to be spaced from each other in order to connect the eight hydraulic hoses thereto, the port block 13 is liable to increase in size, making the pump device 10 itself larger in size. This also is likely to lower the mountability of the pump device 10.

[0086] According to the present embodiment, since the manifold block 40 is coupled to the side portion 13S of the port block 13 where the eight delivery ports 45a through 45d and 46a through 46d are open, no hydraulic hoses are required to connect the delivery ports 45a through 45d and 46a through 46d to the selector valves 41a through 41d and 42a through 42d. Therefore, the pump device 10 has enhanced its mountability on the construction machine because of a reduction in the size of the pump device 10 and reduced hydraulic hoses.

[0087] Furthermore, no work for connecting hydraulic hoses occurs, the pump device can be mounted with ease, and leakage locations are reduced, and thus reliability against leakage is enhanced.

[0088] According to the present embodiment, the number of the pump elements and the number of the delivery ports of the first hydraulic pump 11 and the second hydraulic pump 12 are such that the number of the pump elements 11a through 11d, the number of the pump elements 12a through 12d, the number of the delivery ports 45a through 45d, and the number of the delivery ports 46a through 46d are four each. However, these numbers are not limited to such details. The number of the pump elements and the number of the delivery ports of the first hydraulic pump 11 and the second hydraulic pump 12 may be two or more each, e.g., two, three, or five each, to achieve the advantages of the present invention with regard to operability, energy saving, and mountability.

[0089] 2. The control valve 20 is configured such that the first valve group 33 includes the boom I directional control valve 23 and the boom II directional control valve 27, and the second valve group 34 includes the arm I directional control valve 26 and the arm II directional control valve 24. Therefore, when the boom 104 and the arm 105 are to be operated in combination, the boom cylinder 1 and the arm cylinder 2 are driven independently of each other without the need to divide the hydraulic fluid supplied from the pump elements connected thereto. Accordingly, the pump elements may supply the hydraulic fluid at flow rates under minimum pressures required for the boom cylinder 1 and the arm cylinder 2. Thus, the directional control valves are not required to reduce the fluid pressure by constricting the hydraulic fluid, any fluid division loss is reduced, and energy saving is enhanced.

[0090] 3. Since the number of the service ports 43 and 44 of the manifold block 40 and the number of the pump ports 31 and 32 of the control valve 20 that are connected to each other by the conduits 51 and 52 are the same as the number (two) of the first and second hydraulic pumps 11 and 12 of the tandem pump 30, the manifold block 40 and the control valve 20 can be connected by a minimum number of hydraulic hoses. In this regard, too, the number of hydraulic hoses is reduced and the mountability on the construction machine is enhanced.

[0091] 4. The hydraulic circuit in the manifold block 40 is configured such that the first selector valves 41a through 41d establishes communication: at the first position (initial position), between the first delivery ports 45a through 45d and the first service port 43; and at the second position, between the first delivery ports 45a through 45d and the second service port 44, and such that the second selector valves 42a through 42d establishes communication: at the first position (initial position), between the second delivery ports 46a through 46d and the second service port 44; and at the second position, between the second delivery ports 46a through 46d and the first service port 43. Consequently, when the pump elements 11a through 11d are successively connected to the boom cylinder 1 depending on the lever operation amount (a required flow rate) to supply the delivery flow rates from the pump elements 11a through 11d to the boom cylinder 1, since the delivery flow rates can be supplied without the need to switch the selector valves 41a through 41d, no pressure variations occur, the pressure variations being due to the switching of the selector valves 41a through 41d, making it possible to activate or accelerate the boom cylinder 1 smoothly. This holds true also when the pump elements 42a through 42d are successively connected to the arm cylinder 2 depending on the lever operation amount (a required flow rate) to supply the delivery flow rates from the pump elements 12a through 12d to the arm cylinder 2. No pressure variations occur, the pressure variations being due to the switching of the selector valves 42a through 42d, making it possible to activate or accelerate the arm cylinder 2 smoothly.

