FLUID PRESSURE CIRCUIT AND WORKING MACHINE

TECHNICAL FIELD

[0001] The present invention relates to a fluid pressure circuit including an accumulator and a working machine with the fluid pressure circuit mounted therein.

BACKGROUND ART

[0002] In working machines, pressure oil discharged from a hydraulic cylinder for a boom during lowering of the boom is accumulated in an accumulator. Furthermore, pressure oil relieved from a slewing hydraulic motor during slewing acceleration or decelerationis also accumulated in the accumulator (see, for example, Patent Document 1) .

[0003]

Patent Document 1: Japanese Patent Application Laid-open No. 2010-84888

[0004] While the pressure oil discharged from the hydraulic cylinder for the boom is being accumulated in the accumulator, the pressure oil discharged from the hydraulic cylinder for the boom is prevented from being recovered in the hydraulic cylinder for the boom. This may preclude a needed pump flow rate from being achieved, reducing the operation speed of the hydraulic, cylinder for the boom. Thus, there has been a desire to achieve the needed pump flow rate by recovering the pressure oil discharged from the hydraulic cylinder for the boom using a simpler configuration.

[0005] With these circumstances in view, it is an object of the present invention to provide a fluid pressure circuit and a working machine that allow a needed pump flow rate to be achieved using a simpler configuration even while a working fluid is being accumulatedunder pressure in an accumulator.

DISCLOSURE OF THE INVENTION

[0006] A first aspect of the present invention is a fluid pressure circuit including a plurality of fluid pressure cylinders that simultaneously performs an identical operation using a working fluid fed under pressure from a pump in accordance with an operation of an operation body, an accumulator in which the working fluid is accumulated under pressure, a pressure accumulation circuit including a first ^" valve that allows an amount by which a head end of a first fluid pressure cylinder and the accumulator communicate with each other to be changed according to an amount of operation of the operation body, the pressure accumulation circuit allowing the working fluid pushed out from the head end of the first fluid pressure cylinder to be accumulated under pressure in the accumulator via the first valve, and a recovery circuit including a second, valve that disables communication betweenhead ends of a plurality of fluid pressure cylinders when pressure accumulation in the accumulator is performed by the pressure accumulation circuit, while enabling communication between a head end of a second fluid pressure cylinder among the plurality of fluid pressure cylinders and both rod ends of the first and second fluid pressure cylinders, the recovery circuit allowing the working fluid pushed out from the head end of the second fluid pressure cylinder to be recovered in the first and second fluid pressure cylinders.

[0007] A second aspect of the present invention is the fluid pressure circuit in the first aspect, in which the first valve allows the amount by which the head end of the first fluid pressure cylinder and the accumulator communicate with each otherto be changed according to the amount of operation of the operation body and an accumulator pressure.

[0008] A third aspect of the present invention is a working machine including a machine body, a working apparatus mounted on the machine body, and the fluid pressure circuit according to the first or second aspect provided for a plurality of fluid pressure cylinders that moves the working apparatus up and down.

[0009] In the first aspect of the present invention, the pressure accumulation circuit is separated from the recovery circuit to allow the working fluid pushed out from the head end of the first fluid pressure cylinder to be accumulated under pressure in the accumulator via the first valve, and at the same time, the working fluid pushed out from the head end of the second fluid pressure cylinder is recovered at the rod ends of the first and second fluid pressure cylinders via the second valve. Thus, even during the pressure accumulation in the accumulator, a pump flow rate corresponding to a recovery flow rate can be saved. The needed pump flow rate can be easily achieved using a simple configuration that uses the first and second valves, and the pump can be miniaturized. Furthermore, the load is concentrated on less than all of the fluid pressure cylinders . This enables an increase in pressure generated by the corresponding fluid pressure cylinder and thus in accumulative pressure energy in the accumulator, allowing the accumulator to be miniaturized.

[0010] In the second aspect of the present invention, the first valve allows the amount by which the head end of the first fluid pressure cylinder and the accumulator communicate with each otherto be changed according to the amount of operation of the operation body and an accumulator pressure. Thus, the pressureaccumulation in the accumulator can be more appropriately achieved.

