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 including a fluid supply device and an accumulator.

Background Art

[0002] In various fields, fluid circuits that drive an actuator using a working fluid such as hydraulic oil sent out from a fluid supply device such as a pump are known. Some of these fluid circuits include an accumulator capable of accumulating the pressurized working 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 shown 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. Also, a first pressure detector is 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 valve state that allows the passage of the working fluid from the pump side to the accumulator side and an open state that allows the passage of the working fluid in both directions. When accumulating the pressurized fluid pressure in the accumulator, the check valve state is set so that the working fluid sent out by the pump is accumulated in the accumulator. Also, when using the working fluid accumulated in the accumulator, the state is switched to the open state so that the working fluid is sent out from the accumulator to the pump side.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] From an energy-saving perspective, a fluid supply device and an accumulator are sometimes used in cooperation. In a fluid circuit like the one described in Patent Document 1, the flow rate of the working fluid delivered from the accumulator can be adjusted by controlling the opening of a switching valve based on the pressure difference between the pressure detected by the first pressure detector and the pressure detected by the second pressure detector. However, when the switching valve is open, the working fluid can pass in both directions between the pump and the accumulator. As a result, the flow and pressure of the working fluid in the main flow path may push the working fluid in the branch flow path back in the opposite direction or draw it in the forward direction, which could cause the flow of the working fluid flowing into the actuator to become unstable. In particular, when the pressure difference between the discharge pressure of the pump and the accumulated pressure of the accumulator is small, there was a risk that the flow of the working fluid flowing into the actuator would become unstable.

[0007] This invention was made in view of these problems, and aims to provide a fluid circuit that can stabilize the flow of working fluid into an actuator. [Means for solving the problem]

[0008] To solve the aforementioned problems, the fluid circuit of the present invention is: It comprises a fluid supply device for delivering working fluid and an accumulator for storing the pressurized working fluid, A variable throttle valve and the accumulator are arranged in a branch channel that branches off from the main channel 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 branched flow path between the main flow path and the variable throttle valve, and the fluid circuit is capable of controlling the variable throttle valve based on the pressure detected by these detection units. A check valve is provided in the aforementioned branch channel. According to this, in the open state where the variable throttle valve is opened and 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. Furthermore, 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 level, the movement of working fluid from the accumulator to the fluid supply device side is restricted, thereby stabilizing the flow of working fluid 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 pressure difference between the accumulator side and the fluid supply device side is small relative to the check valve, the flow from the accumulator to the fluid supply device side is stopped by the check valve. This prevents subtle fluctuations in the working fluid from affecting the first pressure detector, thereby improving its detection accuracy.

[0010] The check valve may be provided between the variable throttle valve and the first pressure detector. According to this, it is possible to prevent the effects of pressure fluctuations and pressure loss caused by the operation of the variable throttle valve from affecting the first pressure detector. [Brief explanation of the drawing]

[0011] [Figure 1] This is a schematic diagram showing the fluid circuit of Example 1 according to the present invention. [Figure 2] This is a diagram illustrating the characteristics of a variable throttle valve. [Figure 3] This diagram illustrates the relationship between the amount of working fluid delivered to the hydraulic cylinder, the amount of working fluid delivered by the pump, and the amount of working fluid delivered by the accumulator. [Figure 4] This is a schematic diagram of the branched channel in Example 1 where the variable throttle valve is in a closed state. [Figure 5] This is a schematic diagram of the branched channel in Example 1 where the variable throttle valve is in the open state. [Figure 6]It is a schematic diagram for explaining the case where the pressure difference in the branch flow path is small in the open state of the variable throttle valve in Example 1. [Figure 7] It is a schematic diagram showing the main part of the fluid circuit of Example 2 according to the present invention.

Mode for Carrying Out the Invention

[0012] A mode for carrying out the fluid circuit according to the present invention will be described below based on examples.

Example

[0013] The fluid circuit according to Example 1 will be described with reference to FIGS. 1 to 6.

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

[0015] The fluid circuit of this example generally has a configuration in which a hydraulic cylinder 5 as an actuator is operated using hydraulic pressure to move a work W.

[0016] The fluid circuit mainly consists 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 each oil passage.

