Fluid circuit

Abstract

To provide a fluid circuit which can stabilize a flow of a work fluid flown into an actuator.SOLUTION: When a first pressure PA detected by a first pressure detector 9 is larger than a value in which a predefined pressure α is added to a second pressure PB detected by a second pressure detector 10 (PA>PB+α), a supply flow amount of a fluid supply device is lowered from a first target flow amount Q1 to a second target flow amount Q2 which is smaller than the first target flow amount Q1 based on a differential pressure ΔPAB of the first pressure PA and the second pressure PB, and a variable throttle valve 9 is opened. When a value in which the predefined pressure α to the differential pressure ΔPAB is smaller than a predefined threshold value β (ΔPAB+α<β), the supply flow amount of the fluid supply device 2 is recovered to the first target flow amount Q1, and an opening area of the variable throttle valve 9 is closed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a fluid circuit comprising a fluid supply and an accumulator. [Background technology]

[0002] In various fields, fluid circuits are known that use a hydraulic fluid such as hydraulic oil delivered from a fluid supply device such as a pump to drive an actuator. Some of these fluid circuits include an accumulator that can store pressurized hydraulic fluid, and can be controlled based on the pressure on the fluid supply device side and the pressure on the accumulator side.

[0003] For example, the fluid circuit disclosed in Patent Document 1 includes a flow path extending from a pump to an accumulator. A switching valve is provided in the flow path between the pump and the accumulator. A first pressure detector is also provided in the flow path between the switching valve and the accumulator, and a second pressure detector is provided between the pump and the switching valve.

[0004] The switching valve can be switched between a check state, which allows the working fluid to pass from the pump side to the accumulator side, and an open state, which allows the working fluid to pass in both directions. When the increased fluid pressure is to be accumulated in the accumulator, the check state allows the working fluid delivered by the pump to be stored in the accumulator. When the working fluid stored in the accumulator is to be used, the open state allows the working fluid to be delivered from the accumulator to the pump side. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 10-175459 (pages 5 and 6, Figure 1) Summary of the Invention [Problem to be solved by the invention]

[0006] To save energy, a fluid supply device and an accumulator may operate in cooperation. In a fluid circuit such as that described in Patent Document 1, the flow rate of the working fluid discharged from the accumulator can be adjusted by controlling the aperture of a switching valve based on the differential pressure between the pressure detected by a first pressure detector and the pressure detected by a second pressure detector. However, when the switching valve is open, the working fluid can pass in both directions between the pump and the accumulator. This can lead to a risk of the flow of the working fluid flowing into the actuator becoming unstable, especially when the differential pressure between the pump discharge pressure and the accumulated pressure in the accumulator is small.

[0007] The present invention has been made in view of these problems, and has as its object to provide a fluid circuit that can stabilize the flow of working fluid flowing into an actuator. [Means for solving the problem]

[0008] In order to solve the above problems, the fluid circuit of the present invention comprises: a fluid supply device that delivers the working fluid; and an accumulator that accumulates the pressurized working fluid; a variable throttle valve and the accumulator are disposed in a branch flow path branching from a main flow path extending from the fluid supply device to the actuator; a first pressure detector is provided between the variable throttle valve and the accumulator, and a second pressure detector is provided in the branch flow path between the main flow path and the variable throttle valve, and the variable throttle valve can be controlled based on the pressure detected by these detectors; The branch passage is provided with a check valve. According to this, in the open state in which the variable throttle valve is open and the working fluid is sent from the accumulator to the main flow path, the check valve prevents the working fluid sent from the fluid supply device from flowing into the accumulator side, and if the differential pressure obtained by subtracting the pressure on the fluid supply device side from the pressure on the accumulator side is below a predetermined value, the movement of working fluid from the accumulator to the fluid supply device side is restricted, thereby stabilizing the flow of working fluid flowing into the actuator.

[0009] The check valve may be provided between the first pressure detector and the second pressure detector. According to this, when the differential pressure between the accumulator side and the fluid supply device side relative to the check valve is small, the flow from the accumulator to the fluid supply device side is stopped by the check valve, thereby preventing the effects of subtle fluctuations in the working fluid from affecting the first pressure detector and improving its detection accuracy.