[0092] When the eight pump elements 11a through 11d and 12a through 12d are successively connected to the boom cylinder 1 to drive the boom cylinder 1 depending on the lever operation amount, any of the selector valves 41a through 41d and 42a through 42d is not switched from the first position until only the first hydraulic pump 11 is able to supply the boom cylinder 11 with the required flow rate, and the selector valves 42a through 42d may be switched to the second position when only the first hydraulic pump 11 is unable to supply the boom cylinder 11 with the required flow rate. This holds true also when the eight pump elements 11a through 11d and 12a through 12d are successively connected to the arm cylinder 2 to drive the arm cylinder 2 depending on the lever operation amount, and the selector valves 41a through 41d may be switched to the second position when only the second hydraulic pump 12 is unable to supply the arm cylinder 2 with the required flow rate. Consequently, the number of times that the selector valves 41a through 41d and 42a through 42d are switched when the boom cylinder 1 or the arm cylinder 2 is to be driven can be reduced, resulting in enhancing the durability of the selector valves 41a through 41d and 42a through 42d.Description of Reference Characters

[0093] 1: boom cylinder (first particular actuator) 2: arm cylinder (second particular actuator) 3: bucket cylinder 4: swing motor 1 to 5b: a plurality of actuators 9: engine 10: pump device 11: first hydraulic pump 11a to 11d: first pump elements 12: second hydraulic pump 12a to 12d: second pump elements 13: port block 14: shaft 15: eccentric cam 16: piston 17a to 17d: inlet check valves 18a to 18d: delivery check valves 19: cylinder 20: control valve 21: right track directional control valve 22: bucket directional control valve 23: boom I directional control valve 24: arm II directional control valve 25: swing directional control valve 26: arm I directional control valve 27: boom 1 directional control valve 28: backup directional control valve 29: left track directional control valve 30: tandem piston 31: first pump port 32: second pump port 33: first valve group 34: second valve group 36a, 36b: first radial piston pumps 37a, 37b: second radial piston pumps 40: manifold block 41a to 41d: first selector valves 42a to 42d: second selector valves 43: first service port 44: second service port 45a to 45d: first delivery ports 46a to 46d: second delivery ports 47: inlet port 48, 49: casings 50: cylinder chamber 51: first conduit 52: second conduit 55: tank 56a, 56b, 56c, 56d: control lever devices 57: controller 58, 59: pump controllers 60a to 60f: piston pumps 100: hydraulic excavator 101: lower track structure 102: upper swing structure 108a, 108b: track device

Examples

first embodiments

[0019]A first embodiment of the present invention will be described below.

~Construction machine-

[0020]Fig. 1 is a diagram illustrating a hydraulic excavator as a typical example of a construction machine that incorporates a hydraulic circuit system according to the first embodiment of the present invention.

[0021]A hydraulic excavator 100 depicted in Fig. 1 includes a lower track structure 101 having left and right crawler-type track devices 108a and 108b, and an upper swing structure 102 mounted on the lower track structure 101 through a swing device 107 and having a cabin 102a to be occupied by an operator.

[0022]The hydraulic excavator 100 also includes a front work implement 103 having a boom 104 connected to a front portion of the upper swing structure 102. The boom 104 is driven by a boom cylinder 1 as a single-rod hydraulic cylinder 1. An arm 105 is connected to the distal end of the boom 104. The arm 105 is driven by an arm cylinder 2. The arm 105 has a dista...

Claims

1. A hydraulic circuit system for a construction machine, the hydraulic circuit system comprising: a prime mover; a pump device driven by the prime mover; a plurality of actuators driven by hydraulic fluid delivered from the pump device; and a plurality of directional control valves that control flows of the hydraulic fluid supplied from the pump device to the plurality of actuators, the pump device comprising a tandem pump including first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by the prime mover, wherein the hydraulic circuit system further comprises a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein, and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open, and the plurality of service ports of the manifold block are connected, through a plurality of conduits, to a control valve having a valve housing that contains the plurality of directional control valves.

