JP2009275772A - Fluid pressure control circuit - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluid pressure control circuit which facilitates the accumulation of a working fluid into an accumulator, and provides a high pressure when the fluid is reused. <P>SOLUTION: The head side of a potential energy recovery cylinder Cy1 is communicated with the accumulator Acc through one recovery control valve 1. The suction port of a dedicated pump Pp2 driven together with a main pump Pp1 by an engine E is connected to the accumulator Acc. The discharge port of the dedicated pump Pp2 is communicated with a recovery passage between the head and the rod of the potential energy recovery cylinder Cy1 through the one reuse control valve 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a fluid pressure control circuit including an accumulator for recovering potential energy.

In a hydraulic excavator that moves a work machine up and down by a boom cylinder, the head side of the boom cylinder is connected to an accumulator via an accumulator operation valve, and connected to a tank via a variable relief valve. According to the position of the machine, there is a position energy recovery and utilization device for a hydraulic excavator that controls the accumulator operation valve and the variable relief valve to generate hydraulic pressure in the accumulator that balances the weight of the work machine (for example, Patent Document 1).
Japanese Patent Laid-Open No. 01-199001 (page 2-3, FIG. 1)

  This conventional one stores a part of the return oil flowing out from the head side of the boom cylinder in the accumulator through the accumulator operation valve, but it is not easy to set the set pressure of this accumulator properly, If the pressure is too low, the pressure at the time of reuse is not sufficient, and if the set pressure is too high, the pressure in the accumulator becomes the load pressure, and the lowering speed and responsiveness of the boom cylinder are reduced.

  The present invention has been made in view of these points, and an object of the present invention is to provide a fluid pressure control circuit that can easily accumulate a working fluid in an accumulator and can obtain a high pressure during reuse.

  The invention described in claim 1 includes a main circuit that controls the working fluid discharged from the main pump and supplies the working fluid to the potential energy recovery cylinder, an accumulator that accumulates the working fluid discharged from the potential energy recovery cylinder, and an accumulator It is a fluid pressure control circuit provided with the exclusive pump which sucks the working fluid discharged from and supplies it to the potential energy recovery cylinder.

  According to a second aspect of the present invention, there is provided the fluid pressure control circuit according to the first aspect, wherein the fluid pressure control circuit includes a recovery control valve that controls a flow when the working fluid discharged from the potential energy recovery cylinder is recovered by the accumulator. It is a control circuit.

  According to a third aspect of the present invention, in the fluid pressure control circuit according to the first or second aspect, a reuse control valve for controlling a flow when the working fluid discharged from the dedicated pump is reused in the potential energy recovery cylinder. Is a fluid pressure control circuit.

  According to a fourth aspect of the present invention, there is provided a fluid pressure control in which the potential energy recovery cylinder in the fluid pressure control circuit according to any one of the first to third aspects is a boom cylinder that rotates a working device of a hydraulic excavator in the vertical direction. Circuit.

  According to the first aspect of the present invention, when the working fluid accumulated in the accumulator is reused in the potential energy recovery cylinder, pressurization with a dedicated pump is possible, so it is necessary to set the accumulator pressure high. Therefore, the accumulator pressure can be set to a low pressure, the working fluid can be easily accumulated in the accumulator, and a high pressure can be obtained during reuse.

  According to the second aspect of the present invention, since the accumulator pressure can be set to a low pressure by the dedicated pump, the potential energy recovery cylinder using the accumulator pressure as the load pressure can be quickly operated by opening the recovery control valve, and the potential energy The operating speed and responsiveness of the recovery cylinder can be improved.

  According to the third aspect of the present invention, the working fluid accumulated in the accumulator can be reused for the potential energy recovery cylinder via the dedicated pump by opening the reuse control valve. The operating speed and responsiveness can be further improved.

  According to the fourth aspect of the present invention, when the working device of the hydraulic excavator is moved up and down by the boom cylinder, the working fluid can be easily accumulated in the accumulator and a high pressure can be obtained at the time of reuse.