[0011] In the third aspect of the present invention, even while the accumulator is performing a pressure accumulating operation during lowering of a working apparatus of a working machine, the pump flow rate corresponding to the recovery flow rate can be saved. The needed pump flow rate can be easily achieved, and the pump can be miniaturized. Furthermore, the load is concentrated on less then all of the fluid pressure cylinders. This enables an increase in pressure generated by the corresponding fluid pressure cylinder and thus in the accumulative pressure energy in the accumulator, allowing the accumulator to be miniaturized.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012]

FIG. 1 is a circuit diagram depicting a switching state in an embodiment of a fluid pressure circuit according to the present invention;

FIG. 2 is a circuit diagram of another switching state of the fluid pressure circuit;

FIG. 3A is a diagram schematically illustrating a control algorithm for a first valve in the fluid pressure circuit, and FIG. 3B is a diagram schematically illustrating a control algorithm for a second valve in the fluid pressure circuit; and

FIG. 4 is a perspective view depicting an embodiment of a working machine according to the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

[0013] The present invention will be described below in detail based on an embodiment depicted in FIGS. 1 to 4.

[0014] As depicted in FIG . 4, a hydraulic excavator HE as a working machine has a machine body 1 including a lower traveling body 2 and an upper slewing body 3 provided on the lower traveling body 2 so as to be able to slew using a slewing motor 3m. On the upper slewing body 3, a machine room 4 eguipped with an engine, a pump, and the like is mounted, and a cab 5 that protects an operator and a working apparatus 6 are mounted.

[0015] In the working apparatus 6, a boom 7 that is pivoted in an up-down directionby boom cylinders 7cl and 7c2 serving as two juxtaposed fluid pressure cylinders is pivotally supported at a base end of the boom 7 by the upper slewing body 3. A stick 8 that is pivoted in a front-rear direction by a stick cylinder 8c is pivotally supported at a tip of the boom 7. A bucket 9 that is pivoted by a bucket cylinder 9c is pivotally supported at a tip of the stick 8. The two boom cylinders 7cl and 7c2 are juxtaposed with respect to the common boom 7 and simultaneously perform the same operation.

[0016] FIG. 1 depicts an engine power assist system that accumulates the position energy of the working apparatus 6 in an accumulator via the boom cylinder 7cl while accumulating the kinetic energy of the upper slewing body 3 in the accumulator via a slewing motor 3m such that the accumulated energy is utilized to assist engine power.

[0017] Now, a circuit configuration of the system will be described.

[0018] An assist motor 15 is coupled directly or via a gear or the like to a main pump shaft 14 for main pumps 12 and 13 serving as pumps driven by a engine 11 mounted in the machine room 4. The main pumps 12 and 13 and the assist motor 15 each include a swash plate that enables a pump/motor capacity (piston stroke) to be variably adjusted by varying the angle of the swash plate . The swash plate angle (tilt angle) is controlled by regulators 16, 17, and 18 and detected by swash plate angle sensors 16φ, 17φ, and 18φ. The regulators 16, 17, and 18 are controlled by a solenoid valve. For example, the regulators 16 and 17 for the main pumps 12 and 13 can be automatically controlled by a negative flow control pressure transmitted through a negative flow control passage 19nc and also by a signal other than the negative flow control pressure viasolenoid selector valves 19a and 19b of a negative flow control valve 19.

[0019] The main pumps 12 and 13 discharge, through passages 22 and 23, respectively, hydraulic oil pumped up from a tank 21 and serving as a working fluid. Pump discharge pressures are detected by pressure sensors 24 and 25.A boom energy recovery valve 31 serving as a composite valve connects, via a passage 30, to an output passage 27 extending from a main boom control valve 26 that is included in pilot control valves for directional control and flow control connected to the main pumps 12 and 13 and that controls the boom cylinders 7cl and 7c2and also to an output passage 29 extending from a sub boom control valve 28.

[0020] The boom energy recovery valve 31 is a composite valve incorporating, in a single block, a plurality of circuit functions to switch betweenboth a pressure accumulation circuit A and a recovery circuit B depicted in FIG. 1 and a circuit through which hydraulic oil fed under pressure from the main pumps 12 and 13 is guided toward head ends of the two boom cylinders 7cl and 7c2 during a boom raising operation as depicted in FIG. 2.