2. The hydraulic circuit system for a construction machine according to claim 1, wherein the plurality of service ports of the manifold block are connected, through the plurality of conduits, to a plurality of pump ports formed on the control valve, and number of the plurality of service ports and the plurality of pump ports are same as number of the first and second hydraulic pumps of the tandem pump.

3. The hydraulic circuit system for a construction machine according to claim 1 or claim 2, wherein the plurality of actuators include first and second particular actuators operated with relatively high frequency, the plurality of directional control valves are divided, in the control valve, into a first valve group including two directional control valves for the first particular actuator and a second valve group including two directional control valves for the second particular actuator, the plurality of service ports include first and second service ports, and the plurality of conduits include first and second conduits, and the control valve includes first and second pump ports connected to the first and second valve groups, respectively, and the first and second pump ports are connected to the first and second service ports through the first and second conduits.

4. The hydraulic circuit system for a construction machine according to any preceding claim, wherein the plurality of service ports include first and second service ports, the plurality of first selector valves and the plurality of second selector valves can be switched between a first position that is an initial position and a second position that is a non-initial position, the plurality of first selector valves establish communication between the plurality of first delivery ports and the first service port when the plurality of first selector valves are at the first position, and establish communication between the plurality of first delivery ports and the second service port when the plurality of first selector valves are at the second position, and the plurality of second selector valves establish communication between the plurality of second delivery ports and the second service port when the plurality of second selector valves are at the first position, and establish communication between the plurality of second delivery ports and the first service port when the plurality of second selector valves are at the second position.

5. The hydraulic circuit system for a construction machine according to any preceding claim, wherein the plurality of first pump elements and the plurality of second pump elements of the first and second hydraulic pumps are four first pump elements and four second pump elements, respectively, and the plurality of first delivery ports and the plurality of second delivery ports are four first delivery ports and four second delivery ports, respectively, and the plurality of first selector valves and the plurality of second selector valves of the manifold block are four first selector valves and four second selector valves, respectively.

6. The hydraulic circuit system for a construction machine according to any preceding claim, wherein the first hydraulic pump has a plurality of first radial piston pumps spaced in an axial direction of the shaft, the two first radial piston pumps each have a plurality of piston pumps arranged radially relative to the shaft, the plurality of piston pumps are divided into a plurality of groups, and each group causes the hydraulic fluid delivered from each piston pump within the group to merge together to serve as one of the plurality of pump elements of the first hydraulic pump, the second hydraulic pump has a plurality of second radial piston pumps juxtaposed in the axial direction of the shaft, the two second radial piston pumps each have a plurality of piston pumps arranged radially relative to the shaft, the plurality of piston pumps are divided into a plurality of groups, and each group causes the hydraulic fluid delivered from each piston pump within the group to merge together to serve as one of the plurality of pump elements of the second hydraulic pump.

7. The hydraulic circuit system for a construction machine according to any preceding claim, wherein the plurality of first delivery ports are formed to open at a first surface of the side portion of the port block and the plurality of second delivery ports are formed to open at the first surface or a second surface of the side portion of the port block, parallel to the first surface.