[0010] The check valve may be provided between the variable throttle valve and the first pressure detector. This makes it possible to prevent the first pressure detector from being affected by pressure fluctuations and pressure losses caused by the operation of the variable throttle valve. [Brief explanation of the drawings]

[0011] [Figure 1] 1 is a schematic diagram showing a fluid circuit according to a first embodiment of the present invention. [Figure 2] 4A and 4B are diagrams for explaining the characteristics of a variable throttle valve. [Figure 3] 1 is a diagram for explaining the relationship between the amount of working fluid delivered to a hydraulic cylinder, the amount of working fluid delivered by a pump, and the amount of working fluid delivered by an accumulator. FIG. [Figure 4] 3 is a schematic diagram of a branch flow path in the first embodiment when the variable throttle valve is in a closed state. FIG. [Figure 5] 3 is a schematic diagram of a branch flow path in the first embodiment when the variable throttle valve is in an open state. FIG. [Figure 6]10 is a schematic diagram illustrating a case where the pressure difference between branch flow paths is small when the variable throttle valve is in an open state in the first embodiment. FIG. [Figure 7] FIG. 10 is a schematic diagram showing the main parts of a fluid circuit according to a second embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A fluid circuit according to an embodiment of the present invention will be described below with reference to the accompanying drawings. [Example]

[0013] A fluid circuit according to a first embodiment will be described with reference to FIGS.

[0014] As shown in Fig. 1, the fluid circuit can be applied to hydraulic devices such as actuators, brakes, steering, and transmissions in passenger cars and work vehicles such as trucks, hydraulic excavators, forklifts, cranes, and garbage trucks. Note that the hydraulic circuit shown in Fig. 1 is one example of the fluid circuit of the present invention, and is not limited to the configuration shown in Fig. 1.

[0015] The fluid circuit of this embodiment is generally configured to use hydraulic pressure to operate a hydraulic cylinder 5 as an actuator to move the workpiece W.

[0016] The fluid circuit is mainly composed of a variable displacement hydraulic pump 2 as a fluid supply device, a switching valve 3, a hydraulic remote control valve 4, a hydraulic cylinder 5, an accumulator 6, a first pressure detector 7, a check valve 8, a proportional electromagnetic throttle valve 9 as a variable throttle valve, a second pressure detector 10, a controller C, and various oil passages.

[0017] The hydraulic pump 2 is connected to a drive mechanism 1 such as a vehicle engine or an electric motor. As a result, the hydraulic pump 2, driven by power from the drive mechanism 1, delivers pressurized oil to a main oil passage 20, which serves as a main flow path.

[0018] The pressure oil delivered from the hydraulic pump 2 flows into the switching valve 3 through a main oil passage 20 and an oil passage 21 that is branched and connected to the main oil passage 20 .

[0019] The switching valve 3 is a 6-port, 3-position, open-center type switching valve. When the switching valve 3 is in the neutral position, it connects the oil line 21 to the tank-side oil line 30 and the tank T. Therefore, all of the pressure oil delivered from the hydraulic pump 2 is discharged to the tank T.

[0020] Furthermore, the switching valve 3 in the extension position 3E connects the main oil passage 20 to a head-side oil passage 50 (hereinafter simply referred to as the head-side oil passage 50) in the hydraulic cylinder 5. At the same time, the switching valve 3 connects a rod-side oil passage 51 (hereinafter simply referred to as the rod-side oil passage 51) in the hydraulic cylinder 5 to the tank-side oil passage 31 and the tank T.

[0021] Moreover, the switching valve 3 in the retracted position 3S connects the main oil passage 20 to the rod side oil passage 51 in the hydraulic cylinder 5. At the same time, the switching valve 3 connects the head side oil passage 50 to the tank side oil passage 31 and the tank T.