[0017] The hydraulic pump 2 is connected to a drive mechanism 1 such as a vehicle engine or an electric motor. Thus, the hydraulic pump 2 driven by the power from the drive mechanism 1 sends pressure oil to a main oil passage 20 as a main flow path.

[0018] The pressurized oil sent out from the hydraulic pump 2 flows into the switching valve 3 through the main oil passage 20 and the oil passage 21 branched and connected to the main oil passage 20.

[0019] The switching valve 3 is a 6-port 3-position type open center type switching valve. The switching valve 3 in the neutral position connects the oil passage 21 to the tank side oil passage 30 and the tank T. Therefore, the entire amount of the pressurized oil sent out from the hydraulic pump 2 is discharged into the tank T.

[0020] Also, the switching valve 3 in the extended position 3E connects the main oil passage 20 to the 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 the 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] Also, 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 type pressure reducing valve. The hydraulic remote control valve 4 reduces the pressure of the pilot primary pressure pressurized oil sent out from a pilot hydraulic pump (not shown) to a pilot secondary pressure according to the operation amount of the operation lever 4-1. The pilot primary pressure pressurized oil here refers to the pressurized oil sent out from the pilot circuit hydraulic pump. The pilot secondary pressure pressurized oil acts on the signal ports 3-1 and 3-2 of the switching valve 3 through the signal oil passages 40 and 41.

[0023] The operation of the hydraulic cylinder 5 in response to the operation of the hydraulic remote control valve 4 will now be explained. 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, the pressurized oil sent 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, the pressurized oil that has flowed out from the rod chamber 5-2 is discharged to the tank T through the tank-side oil passage 31 connected to the rod-side oil passage 51. As a result, the hydraulic cylinder 5 can be extended and the workpiece W can be lifted.

[0024] Furthermore, when the operating lever 4-1 is operated in the retraction direction S, the switching valve 3 switches to the retraction position 3S. Then, the pressurized oil sent from the hydraulic pump 2 flows into the rod chamber 5-2 of 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 that has flowed 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 passage 23, connected to tank T, branches off from the main oil passage 20 upstream of the check valve 22. A relief valve 24 is located in the middle of the relief passage 23. When the pressure in the main oil passage 20 becomes abnormally high, the relief valve 24 is released. As a result, the pressurized oil is discharged from the relief passage 23 to tank T.

[0026] Furthermore, a branch oil passage 60 is connected to the main oil passage 20 upstream of the check valve 22, serving as a branch channel.

[0027] The branched oil passage 60 consists of oil passages 61, 62, 63, and 64. More specifically, the branched 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 store pressurized oil delivered from the head chamber 5-1 in response to the contraction operation of the hydraulic cylinder 5. Note that the means for accumulating pressure in the accumulator 6 may be other than the hydraulic cylinder 5, for example, a hydraulic pump.

[0029] The proportional electromagnetic throttle valve 9 is connected to the controller C by an electrical signal line 11. As shown in Figure 2, when no signal is input from the controller C, the proportional electromagnetic throttle valve 9 is in a closed state, with the oil passages 61 and 62 not connected. When a signal is input from the controller C, the proportional electromagnetic throttle valve 9 is in an open state, with the oil passages 61 and 62 connected. Furthermore, in the open state, the proportional electromagnetic throttle valve 9 opens in a quadratic curve as the signal input from the controller C is larger, for example, as the voltage increases.

[0030] Returning to Figure 1, a second pressure detector 10 is located in the oil passage 61 connecting the main oil passage 20 and the proportional electromagnetic throttle valve 9. A first pressure detector 7 is located in the 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 electrical signal line 12. The first pressure detector 7 transmits the detected pressure PA signal from the accumulator 6 to the controller C. The second pressure detector 10 is connected to the controller C by an electrical signal line 13. The second pressure detector 10 transmits the detected pressure PB signal from the main oil passage 20 to the controller C.

[0032] Controller C is connected to the flow control unit of the hydraulic pump 2 via an electrical signal line 14. Controller C can adjust the output volume of the hydraulic pump 2. Controller C is also connected to the control unit of the drive mechanism 1 of the hydraulic pump 2 via an electrical 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 cooperation of the hydraulic pump 2 and the accumulator 6. In the following description, an example of extending the hydraulic cylinder 5 by the cooperation of the hydraulic pump 2 and the accumulator 6 will be explained with reference to Figures 1 to 5.