  Hereinafter, the present invention will be described in detail with reference to an embodiment shown in FIGS.

  As shown in FIG. 3, a hydraulic excavator 10 as a work machine is provided with a work device 12 as a load body movably provided to a machine body 11, and the work device 12 is connected to the machine body 11 and the machine body 11. A base end portion and a rod end portion of a boom cylinder 14 as a potential energy recovery cylinder are rotatably connected to a boom 13 that is pivotally supported so as to be rotatable in the vertical direction. The base end of the arm cylinder 16 and the tip of the rod are pivotally connected to the arm 15 pivotally supported at the distal end, and further pivoted to the arm 15 and the distal end of the arm 15. A linkage 17 at the base end portion of the bucket cylinder 18 and a tip end portion of the rod is rotatably connected to the bucket 17 that is pivotally supported.

  The boom cylinder 14 is a fluid pressure actuator that rotates the working device 12 in the vertical direction. The boom cylinder 14 is a potential energy recovery cylinder that can perform a reduction operation in response to the entire load W of the working device 12. It is called cylinder Cy1. Further, other fluid pressure actuators (hydraulic cylinder or hydraulic motor) other than the potential energy recovery cylinder Cy1 are referred to as other circuit cylinder Cy2.

  FIG. 1 shows a specific system configuration example. The head side of the potential energy recovery cylinder Cy1 is provided so as to be able to communicate with an accumulator Acc via one recovery control valve 1, and is also a variable capacity driven by an engine E. The discharge passage of the main pump Pp1 is provided so as to be able to communicate with the accumulator Acc via the other recovery control valve 2. A part of the fluid discharged from the head side of the potential energy recovery cylinder Cy1 or the fluid discharged from the main pump Pp1 is accumulated in the accumulator Acc.

  The accumulator Acc is connected to a suction port of a variable capacity type dedicated pump Pp2 driven by the engine E together with the main pump Pp1. The discharge port of the dedicated pump Pp2 is connected to one of the recycle control valves 3 to recover potential energy. The cylinder Cy1 is provided so as to be able to communicate with the head-rod regeneration passage, and is provided so as to be able to communicate with the discharge passage of the main pump Pp1 via the other reuse control valve 4.

  In addition, a regeneration control valve 5 is provided in a regeneration passage that allows the head side of the potential energy recovery cylinder Cy1 to communicate with the rod side. Between the regeneration passage and the main pump Pp1, a closing control valve 6 and a pump flow rate are provided. A control valve 7 is provided. The discharge passage of the main pump Pp1 is connected to the supply port of the pump flow rate control valve 7.

  The recovery control valve 1 is for positional energy recovery control for controlling the flow rate when recovering the working fluid discharged from the head side of the potential energy recovery cylinder Cy1 to the accumulator Acc.

  The recovery control valve 2 controls the flow of recovering the excess flow rate from the main pump Pp1 to the accumulator Acc.

  The reuse control valve 3 controls the regeneration flow rate when the working fluid on the head side of the potential energy recovery cylinder Cy1 discharged from the dedicated pump Pp2 is reused on the rod side of the potential energy recovery cylinder Cy1.

  The reuse control valve 4 controls the flow of reusing the accumulated energy of the accumulator Acc via the dedicated pump Pp2, and is connected to the discharge line of the main pump Pp1.

  The regeneration control valve 5 controls when the fluid is directly regenerated from the head side to the rod side of the potential energy recovery cylinder Cy1, but is not essential and may be deleted together with the regeneration passage.

  The closing control valve 6 is necessary and essential when the pump flow rate control valve 7 cannot close the flow path to the tank T side during regeneration from the head side to the rod side of the potential energy recovery cylinder Cy1. is not.