8. A pump device for a construction machine, the pump device comprising: a tandem pump including first and second hydraulic pumps that are spaced in an axial direction of a shaft driven and rotated by a prime mover, wherein the pump device further comprises a manifold block having a plurality of first selector valves and a plurality of second selector valves mounted therein, and having a plurality of service ports formed therein, the first hydraulic pump includes a plurality of first pump elements that can independently control flow of hydraulic fluid delivered from a plurality of first delivery ports, the second hydraulic pump includes a plurality of second pump elements that can independently control flow of the hydraulic fluid delivered from a plurality of second delivery ports, the first and second hydraulic pumps have a port block configured as a shared part of the first and second hydraulic pumps, and having the plurality of first delivery ports and the plurality of second delivery ports formed to open at a side portion of the port block, the manifold block is configured to switch flow directions of the hydraulic fluid having flowed in from the plurality of first delivery ports and the plurality of second delivery ports of the port block, by the plurality of first selector valves and the plurality of second selector valves, and to introduce the hydraulic fluid to any one of the plurality of service ports, and the manifold block is coupled to the side portion of the port block where the plurality of first delivery ports and the plurality of second delivery ports are open.

9. The pump device for a construction machine according to claim 8, wherein the plurality of service ports include first and second service ports, the plurality of first selector valves and the plurality of second selector valves can be switched to a first position that is an initial position and a second position that is a non-initial position, the plurality of first selector valves establish communication between the plurality of first delivery ports and the first service port when the plurality of first selector valves are at the first position, and establish communication between the plurality of first delivery ports and the second service port when the plurality of first selector valves are at the second position, and the plurality of second selector valves establish communication between the plurality of second delivery ports and the second service port when the plurality of second selector valves are at the first position, and establish communication between the plurality of second delivery ports and the first service port when the plurality of second selector valves are at the second position.

10. The pump device for a construction machine according to claim 8 or claim 9, wherein the plurality of first pump elements and the plurality of second pump elements of the first and second hydraulic pumps are four first pump elements and four second pump elements, respectively, and the plurality of first delivery ports and the plurality of second delivery ports are four first delivery ports and four second delivery ports, respectively, and the plurality of first selector valves and the plurality of second selector valves of the manifold block are four first selector valves and four second selector valves, respectively.

11. The pump device for a construction machine according to any of claims 8 to 10, wherein the first hydraulic pump has a plurality of first radial piston pumps spaced in an axial direction of the shaft, the plurality of first radial piston pumps each have a plurality of piston pumps arranged radially relative to the shaft, the plurality of piston pumps are divided into a plurality of groups, and each group causes the hydraulic fluid delivered from each piston pump within the group to merge together to serve as one of the plurality of pump elements of the first hydraulic pump, the second hydraulic pump has a plurality of second radial piston pumps juxtaposed in the axial direction of the shaft, and the plurality of second radial piston pumps each have a plurality of piston pumps arranged radially relative to the shaft, the plurality of piston pumps are divided into plurality of groups, and each group causes the hydraulic fluid delivered from each piston pump within the group to merge together to serve as one of the plurality of pump elements of the second hydraulic pump.

12. The pump device for a construction machine according to any of claims 8 to 11, wherein the plurality of first delivery ports are formed to open at a first surface of the side portion of the port block and the plurality of second delivery ports are formed to open at the first surface or a second surface of the side portion of the port block, parallel to the first surface.

13. The hydraulic circuit system for a construction machine according to any of claims 1 to 7, wherein the first and second hydraulic pumps each comprise: a pump shaft, and at least three working chambers having a volume which varies cyclically with rotation of the shaft, each working chamber of the hydraulic machine comprising: a low-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a low-pressure manifold; and a high-pressure valve which regulates the flow of hydraulic fluid between the working chamber and a high-pressure manifold, wherein the working chambers of the first and second hydraulic pumps form a plurality of pump elements, each pump element comprising one or more of the working chambers and connected to a high-pressure manifold which is common to each working chamber in the pump element, and wherein a controller is provided, and the controller is configured to actively control at least the low pressure valves of the working chambers in phased relationship with cycles of working chamber volume to determine whether each working chamber undergoes either an active cycle, with a net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, or an inactive cycle, with no net displacement of working fluid between the low-pressure manifold and the high-pressure manifold of the working chamber, for each cycle of working chamber volume, such that the net displacement of the working chambers of each pump element is controlled in response to a respective demand for hydraulic fluid.

Images