[0034] Referring to Figure 3, when the hydraulic remote control valve 4 is operated to its 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 at a nearly constant flow rate Q1 is supplied from the hydraulic pump 2 to the hydraulic cylinder 5. Note that the driving conditions of the hydraulic pump 2 remain unchanged around time t1, and before time t1, the pressurized oil from the hydraulic pump 2 is sent to the tank T through the oil passage 30.

[0035] After the switching valve 3 switches to the extended position 3E, 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), and determines that the accumulator 6 can be used.

[0036] If 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 pressure PA and 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.

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

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

[0039] For example, in order 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 by using the differential pressure ΔPAB to maintain the pressure PB on the main oil passage 20 side at approximately the same constant pressure as between time t1 and t2, even after time t2.

[0040] Furthermore, the method for 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 at a substantially constant level, but may also involve determining the opening area of ​​the proportional electromagnetic throttle valve 9 using the response characteristics of the hydraulic pump 2 that have been stored in advance.

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

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

[0043] Subsequently, at time t4, when the value obtained by adding a predetermined pressure α to the differential pressure ΔPAB becomes smaller than a predetermined threshold β (ΔPAB + α < β), 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 its opening area and cause it to close.

[0044] From time t4 onward, the opening area of ​​the proportional electromagnetic throttle valve 9 is reduced to supply a flow rate corresponding to the response characteristics of the hydraulic pump 2. This allows the pressure PB on the main oil passage 20 side to remain approximately constant from time t4 onward, compared to the pressure between time t1 and t4. Then, at time t5, the proportional electromagnetic throttle valve 9 enters the closed state shown in Figure 4.

[0045] In this way, as shown by the hatched lines in Figure 3, the amount of pressurized oil sent from the accumulator 6 to the main oil passage 20 is adjusted. As a result, as shown by the solid line in Figure 3, the amount of pressurized oil and pressure PB sent to the hydraulic cylinder 5 become approximately the same as when the oil is supplied only by the hydraulic pump 2.

[0046] Furthermore, in this embodiment, the opening degree of the proportional electromagnetic throttle valve 9 is adjusted based on the pressure detected by the pressure detectors 7 and 10, allowing for arbitrary control of the amount of oil delivered from the accumulator 6 to the main oil passage 20. Therefore, compared to a configuration in which, for example, an on-off valve is provided instead of the proportional electromagnetic throttle valve 9, 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 prevents abnormalities such as shocks caused by abrupt changes in the operating speed of the hydraulic cylinder 5, and thus allows the hydraulic cylinder 5 to operate smoothly.

[0047] Here, when the proportional electromagnetic throttle valve 9 is open, the amount of pressure accumulated in the accumulator 6 decreases and the differential pressure ΔPAB becomes small. In this case, due to the flow on the main oil passage 20 side and the pulsation of the pressurized oil sent from the hydraulic pump 2, pressurized oil from the main oil passage 20 side may flow into the oil passage 61. However, as shown in Figure 6, the check valve 8 closes, preventing pressurized oil from the main oil passage 20 side from flowing into the accumulator 6 side. At this time, the check valve 8 is subjected to the biasing force of the spring 8k that biases the valve body in the closing direction, so the check valve 8 is ensured to close reliably.

[0048] Furthermore, since the check valve 8 is subjected to the biasing force of the spring 8k that biases the valve body in the closing direction, when the differential pressure ΔPAB approaches zero in the open state of the proportional electromagnetic throttle valve 9, in other words, when the differential pressure ΔPAB falls below a predetermined level, the check valve 8 closes reliably as shown in Figure 6, and the check valve 8 is less likely to chatter. As a result, the coordinated control of the hydraulic pump 2 and the accumulator 6 is more stable.

[0049] These features allow the flow of pressurized oil into the hydraulic cylinder 5 to be stabilized even when the differential pressure ΔPAB becomes small.

[0050] Furthermore, the control of the hydraulic pump 2 and accumulator 6 by controller C during their coordinated operation is merely an example and may be modified as appropriate.