[0022] The hydraulic remote control valve 4 is a variable pressure reducing valve. The hydraulic remote control valve 4 reduces the pressure oil of pilot primary pressure delivered from a pilot hydraulic pump (not shown) to pilot secondary pressure according to the amount of operation of the operating lever 4-1. The pilot primary pressure oil here refers to the pressure oil delivered from the pilot circuit hydraulic pump. The pilot secondary pressure oil passes through signal oil passages 40 and 41 and acts on the signal ports 3-1 and 3-2 of the switching valve 3.

[0023] The operation of the hydraulic cylinder 5 in response to operation of the hydraulic remote control valve 4 will now be described. When the operating lever 4-1 is operated in the extension direction E, the switching valve 3 is switched to the extension position 3E. Then, pressure oil delivered from the hydraulic pump 2 flows into the head chamber 5-1 of the hydraulic cylinder 5 through the head-side oil passage 50 connected to the main oil passage 20. At the same time, pressure oil flowing out of the rod chamber 5-2 is discharged into the tank T through the tank-side oil passage 31 connected to the rod-side oil passage 51. This allows the hydraulic cylinder 5 to be extended and the workpiece W to be lifted.

[0024] Furthermore, when the operating lever 4-1 is operated in the retraction direction S, the switching valve 3 is switched to the retraction position 3S. Then, the pressurized oil delivered from the hydraulic pump 2 flows into the rod chamber 5-2 in the hydraulic cylinder 5 through the rod-side oil passage 51 connected to the main oil passage 20. At the same time, the pressurized oil flowing out from the head chamber 5-1 is discharged into the tank T through the tank-side oil passage 31 connected to the head-side oil passage 50. This allows the hydraulic cylinder 5 to be retracted and the workpiece W to be lowered.

[0025] Furthermore, a relief flow path 23, which is connected to a tank T, is branched off from the main oil path 20 upstream of the check valve 22. A relief valve 24 is disposed midway along the relief flow path 23. When the pressure in the main oil path 20 becomes abnormally high, the relief valve 24 opens. This allows the pressurized oil to be discharged from the relief flow path 23 to the tank T.

[0026] Further, a branch oil passage 60 as a branch flow passage is branched and connected to the main oil passage 20 upstream of the check valve 22 .

[0027] The branch oil passage 60 is made up of oil passages 61, 62, 63, and 64. More specifically, the branch oil passage 60 is connected in the following order from the main oil passage 20 side: oil passage 61, proportional electromagnetic throttle valve 9, oil passage 62, check valve 8, oil passage 63, accumulator 6, and oil passage 64.

[0028] Furthermore, the oil passage 64 is connected to the head chamber 5-1 of the hydraulic cylinder 5 via a check valve 65 and a switching valve (not shown). This allows the accumulator 6 to accumulate pressurized oil delivered from the head chamber 5-1 in response to the contraction of the hydraulic cylinder 5. Note that the means for accumulating pressure in the accumulator 6 may be something other than the hydraulic cylinder 5, such as a hydraulic pump.

[0029] The proportional electromagnetic throttle valve 9 is connected to the controller C by an electric signal line 11. As shown in Fig. 2, when no signal is input from the controller C, the proportional electromagnetic throttle valve 9 is in a closed state where the oil passages 61, 62 are not in communication. When a signal is input from the controller C, the proportional electromagnetic throttle valve 9 is in an open state where the oil passages 61, 62 are in communication. When in the open state, the proportional electromagnetic throttle valve 9 opens more in a quadratic curve as the signal input from the controller C becomes larger, for example, as the voltage becomes higher.

[0030] 1, a second pressure detector 10 is disposed in an oil passage 61 connecting the main oil passage 20 and the proportional electromagnetic throttle valve 9. A first pressure detector 7 is disposed in an oil passage 63 connecting the check valve 8 and the accumulator 6.

[0031] The first pressure detector 7 is connected to the controller C by an electric signal line 12. The first pressure detector 7 transmits a signal PA indicating the detected pressure on the accumulator 6 side to the controller C. The second pressure detector 10 is connected to the controller C by an electric signal line 13. The second pressure detector 10 transmits a signal PB indicating the detected pressure on the main oil passage 20 side to the controller C.