  The pump flow rate control valve 7 controls the direction of the pump injection flow rate injected into each load body drive device (boom cylinder 14, arm cylinder 16, bucket cylinder 18, etc.) and the return flow rate returned from each load body drive device to the tank T. The control valve for controlling the flow rate may be a spool valve in which the relationship between the injection flow rate and the return flow rate is fixed, but the relationship between the injection flow rate and the return flow rate can be controlled separately by a plurality of logic valves. desirable.

  One output port of the pump flow control valve 7 is connected to the head side of the potential energy recovery cylinder Cy1 via the passage M, and the other port is connected to the rod side of the potential energy recovery cylinder Cy1 via the closing control valve 6. Has been. The connection control object of this pump flow rate control valve 7 includes not only the position energy recovery cylinder Cy1 such as a boom cylinder for recovering potential energy but also other circuit cylinders Cy2 such as a bucket cylinder, and each of the plural circuits has flow control and direction control. To do.

  In FIG. 1, the reuse control valve 4 is connected to the upstream side of the pump flow control valve 7, but when limiting the subsystem (circuit such as a boom cylinder) to be reused, It may be connected downstream. At this time, when the flow of the recovery control valve 1 is set in both directions and the recovery control valve 1 is also used for injection to the head side, the reuse control valve 4 is not necessary.

  The dedicated pump Pp2 sucks the working fluid released from the accumulator Acc when flowing high-pressure fluid when reusing the accumulated energy of the accumulator Acc (in the reuse mode), and the head side of the potential energy recovery cylinder Cy1 or the main Further, the fluid is supplied to the discharge passage of the pump Pp1, and the fluid on the head side of the potential energy recovery cylinder Cy1 is supplied as a regeneration flow rate to the rod side of the potential energy recovery cylinder Cy1 via the reuse control valve 3 in the potential energy recovery mode. It has a function and has a flow rate adjustment function by means of variable capacity such as a swash plate.

  In FIG. 1, only one set of cylinders (boom cylinders, etc.) constituting the fluid pump and each circuit is illustrated, but a plurality of sets may be installed.

  An operation lever (electric joystick) that inputs the operation direction and operation command speed of the potential energy recovery cylinder Cy1, etc. as an operation command L, and pressure sensors Sph, Spr that detect the head pressure Ph and rod pressure Pr of the potential energy recovery cylinder Cy1, respectively. The pressure sensor Sac that detects the accumulator pressure Pa stored in the accumulator Acc, the angle sensor San that detects the angle θ of the load body such as the boom 13, the pressure sensor Spp that detects the discharge pressure Ppo of the main pump Pp1, and the dedicated pump Pp2 Pressure sensor Spp2 for detecting the discharge pressure Ppp2, pressure sensor Snfc for detecting the negative flow control pressure Pnfc generated in the center bypass line of the pump flow control valve 7, and the gas temperature charged in the accumulator Acc (hereinafter referred to as accumulator temperature Ta) A temperature sensor Sta for detecting is connected to the input unit of the control device 8.

  This control device 8 incorporates an arithmetic processing device, a storage device, etc., and the output unit of this control device 8 is a movable control unit (such as a solenoid) of each control valve 1-7 and variable capacity control of the main pump Pp1. Connected to the control unit (swash plate regulator, etc.) and the capacity variable control unit (swash plate regulator, etc.) of the dedicated pump Pp2, and these are controlled by electric signals. A one-dot chain line in FIG. 1 represents a control signal line, and a solid line represents a hydraulic line.

  The control device 8 grasps the accumulation state (accumulator filling rate) of the accumulator Acc by calculating the accumulator pressure Pa detected by the pressure sensor Sac and the enclosed gas temperature Ta of the accumulator Acc detected by the temperature sensor Sta. Therefore, the control valves 1 to 7, the main pump Pp1 and the dedicated pump Pp2 are controlled based on the accumulation state and the flow rate request state based on the operation command L input from the operation lever.