[0021] The boom energy recovery valve 31 connects to a passage 32 extending from the head end of the boom cylinder 7cl, via a drift reduction valve 33 through a passage 34, and to a passage 35 extending from the head end of the other boom cylinder 7c2, via a drift reduction valve 36 through a passage 37. Another output passage 38 extending from the main boom control valve 26 is connected to the recovery circuit B for the boom energy recovery valve 31. Rod ends of the boom cylinders 7cl and 7c2 are connected to the boom energy recovery valve 31 through passages 39 and 40, respectively. The drift reduction valves 33 and 36 control opening and closing of ports and the opening degrees of the ports by controlling pilot pressures in spring chambers using respective pilot valves .

[0022] The output passage 27 extending from the main boom control valve 26 can communicate with the output passage 38 via a solenoid selector valve 42 and a check valve 43.

[0023] A discharge side of the assist motor 15 is connected to the tank 21 via a discharge passage 44. A suction side of the assist motor 15 connects to a tank passage 50 extending through a relief valve 48 and a check valve 49 from an accumulator passage 47 provided with a first accumulator 46 including a plurality of accumulators, and to a suction passage 52 through a solenoid selector valve 51. A pressure sensor 55 that detects the pressure of hydraulic oil accumulated in the first accumulator 46 is connected to the accumulator passage 47. The tank passage 50 extends from a tank passage 56 through a check valve 57 with a spring and further through an oil cooler 58 or a check valve 59 with a spring and connects to the tank 21. The first accumulator 46, the accumulator passage 47, the relief valve 48, the solenoid selector valve 51, and the pressure sensor 55 are assembled in a single block to form an accumulator block 60.

[0024] The boom energy recovery valve 31 includes a control valve 61 serving as a first valve forming a part of the pressure accumulation circuit A and a main control valve 62 that is a boom circuit selector valve serving as a second valve forming a part of the recovery circuit B. The control valve 61 and the main control valve 62 may be of a pilot operated type that is switched by controlling application and release of the pilot pressure using a solenoid selector valve operated by operating a lever that is an operation body operated by, for example, an operator in the cab 5 (FIG. 4) and not depicted in the drawings. However, in the drawings , the control valve 61 and the main control valve 62 are depicted as solenoid proportional directional control valves for

clarification of description.

[0025] The control valve 61 is a flow control valve that permits the boom cylinder 7cl to accumulate pressure in the first accumulator 46 (accumulator block 60) by enabling and disabling, in a switchable manner, communication between the passage 34 and a passage 68 connecting to the first accumulator 46 through a check valve 67. The control valve 61 is a valve that allows more hydraulic oil to flow from the boom cylinder 7cl to the first accumulator 46 than from the normal cylinder (boom cylinder 7cl or 7c2 or the like) back to the tank 21. That is, the control valve 61 gives priority to accumulation of pressure oil in the first accumulator 46.

[0026] The main control valve 62 separates the boom cylinder 7cl and the boom cylinder 7c2 into a pressure accumulation cylinder and a self-recovery cylinder by switching the relation between the passage 71 and the passage 72, the relation between the passage 73 and the passage 74, and the relation between the passage 75 and the passage 76. That is, the main control valve 62 is configured so as to disable the communication between the head ends of the boom cylinders 7cl and 7c2 while enabling the communication between the head end of the boom cylinder 7c2 and the rod end of each of the boom cylinders 7cl and 7c2 when the control valve 61 performs switching to accumulate pressure in the first accumulator 46.

[0027] The passage 71 connects to the passage 30 through a check valve 78. The passage 72 connects to a passage 79 branching from the passage 37 and the passage 30. The passage 73 branches from the passage 72. The passage 74 connects to the passage 40 through a check valve 80. The passage 75 connects to the output passage 38 and the passage 39. The passage 76 branches from the passage 40.

[0028] As depicted in FIG. 1, the pressure accumulation circuit A is a circuit extending through the passage 32 from the head end of the boom cylinder 7cl, through the drift reduction valve 33 and the passage 34, through the control valve 61 and check valve 67 in the boom energy recovery valve 31, and through the passage 68 to the first accumulator 46. The pressure accumulation circuit A has a function to accumulate oil pushed out from the head end of the boom cylinder 7clunder pressurein the first accumulator 46.