[0032] The controller C is connected to the flow rate control unit of the hydraulic pump 2 by an electric signal line 14. The controller C is capable of adjusting the delivery rate of the hydraulic pump 2. The controller C is also connected to the control unit of the drive mechanism 1 of the hydraulic pump 2 by an electric signal line 15.

[0033] The drive source for operating the hydraulic cylinder 5 may be the hydraulic pump 2 alone, the accumulator 6 alone, or the hydraulic pump 2 and the accumulator 6 working together. In the following explanation, an example in which the hydraulic pump 2 and the accumulator 6 work together to extend the hydraulic cylinder 5 will be described with reference to Figures 1 to 5.

[0034] Referring to Figure 3, when the hydraulic remote control valve 4 is operated to the maximum extent in the extension direction E, the switching valve 3 switches to the extension position 3E at time t1. As a result, as shown by the solid line in Figure 3, pressurized oil is delivered from the hydraulic pump 2 to the hydraulic cylinder 5 at a substantially constant flow rate Q1. Note that the driving conditions of the hydraulic pump 2 do not change before and after time t1, and before time t1, the pressurized oil from the hydraulic pump 2 is delivered to the tank T through the oil passage 30.

[0035] After the switching valve 3 switches to the extension position 3E, if the controller C determines that the pressure PA on the accumulator 6 side is greater than the value obtained by adding a predetermined pressure α to the pressure PB on the main oil passage 20 side (PA>PB+α), it determines that the accumulator 6 can be used.

[0036] When the accumulator 6 is available, the controller C outputs a signal to the hydraulic pump 2 to reduce the flow rate to the target flow rate Q2 based on the differential pressure ΔPAB between the pressure PA and the pressure PB and the load L of the hydraulic cylinder 5, and also outputs a signal to the proportional electromagnetic throttle valve 9 to open it.

[0037] As a result, the delivery rate of the hydraulic pump 2 gradually decreases over time according to the response characteristics of the hydraulic pump 2, as indicated by the dotted line between times t2 and t3 in Figure 3. After time t3 when the delivery rate of the hydraulic pump 2 reaches the target flow rate Q2, the delivery rate of the hydraulic pump 2 becomes a substantially constant flow rate Q2.

[0038] Furthermore, the controller C switches the proportional electromagnetic throttle valve 9 from the closed state shown in Fig. 4 to the throttled open state (hereinafter simply referred to as the open state) shown in Fig. 5. The opening of the proportional electromagnetic throttle valve 9 at this time is adjusted in accordance with the reduced flow rate of the hydraulic pump 2 and the differential pressure ΔPAB.

[0039] For example, to supply pressurized oil from the accumulator 6 at a flow rate corresponding to the reduced flow rate of the hydraulic pump 2, the opening area of ​​the proportional electromagnetic throttle valve 9 can be determined using the differential pressure ΔPAB so that the pressure PB on the main oil passage 20 side is maintained at approximately the same constant pressure after time t2 as between times t1 and t2.

[0040] The method of supplying pressurized oil from the accumulator 6 at a flow rate corresponding to the reduced flow rate of the hydraulic pump 2 is not limited to maintaining the pressure PB on the main oil passage 20 side substantially constant, but may also be a method of determining the opening area of ​​the proportional electromagnetic throttle valve 9 using the response characteristics of the hydraulic pump 2 that are stored in advance.

[0041] Here, the response characteristics of the proportional electromagnetic throttle valve 9 are sufficiently better than the response characteristics of the hydraulic pump 2, so by controlling the opening area of ​​the proportional electromagnetic throttle valve 9 in accordance with the operating state of the hydraulic pump 2 as described above, the flow rate supplied to the main oil passage 20 can be controlled with high precision.

[0042] As a result, pressurized oil is sent from the accumulator 6 through the oil passage 63 , the check valve 8 , the oil passage 62 , the proportional electromagnetic throttle valve 9 and the oil passage 61 to the main oil passage 20 .

[0043] Thereafter, at time t4, when the value obtained by adding the differential pressure ΔPAB to a predetermined pressure α becomes smaller than a predetermined threshold value β (ΔPAB+α<β), the controller C outputs a signal to return the hydraulic pump 2 to the target flow rate Q1 and also outputs a signal to the proportional electromagnetic throttle valve 9 to reduce the opening area and cause it to become blocked.