  A fluid pressure circuit that controls the working fluid discharged from the main pump Pp1 according to the operation command L and supplies the working fluid to the potential energy recovery cylinder Cy1 or the other circuit cylinder Cy2 is referred to as a main circuit 9 for the accumulator circuit. Although only one operation command L is shown, it is input to the control device 8 for each cylinder, and the displacement amount of the spool (or stem) in the pump flow rate control valve 7 and the target value in the displacement direction for each cylinder. Become.

  In such a potential energy recovery / reuse system, if the frictional force is ignored, the force balance equation is as follows.

  The pressure on the head side from the piston of the potential energy recovery cylinder Cy1 detected by the pressure sensor Sph is the head pressure Ph, the area on the head side of the piston is the header area Ah, and from the piston of the cylinder Cy detected by the pressure sensor Spr The rod side pressure is the rod pressure Pr, the rod side area of the piston is the rod area Ar, the load body mass is m, the second order differential of the cylinder position X, that is, the acceleration is α, and the friction force is ignored. The equilibrium equation is as follows.

  m ・ α ＝ W + （Pr ・ Ar−Ph ・ Ah） …… (1)

  In an equilibrium state where the cylinder speed is constant, both sides of equation (1) are zero.

  The accumulator pressure stored in the accumulator Acc is Pa, and the initial pressure of the accumulator Acc (slightly higher than the enclosed gas pressure) is PaO.

  An arrow N shown in FIG. 1 is a flow path from the existing system to the rod side of the potential energy recovery cylinder Cy1, and is used in a mode other than the potential energy recovery mode.

  In the potential energy recovery mode, the flow rate discharged from the main pump Pp1 is set to 0 in principle, and the working fluid discharged from the potential energy recovery cylinder Cy1 is lowered while the potential energy recovery cylinder Cy1 is lowered by the load W of the working device 12. This is a control mode that accumulates in the accumulator Acc. The recovery control valve 2, the reuse control valve 4 and the pump flow rate control valve 7 are closed, the recovery control valve 1, the reuse control valve 3 and the regeneration control valve 5 are opened, and the dedicated pump Pp2 To control the flow rate.

  If necessary, the control device 8 allows a part of the head side fluid of the potential energy recovery cylinder Cy1 to flow to the rod side of the potential energy recovery cylinder Cy1 via the dedicated pump Pp2 and the reuse control valve 3. The pressure Pr can be increased, the right side of the equation (1) can be increased, and the downward acceleration α can be increased.

At this time, the accumulated flow rate Q1 to the accumulator Acc and the flow rate Q2 to the rod side are:
Q1 = Cd · A · √ (Ph-Pa), where Cd is a constant Q2 = volume of the dedicated pump Pp2 × number of revolutions, A can be freely controlled by the opening of the recovery control valve 1, the volume of the dedicated pump Pp2 Can be freely controlled by the swash plate, the ratio of these flow rates Q1 and Q2 can also be set freely.

  As an example of the potential energy recovery mode, the control device 8 first opens the regeneration control valve 5 so that the fluid flowing out from the head side of the potential energy recovery cylinder Cy1 is regenerated to the rod side. The potential energy recovery cylinder Cy1 that receives the load W generates acceleration in the downward direction, the head speed Ph and the rod pressure Pr increase as the cylinder speed increases, and the head pressure Ph becomes the accumulator initial pressure. When PaO is exceeded, the regeneration control valve 5 is throttled and the collection control valve 1 is opened to supply and accumulate the flow rate from the head side to the accumulator Acc.

  Next, the features of this embodiment are listed.

  It is a system that uses an accumulator Acc and a dedicated pump Pp2, and has a function to recover the potential energy and surplus flow rate and to recycle (power assist) the accumulator Acc reliably in all necessary circuits.

  The system configuration is adapted not only in the potential energy recovery mode but also in other modifications (reuse control valve 4).

  By rationally setting the regeneration function for the rod and the accumulator pressure by the dedicated pump Pp2, the responsiveness to the lowering operation command L during the recovery of potential energy is improved.

  Fuel efficiency can be improved.