[0029] The recovery circuit B is a circuit extending through the passage 35 from the head end of the other boom cylinder 7c2, through the drift reduction valve 36 and the passage 37, through the passage 73, the main control valve 62, the passage 74, the check valve 80, and the passage 40 in the boom energy recovery valve 31 to the rod endof the other boom cylinder 7c2 and also extending through the passage 35, through the drift reduction valve 36 and the passage 37, through the passage 73, the main control valve 62, the passage 74, the check valve 80, the passage 76, the main control valve 62, the passage 75, and the passage 39 in the boom energy recovery valve 31 to the rod end of the other boom cylinder 7cl. The recovery circuit B has a function to recover oil pushed out from the head end of the boom cylinder 7c2 at the rod end of each of the boom cylinders 7cl and 7c2.

[0030] Opposite relief valves 94 and 95 and opposite check valves 97 and 98 are provided between passages 92 and 93 for a motor driving circuit C that connects a slewing motor 3m and a slewing control valve 91 that controls a slewing direction and a speed of the slewing motor 3m. A makeup passage 99 is connected betweenthe relief valves 94 and 95 and between the check valves 97 and 98; the makeup passage 99 has a tank passage function to return oil discharged from the motor driving circuit C to the tank 21 and a makeup function to enable the motor driving circuit C to be refilled. The makeup passage 99 connects to a second accumulator 100 that supplies pressure oil. Under a pressure that is lower than a spring bias pressure of the check valve 57 with the spring, hydraulic oil is fed through the makeup passage 99 and through the check valves 97 and 98 to sides of the passages 92 and 93 on which vacuum may occur.

[0031] The passages 92 and 93 in the motor driving circuit C are brought into communication with a slewing energy recovery passage 104 through check valves 102 and 103. The passage 104 is connected to a passage 106 through a sequence valve 105 in which an original pressure at an inlet is unlikely to be changed by a backpressure at an outlet. The passage 106 is connected to the first accumulator 46 and the passage 68.

[0032] In the circuit configuration as described above , the swash plate angle sensors 16φ, 17φ, and 18φ and the pressure sensors 24, 25, and 55 input detected swash plate angle signals and pressure signals to an in-vehicle controller (not depicted in the drawings) . The valves 42 and 51 are switched through a turn-on and -off operation in accordance with a driving signal output from the in-vehicle controller (not depicted in the drawings) or through a proportional operation in accordance with the driving signal. The boom control valves 26 and 28, the slewing control valve 91, and other hydraulic actuator control valves not depicted in the drawings ( for traveling motors , a stick cylinder , a bucket cylinder, and the like) are pilot-operated using a manually operated valve operated by the operator in the cab 5 (FIG. 4) or the like using a lever or a pedal, what is called a remote control valve. Pilot valves in the drift reduction valve 33 and 36 are also pilot-operated in conjunction with the operation of the above-described control .valves.

[0033] Control performed by the in-vehicle controller will be described below in terms of functions.

[0034] FIG. 1 depicts a circuit state during a boom lowering operation of lowering the boom 7. Hydraulic oil pushed out from the head end of the boom cylinder 7cl due to the load on the working apparatus 6 or the like flows through the passage 32, the drift reduction valve 33, and the passage 34 and then through the check valve 67 under the effect of the control valve 61 in the boom energy recovery valve 31 that has been switched to a communication position The hydraulic oil is thus brought into communication with the passage 68, passes through the passage 68, and then isaccumulated in the first accumulator 46 under pressure. At this time, the control valve 61 allows switching of the amount by which the head end of the boom cylinder 7cl and the first accumulator 46 communicate with each other according to the amount of operation of the lever, that is, the pilot pressure set based on the amount of operation, and the accumulator pressure in the first accumulator 46 detected by the pressure sensor 55. Specifically, the pilot pressure set based on the lever operation amount is corrected in accordance with a predetermined table, and the accumulator pressure is corrected in accordance with a predetermined table. Then, integration results obtained are output to operate the control valve 61. More specifically, in the present embodiment, the following operation is performed as illustrated in FIG. 3A. When the pilot pressure set based on the lever operation amount is relatively low, the amount of increase in output pressure is large relative to the amount of increase in input pressure. In a region where the pilot pressure set based on the lever operation amount exceeds a threshold THl, the amount of increase in output pressure relative to the amount of increase in input pressure is kept small compared to a region where the amount of increase in output pressure is equal to or smaller than the threshold THl . In a region where the pilot pressure exceeds a predetermined threshold TH2 that is larger than the predetermined threshold THl, the output pressure is set constant. In a region where the accumulator pressure is equal to or lower than a predetermined threshold TH3, gain increases relative to the amount of increase in accumulator pressure. In a region where the accumulator pressure exceeds the predetermined threshold TH3, the gain is set to a constant value (for example, 1) . At this time, the check valve 78 prevents the hydraulic oil from returning toward the boom control valve 26.