[0044] After time t4, the opening area of ​​the proportional electromagnetic throttle valve 9 is reduced so as to supply a flow rate according to the response characteristics of the hydraulic pump 2. This makes it possible to maintain the pressure PB on the main oil passage 20 side approximately constant after time t4, as it was between times t1 and t4. Then, at time t5, the proportional electromagnetic throttle valve 9 enters the closed state shown in FIG.

[0045] In this way, the amount of pressure oil delivered from the accumulator 6 to the main oil passage 20 is adjusted, as shown by the diagonal hatching in Fig. 3. As a result, as shown by the solid line in Fig. 3, the amount and pressure PB of pressure oil delivered to the hydraulic cylinder 5 become substantially the same as those when pressure oil is delivered only by the hydraulic pump 2.

[0046] Furthermore, in this embodiment, the opening of the proportional electromagnetic throttle valve 9 is adjusted based on the pressure detected by the pressure detectors 7, 10, making it possible to arbitrarily control the amount of oil sent from the accumulator 6 to the main oil passage 20. Therefore, compared to a configuration in which an on-off valve is provided instead of the proportional electromagnetic throttle valve 9, for example, a large amount of pressurized oil does not flow into the main oil passage 20 when the proportional electromagnetic throttle valve 9 is switched. This makes it possible to prevent abnormalities such as shocks caused by abrupt changes in the operating speed of the hydraulic cylinder 5, thereby allowing the hydraulic cylinder 5 to operate smoothly.

[0047] Here, when the proportional electromagnetic throttle valve 9 is in an open state, if the amount of pressure stored in the accumulator 6 decreases and the pressure difference ΔPAB becomes small, the pressure oil on the main oil line 20 side may flow into the oil line 61 due to the flow on the main oil line 20 side or the pulsation of the pressure oil delivered from the hydraulic pump 2, but as shown in Fig. 6, the check valve 8 closes and prevents the pressure oil on the main oil line 20 side from flowing into the accumulator 6 side. At this time, the check valve 8 is acted upon by the biasing force of the spring 8k which biases the valve body in the closing direction, so the check valve 8 is reliably closed.

[0048] Furthermore, the check valve 8 is subjected to the biasing force of the spring 8k that biases the valve element in the closing direction, so when the differential pressure ΔPAB approaches zero while the proportional electromagnetic throttle valve 9 is open, in other words when the differential pressure ΔPAB falls to a predetermined level or less, the check valve 8 reliably closes as shown in Figure 6, making it less likely for chattering to occur in the check valve 8. This makes it easier to stabilize the control of the hydraulic pump 2 and accumulator 6 working together.

[0049] As a result, even if the pressure difference ΔPAB becomes small, the flow of pressure oil flowing into the hydraulic cylinder 5 can be stabilized.

[0050] The above-described control by the controller C when the hydraulic pump 2 and the accumulator 6 are operating in cooperation with each other is merely an example, and may be modified as appropriate.

[0051] As described above, in the fluid circuit of this embodiment, the check valve 8 is arranged between the pressure detectors 7 and 10, and when the pressure difference between the pressure on the accumulator 6 side in the oil passage 63 and the pressure on the hydraulic pump 2 side in the oil passage 62 relative to the check valve 8 is small, the flow from the oil passage 63 to the oil passage 62 is stopped by the check valve 8, thereby preventing the effects of slight fluctuations in the pressure oil from affecting the first pressure detector 7 and improving the detection accuracy.

[0052] Furthermore, the check valve 8 is disposed between the proportional electromagnetic throttle valve 9 and the first pressure detector 7. Therefore, even if pressure fluctuations and pressure losses occur when the proportional electromagnetic throttle valve 9 is switched from a closed state to an open state or from an open state to a closed state, the differential pressure between the accumulator 6 side and the proportional electromagnetic throttle valve 9 side of the check valve 8 does not reach a differential pressure sufficient to open the check valve 8, and therefore the effects of the pressure fluctuations and pressure losses on the first pressure detector 7 can be prevented. [Example]

[0053] A fluid circuit according to the second embodiment will be described with reference to Fig. 7. Note that a description of the same configuration as in the first embodiment will be omitted.