  A function to variably set the flow rate ratio (with the main pump Pp1 flow rate) when the accumulated amount of accumulator is increased and the accumulated energy of the accumulator is reused, enabling continuous reuse when necessary. To do.

  This can contribute to miniaturization of equipment such as the main pump Pp1.

  To recover the main pump Pp1 surplus flow and reuse other than the potential energy recovery mode, the recovery control valve 2 and the reuse control valve 4 are connected to the pump discharge side to control their opening and main pump Pp1. It has a control function that can control the flow rate of the pump Pp2.

  In the potential energy recovery mode, the control valves 1, 3 and 5 and the flow rate of the dedicated pump Pp2 are controlled. In addition, the flow from the main pump Pp1 to the rod can be controlled to reduce the efficiency.

  Next, FIG. 2 is a flowchart showing the functions of the control device 8 in the control system having the accumulator Acc and the dedicated pump Pp2 as described above. The circled numbers in this figure indicate step numbers.

(Step 1)
An operation command L input from the operation lever is detected.

(Step 2)
From the operation command L, it is determined whether or not the lowering operation command for the potential energy recovery cylinder Cy1 such as the boom cylinder exceeds a set value.

(Step 3)
If the command for lowering the potential energy recovery cylinder Cy1 exceeds a certain set value, it is determined as the potential energy recovery mode regardless of whether there is an operation command for the circuit of the other circuit cylinder Cy2, and for lowering speed control during potential energy recovery. The opening degree of the provided recovery control valve 1 is adjusted according to the lowering operation command, and the recovery control valve 2 on the main pump side is closed.

  The recycle control valve 3 provided to secure the regenerative flow rate from the head side to the rod side of the potential energy recovery cylinder Cy1 (optionally, the regenerative control valve 5 with an opening degree adjusting function may be provided) is opened and closed. In response to the lowering command, the valve is opened and the regeneration flow rate is adjusted by the flow rate control function of the dedicated pump Pp2. In order to prevent the regenerative flow from leaking to the tank T via the pump flow rate control valve 7, the closing control valve 6 is closed by a lowering operation command.

(Step 4)
If it is determined that the circuit cylinder Cy2 other than the potential energy recovery cylinder Cy1 is the target, or if the potential energy recovery cylinder Cy1 is the target but is not in the potential energy recovery mode (NO in step 2), the operation command L Is less than or equal to a certain value C1.

(Step 5)
When the operation command L is equal to or less than a certain value C1, a control command for controlling the discharge flow rate from the main pump Pp1 and the opening area of the recovery control valve 2 is output, and recovery control from the main pump Pp1 is performed. .

(Step 6)
It is determined whether or not the operation command L is greater than a certain value C2 that is greater than the value C1.

(Step 7)
When the operation command L is greater than a certain value C2, the reuse control valve 4 is opened and a control command for controlling the injection flow rate from the dedicated pump Pp2 is output to reuse the potential energy accumulated in the accumulator Acc. Reuse control from the accumulator is performed.

(Step 8)
If any of Steps 2, 4 and 6 is NO, the operation command is between the value C1 and the value C2. At this time, the disconnection mode is set, the control valves 1 to 5 are closed, and the dedicated pump The flow rate of Pp2 is 0 output, and the flow rate of the main pump Pp1 is controlled normally.

  Next, the energy balance by reducing the accumulator pressure will be described.

  The energy balance by lowering the accumulator pressure Pa is positive (below (1), (3)) and minus (below (2), (4)), and the energy balance is the accumulator pressure Pa, Too low or too low. Therefore, it is reasonable to set the accumulator pressure Pa in a range that can satisfy the allowable accumulator volume, is low enough not to limit the recovery from the main pump Pp1, and that is reasonable in terms of energy balance.