[0035] At the same time, the hydraulic oil pushed out from the head end of the other boom cylinder 7c2 flows through the passage 35, the drift reduction valve 36, and the passage 37 and then has the direction thereof controllably changed from the passage 73 to the passage 74 by the main control valve 62 in the boom energy recovery valve 31. The hydraulic oil further flows through the check valve 80 and the passage 40 and is recovered at the rod end of the other boom cylinder 7c2. Furthermore, the hydraulic oil branching to the passage 76 through the check valve 80 has the direction thereof controllably changed to the passage 75 through the check valve in the main control valve 62, and is recovered at the rod end of the boom cylinder 7cl through the passage 39. At this time, the amount of operation of the main control valve 62 changes according to the lever operation amount, that is, the pilot pressure set based on the lever operation amount. Specifically, the pilot pressure set based on the lever operation amount is corrected in accordance with the predetermined table to provide an output that allows the main control valve 62 to be operated. More specifically, in the present embodiment, as illustrated in FIG. 3B, an input pressure and an output pressure are set for the pilot pressure set based on the lever operation amount in accordance with a table similar to the table illustrated in FIG. 3A, and are basically immediately switched when a boom raising operation is detected. A surplus flow rate of the hydraulic oil pushed out from the head end of the other boom cylinder 7c2 flows through the passage 37, the passage 79, and the passage 30 to return to the tank 21 via the boom control valve 26. Additionally, when raising of the machine body 1 by lowering of the boom is detected by, for example, detecting grounding of the working apparatus 6 (FIG. 4) based on the head end pressures of the boom cylinders 7cl and 7c2, the separation of the boom cylinders 7cl and 7c2 into the pressure accumulation cylinder and the self-recovery cylinder is canceled in accordance with a predetermined set value.

[0036] As described above, the boom energy recovery valve 31 allows the pressure accumulation in the first accumulator 46 during boom lowering and the recovery at the rod ends of the boom cylinders 7cl and 7c2 to be simultaneously achieved via the control valve 61 and the main control valve 62.

[0037] FIG. 2 illustrates a circuit state during a boom raising operation of raising the boom 7. During the boom raising operation, the boom energy recovery valve 31 switches the control valve 61 to a shutoff position while switching the main control valve 62 to stop the pressure accumulation in the first accumulator 46 and the recovery at the rod ends of the boom cylinders 7cl and 7c2. The hydraulic oil fed from the main pumps 12 and 13 to the passage 30 through the boom control valves 26 and 28 is guided through the passage 79, the passage 37, the drift reduction valve 36, and the passage 35 to the head end of the other boom cylinder 7c2 and also through the check valve 78, the passage 34, the drift reduction valve 33, and the passage 32 to the head end of the boom cylinder 7cl. The hydraulic oil pushed out from the rod end of the boom cylinder 7cl flows through the passage 39, the output passage 38, and the boom control valve 26 back to the tank 21. The hydraulic oil pushed out from the rod end of the boom cylinder 7c2 flows through the passage 40 and the passage 76, has the direction thereof controllably changed to the passage 75 by the main control valve 62, and then passes through the output passage 38 and the boom control valve 26 back to the tank 21.