[0054] 7, in the second embodiment, a branch oil passage 160 serving as a branch flow path of the fluid circuit is made up of oil passages 161, 162, 163, and 64. More specifically, the branch oil passage 160 is connected in the following order from the main oil passage 20 side: oil passage 161, check valve 8, oil passage 162, proportional electromagnetic throttle valve 9, oil passage 163, accumulator 6, and oil passage 64. A second pressure detector 10 is disposed in oil passage 161, and a first pressure detector 7 is disposed in oil passage 163.

[0055] In this way, since the check valve 8 is arranged between the second pressure detector 10 and the proportional electromagnetic throttle valve 9, when the pressure difference between the pressure on the accumulator 6 side in the oil passage 162 and the pressure on the hydraulic pump 2 side in the oil passage 161 is small relative to the check valve 8, the flow from the oil passage 162 to the oil passage 161 is stopped by the check valve 8, thereby preventing the effect of slight fluctuations in the pressure oil from affecting the first pressure detector 7 and improving the detection accuracy.

[0056] Although the embodiments of the present invention have been described above with reference to the drawings, the specific configuration is not limited to these embodiments, and the present invention also includes modifications and additions that do not deviate from the gist of the present invention.

[0057] For example, in the first and second embodiments, the working fluid is oil, but the working fluid is not limited to oil and may be any fluid, and may be changed as appropriate.

[0058] Furthermore, in the first and second embodiments, the hydraulic pump is driven before and after a series of operations to extend the hydraulic cylinder, and the amount of pressurized oil delivered from the hydraulic pump is described as being approximately constant per unit time. However, this is not limiting, and the drive amount of the hydraulic pump may be increased after receiving a command to perform the extension operation, for example, the hydraulic pump may be moved from a stopped state to an operating state, or may be changed from a low-load operating state to a high-load operating state.

[0059] In addition, in the above-described first and second embodiments, a check valve is disposed between the first pressure detector and the second pressure detector, but this is not limited to this, and a check valve may be disposed between the main oil passage and the second pressure detector.

[0060] In addition, in the first and second embodiments, a single check valve is disposed between the proportional electromagnetic throttle valve and the first pressure detector or between the proportional electromagnetic throttle valve and the second pressure detector, but this is not limiting and multiple check valves may be disposed in the branch oil passage. For example, a check valve may be disposed between the proportional electromagnetic throttle valve and the first pressure detector, and between the proportional electromagnetic throttle valve and the second pressure detector, or between the first pressure detector and the second pressure detector, and at another location in the branch oil passage. [Explanation of symbols]

[0061] 2 hydraulic pumps 5 Hydraulic cylinder (actuator) 6 Accumulator 7. First pressure detector 8 Check valve 9 Proportional electromagnetic throttle valve (variable throttle valve) 10 Second pressure detector 20 Main oil passage (main flow path) 60 Branch oil passage (branch flow path) 160 Branch oil passage (branch flow passage) L load Q1,Q2 Target flow rate PA Accumulator side pressure PB Main flow path pressure ΔPAB differential pressure t1 time t2 time t3 time t4 time t5 time t6 time

Claims

1. a fluid supply device that delivers the working fluid; and an accumulator that accumulates the pressurized working fluid; a variable throttle valve and the accumulator are disposed in a branch flow path branching from a main flow path extending from the fluid supply device to the actuator; a first pressure detector is provided between the variable throttle valve and the accumulator, and a second pressure detector is provided in the branch flow path between the main flow path and the variable throttle valve, and the variable throttle valve can be controlled based on pressure detected by these detectors; A fluid circuit in which a check valve is provided in the branch flow path.

2. 2. The fluid circuit according to claim 1, wherein the check valve is provided between the first pressure detector and the second pressure detector.

3. 3. The fluid circuit according to claim 1, wherein the check valve is provided between the variable throttle valve and the first pressure detector.

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