  As the accumulator pressure Pa is reduced, the head pressure Ph also decreases. That is, the head pressure Ph = accumulator pressure Pa + ΔP, ΔP is mainly the pressure reduction in the recovery control valve 1 and is determined by the flow rate and the opening of the recovery control valve 1. The lower the head pressure Ph, the smaller the regeneration flow rate to the rod side required to achieve the same descending speed. In addition, in order to ensure speed and responsiveness, it is less necessary to discard the fluid from the head side into the tank and lower the head pressure Ph, so that more fluid can be stored in the accumulator Acc, and the accumulated energy in the accumulator Becomes big.

  However, at the initial stage of potential energy recovery, the loss due to the reduction in the head pressure Ph when communicating with the accumulator Acc increases due to the decrease in the accumulator pressure Pa.

  The recovery from the main pump Pp1 and the reuse thereof are advantageous in terms of energy balance because the bypass flow from the pump flow rate control valve 7 to the tank T is reduced. That is, when the flow rate discharged from the main pump Pp1 is controlled in accordance with the circuit required flow rate, the energy balance is the same because the assist amount at the time of injection is low as much as the recovery time is low, but it is discharged from the main pump Pp1 If the flow rate is controlled at the maximum flow rate within the constraints such as torque, the surplus is discharged to the tank T as a bypass flow, and in this case, the accumulation opportunity increases by reducing the accumulator pressure Pa. Therefore, the energy balance is advantageous accordingly.

  The power assist value when the accumulated potential energy is reused, that is, the product of the accumulator pressure Pa and the inlet flow rate of the dedicated pump Pp2 at the time of reuse, is reduced by the decrease of the accumulator pressure Pa.

  Next, the downsizing will be described.

  In order to enable downsizing, it is necessary to continuously supply the reuse flow rate from the accumulator Acc when necessary.

  If the accumulator Acc can reliably assist, for example, 20% when a large flow rate is required, the capacity of the main pump Pp1 can be reduced by that amount (for example, 20%).

  The engine E drives both the main pump Pp1 and the dedicated pump Pp2, so the amount of flow assist cannot be reduced. However, the required power of the dedicated pump Pp2 is reduced by the accumulator pressure Pa. The required power is reduced, and the dedicated pump Pp2 and the engine E can be reduced in size.

  Next, a system that does not need to increase the accumulator pressure Pa because it can be pressurized by the dedicated pump Pp2 when the potential energy is recovered and reused will be described.

  A variable flow type dedicated pump Pp2 such as a variable capacity type is provided so that a boosted flow rate can be flowed during reuse and a regenerative flow rate from the head side to the rod side can be flowed during the lowering operation. Thereby, it is not necessary to set the accumulator pressure Pa high in order to increase the available opportunity at the time of reusing potential energy, and the accumulator pressure Pa value can be set to a reasonable value. Therefore, the accumulator initial pressure Pa0 is set accordingly.

  A recovery control valve 1 is provided for lowering speed control at the time of recovering potential energy, and is used at the time of recovering potential energy.

  A recycle control valve 3 is provided to secure a regeneration flow path from the head side to the rod side of the potential energy recovery cylinder Cy1, and is used when recovering the potential energy. As an option, a regeneration control valve 5 with an opening adjustment function may be provided. The regeneration flow rate is controlled by the flow rate control function of the dedicated pump Pp2, and the reuse control valve 3 is basically based on an opening / closing operation.

  In order to prevent the regenerative flow from leaking, a closing control valve 6 is provided and used when recovering potential energy.

  Next, other points will be described.

  In addition to recovering not only the potential energy but also the excess flow rate, rationally setting the accumulator pressure Pa can improve the energy balance, improve the speed and responsiveness during the potential energy recovery operation, and improve productivity. The fuel efficiency of the engine can be improved by improving the fuel efficiency associated therewith, by reusing the stored energy, and at that time by operating the main pump Pp1 correspondingly to save energy.

  In the potential energy recovery mode, the system configuration can handle all of the operations of the potential energy recovery cylinder Cy1 other than the potential energy recovery mode and the operation of the other circuit cylinder Cy2.

  Other than during the recovery of potential energy, the flow path is set to pass through the existing pump flow rate control valve 7 as in the conventional control.