[0038] During the boom lowering operation, the boom raising operation, and the like, engine power assist may be performed in which the assist motor 15 coupled directly or via a gear to the main pump shaft 14 and having a motor function is allowed to function as a hydraulic motor to reduce the engine load as depicted in FIG. 2. For example, during the boom lowering operation, the engine power assist is performed when theaccumulator pressure in the first accumulator 46 detected by the pressure sensor 55 is equal to or higher than a first threshold pressure. During an operation other than the boom lowering operation, for example, during the boom raising operation, the engine power assist is performed when the accumulator pressure in the first accumulator 46 detected by the pressure sensor 55 is equal to or higher thana predetermined second threshold pressure that is different from the first threshold pressure. During the engine power assist, the solenoid selector valve 51 is switched to the communication position to allow the assist motor 15 to rotate using the energy accumulated in the first accumulator 46. Thus, hydraulic outputs from the main pumps 12 and 13 are assisted to reduce the engine load. The engine power assist based on the assist motor 15 is not performed while the machine body 1 is being raised.

[0039] As described above, the engine power assist function rotates the assist motor 15 using the energy accumulated in the first accumulator 46 through the head end of the boom cylinder 7cl, whereby the load on the mounted engine 11 coupled to the assist motor 15 via the main pump shaft 14 is reduced by the assist motor 15.

[0040] As described above, when the pressure accumulation circuit Ά and the recovery circuit B are disconnected from each other to lower the working apparatus 6 of the hydraulic excavator HE, the hydraulic oil pushed out from the head end of the boom cylinder 7cl is accumulated under pressure in the first accumulator 46 via the control valve 61, while the hydraulic oil pushed out from the head end of the boom cylinder 7c2 is recovered at the rod ends of the boom cylinders 7cl and 7c2 via the main control valve 62. Thus, even while the first accumulator 46 is performing a pressure accumulation operation, a pump flow rate corresponding to a recovery flow rate can be saved. This allows the needed pump flow rate including the main pump flow rate needed for the hydraulic actuator to be easily achieved using the simple configuration with the control valves 61 and 62, and also enables the main pumps 12 and 13 to be miniaturized.

[0041] The oil from the head end of the boom cylinder 7cl is used for the pressure accumulation in the first accumulator 46, that is, the load on the working apparatus 6 is concentrated on the single boom cylinder 7cl instead of being distributed between the two boom cylinders 7cl and 7c2. Thus, energy density can be increased to elevate the pressure generated by the boom cylinder 7cl, enabling an increase in the accumulative pressure energy in the first accumulator 46. In other words, components such as the first accumulator 46 and the assist motor 15 can be miniaturized, keeping costs low and facilitating layout.

[0042] The control valve 61 allows the amount by which the head end of the boom cylinder 7cl and the first accumulator 46 communicate with each other to be changed according to the lever operation amount and the accumulator- pressure in the first accumulator 46. Thus, the pressure accumulation in the first accumulator 46 can be more appropriately achieved without sacrifice of the operability of boom lowering, allowing both appropriateoperation and energy

accumulation to be simultaneously accomplished. [0043] While the boom cylinders 7cl and 7c2 are performing an operation interlocked with operations of the other hydraulic actuators (the slewing motor 3m, the stick cylinder 8c, the bucket cylinder 9c, and the like) , the hydraulic oil pushed out from the head end of the boom cylinder 7c2 is recovered at the rod ends of the boom cylinders 7cl and 7c2. Thus, thisamount of recovered oil can be routed to the other hydraulic actuators through the main pumps 12 and 13. This allows prevention of a decrease in speed during the interlocked operation and improvement of interlocking operability .

[0044] The boom energy recovery valve 31 with the plurality of circuit functions integrated in the single block facilitates the layout to reduce assembly man-hour, enabling a reduction in costs.

[0045] The load is concentrated on the boom cylinder 7cl to enable an increase in the accumulative pressure energy in the first accumulator 46 to allow a small-sized accumulator to perform significant assistance. Thus, the costs can be kept low and the machine body layout can be made compact.

INDUSTRIAL APPLICABILITY

[0046] The present invention has industrial applicability for operators engaged in manufacture, sale, and the like of fluid pressure circuits or working machines.

EXPLANATION .OF REFERENCE NUMERALS

[0047] A Pressure accumulation circuit

B Recovery circuit

HE Hydraulic excavator HE as working machine

1 Machine body

6 Working apparatus

7cl, 7c2 Boom cylinders serving as fluid pressure cylinders

12, 13 Main pumps serving as pumps

46 First accumulator that is an accumulator

61 Control valve serving as first valve

62 Main control valve serving as second valve