[0051] As described above, in this embodiment, the fluid circuit has a check valve 8 positioned between the pressure detectors 7 and 10. 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 is small relative to the check valve 8, the flow from the oil passage 63 to the oil passage 62 is stopped by the check valve 8. This prevents subtle fluctuations in pressurized oil from affecting the first pressure detector 7, thereby improving its detection accuracy.

[0052] Furthermore, the check valve 8 is positioned between the proportional electromagnetic throttle valve 9 and the first pressure detector 7. Therefore, even if pressure fluctuations and pressure losses occur when switching the proportional electromagnetic throttle valve 9 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 of the check valve 8 and the proportional electromagnetic throttle valve 9 side will not reach a differential pressure sufficient to open the check valve 8. Thus, the effects of pressure fluctuations and pressure losses on the first pressure detector 7 can be prevented. [Examples]

[0053] The fluid circuit according to Example 2 will be described with reference to Figure 7. Note that the description of components that are identical to those in Example 1 and therefore redundant will be omitted.

[0054] As shown in Figure 7, in this embodiment 2, the branch oil passage 160, which serves as a branch flow path for the fluid circuit, consists 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. The second pressure detector 10 is located in oil passage 161, and the first pressure detector 7 is located in oil passage 163.

[0055] Thus, since the check valve 8 is positioned 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. This prevents subtle fluctuations in pressurized oil from affecting the first pressure detector 7, thereby improving its detection accuracy.

[0056] Although embodiments of the present invention have been described above with reference to the drawings, the specific configurations are not limited to these embodiments, and any changes or additions that do not depart from the spirit of the present invention are also included.

[0057] For example, in the above-described embodiments 1 and 2, the working fluid was assumed to be oil, but it is not limited to this; any fluid will suffice, and it may be changed as appropriate.

[0058] Furthermore, in the above embodiments 1 and 2, 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, the system is not limited to this configuration, and the amount of drive of the hydraulic pump may be increased after receiving a command for extension, for example, by starting the hydraulic pump from a stopped state or changing from a low-load operating state to a high-load operating state.

[0059] Furthermore, although the above-described embodiments 1 and 2 assumed a configuration in which a check valve is placed between the first pressure detector and the second pressure detector, the configuration is not limited to this, and the check valve may be placed between the main oil passage and the second pressure detector.

[0060] Furthermore, in the above embodiments 1 and 2, the check valve was described as being located as a single unit between the proportional electromagnetic throttle valve and the first pressure detector, or between the proportional electromagnetic throttle valve and the second pressure detector. However, the configuration is not limited to this, and multiple check valves may be located in the branched oil passage. For example, they may be located between the proportional electromagnetic throttle valve and the first pressure detector, and between the proportional electromagnetic throttle valve and the second pressure detector, respectively, or between the first pressure detector and the second pressure detector, and elsewhere in the branched oil passage. [Explanation of symbols]

[0061] 2. Hydraulic pump 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 Branching oil passage (branching channel) 160 Branch oil passage (branch channel) 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

[Claim 1] A fluid supply device that delivers working fluid to a main channel connected to an actuator, An accumulator is provided in a branch channel that branches off from the main channel, A variable throttle valve is provided in the branch channel between the main channel and the accumulator, Equipped with, A fluid circuit is provided in which a first pressure detector is provided in the branch channel between the variable throttle valve and the accumulator, a second pressure detector is provided in the branch channel between the main channel and the variable throttle valve, and a controller is provided to control the fluid supply device and the variable throttle valve based on the pressure detection results of the first and second pressure detectors. The branching channel between the variable throttle valve and the first pressure detector is provided with a check valve that allows the working fluid to flow from the accumulator side to the variable throttle valve side and prevents the working fluid from flowing back from the variable throttle valve side to the accumulator side. When the first pressure detected by the first pressure detector is greater than the value obtained by adding a predetermined pressure to the second pressure detected by the second pressure detector, the controller reduces the supply flow rate of the fluid supply device from a first target flow rate to a second target flow rate smaller than the first target flow rate, based on the differential pressure between the first pressure and the second pressure, and opens the variable throttle valve. The controller is a fluid circuit that, when the value obtained by adding the differential pressure to the predetermined pressure falls below a predetermined threshold, restores the supply flow rate of the fluid supply device to the first target flow rate and closes the opening area of ​​the variable throttle valve.

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