  Since the flow rate adjustment of the regeneration flow rate or the reuse flow rate can be performed by the dedicated pump Pp2, the reuse control valves 3 and 4 need only have an opening / closing function.

  Next, the effects of this embodiment will be listed.

  When the working fluid accumulated in the accumulator Acc is reused in the potential energy recovery cylinder Cy1, pressurization with the dedicated pump Pp2 is possible, so there is no need to set the accumulator pressure Pa high and within a reasonable range. The accumulator pressure Pa can be set to a low pressure, the working fluid can be easily accumulated in the accumulator Acc, and a high pressure can be obtained during reuse.

  Since the accumulator pressure Pa can be set to a low pressure by the dedicated pump Pp2, opening the recovery control valve 1 allows the potential energy recovery cylinder Cy1 to operate quickly with the accumulator pressure Pa as the load pressure, and the operating speed of the potential energy recovery cylinder Cy1. And responsiveness can be improved. In particular, the head pressure Ph at the time of lowering can be lowered, which is advantageous in securing the speed and responsiveness at the time of lowering operation.

  Part of the working fluid that flows out from the head side of the potential energy recovery cylinder Cy1 can be recycled to the rod side of the potential energy recovery cylinder Cy1 via the dedicated pump Pp2 by opening the reuse control valve 3. The pressure Pr can be made sufficiently higher than the head pressure Ph, and the operating speed and responsiveness of the potential energy recovery cylinder Cy1 can be further improved.

  When the working device 12 of the excavator 10 is moved up and down by the boom cylinder 14, the working fluid can be easily accumulated in the accumulator Acc, and a high pressure can be obtained during reuse.

  When the head pressure Ph is small, even when the rod pressure Pr and the head pressure Ph are substantially equal, speed and responsiveness can be easily ensured, so that the power consumption of the dedicated pump Pp2 when regenerating the potential energy can be reduced.

  The accumulator stored energy can be reused continuously during the required mode, such as excavation or lifting swivel. That is, an increase in the amount collected in the accumulator Acc and a flow rate ratio between the main pump flow rate and the accumulator flow rate when the accumulator stored energy is reused can be variably set, so that continuous reuse when necessary is possible.

  Fuel efficiency can be improved by efficient storage and reuse of recovered energy.

  By making use of the power assist capability of the accumulator Acc, equipment such as the main pump Pp1 and the engine E can be reduced in size and handled easily.

  The present invention is applicable to work machines such as hydraulic excavators and loaders.

It is a circuit diagram showing one embodiment of a fluid pressure control circuit according to the present invention. It is a flowchart which shows the function which the control apparatus of a circuit same as the above has. It is a side view of the working machine provided with the circuit same as the above.

Explanation of symbols

Pp1 main pump
Pp2 dedicated pump
Cy1 potential energy recovery cylinder
Acc Accumulator 1 Recovery control valve 3 Reuse control valve 9 Main circuit
10 Excavator
12 Working equipment
14 Boom cylinder as potential energy recovery cylinder

Claims (4)

A main circuit for controlling the working fluid discharged from the main pump and supplying it to the potential energy recovery cylinder;
An accumulator for accumulating the working fluid discharged from the potential energy recovery cylinder;
A fluid pressure control circuit comprising: a dedicated pump that sucks the working fluid discharged from the accumulator and supplies it to the potential energy recovery cylinder. The fluid pressure control circuit according to claim 1, further comprising a recovery control valve that controls a flow when the working fluid discharged from the potential energy recovery cylinder is recovered by the accumulator. The fluid pressure control circuit according to claim 1, further comprising a reuse control valve that controls a flow when the working fluid discharged from the dedicated pump is reused in the potential energy recovery cylinder. The fluid pressure control circuit according to any one of claims 1 to 3, wherein the potential energy recovery cylinder is a boom cylinder that rotates a working device of a hydraulic excavator in a vertical direction.

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