Hydraulic pump performance degradation detection system

Abstract

To provide a performance lowering detection system of a hydraulic pump which can detect the lowering of the performance of the hydraulic pump without using a flowmeter.SOLUTION: A performance lowering detection system 1A of a hydraulic pump of the present embodiment includes a variable capacity type hydraulic pump 22, a selector valve 4 connected to the hydraulic pump 22 by a pump line 41, and a regulator 3 for making a capacity of the hydraulic pump 22 variable according to a command current, and limiting the capacity of the hydraulic pump 22 to a limit value when the discharge pressure of the hydraulic pump 22 exceeds a set value. Also, the performance lowering detection system 1A includes a control device 8 for sending and supplying the command current to the regulator 3, and a pressure sensor 71 for measuring the discharge pressure of the hydraulic pump 22. The control device 7 determines whether or not the performance of the hydraulic pump 22 is lowered on the basis of a current value of the command current and the discharge pressure of the hydraulic pump 22 which is measured by the pressure sensor 71 at the non-operation of a hydraulic actuator 5.SELECTED DRAWING: Figure 1

Description

Technical Field

[0006] , ,

[0005] ,

[0007] , ,

[0001] The present disclosure relates to a system for detecting a performance degradation of a hydraulic pump.

Background Art

[0002] Conventionally, a hydraulic circuit that supplies hydraulic fluid from a hydraulic pump to a hydraulic actuator has been known. In such a hydraulic circuit, it is desirable to detect a performance degradation of the hydraulic pump.

[0003] For example, Patent Document 1 discloses an apparatus that measures a drain flow rate from a hydraulic pump with a flow meter and determines whether the hydraulic pump is worn based on the drain flow rate.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, since the drain flow rate is small, the measured value of the flow meter is easily affected by the measurement accuracy. Therefore, it is difficult to detect a performance degradation of the hydraulic pump, such as a slight decrease in the discharge flow rate due to wear of the sliding portion of the hydraulic pump, based on the drain flow rate measured by the flow meter.

[0006] Therefore, an object of the present disclosure is to provide a hydraulic pump performance degradation detection system that can detect a performance degradation of a hydraulic pump without using a flow meter.

Means for Solving the Problems

[0007] This disclosure provides a hydraulic pump performance degradation detection system comprising: a variable displacement hydraulic pump; a switching valve connected to the hydraulic pump by a pump line and to a hydraulic actuator by a supply / discharge line, which blocks the pump line when the hydraulic actuator is not operating; a regulator that changes the capacity of the hydraulic pump according to a command current and limits the capacity of the hydraulic pump to a limit value when the discharge pressure of the hydraulic pump exceeds a set value; a control device that supplies the command current to the regulator; and a pressure sensor that measures the discharge pressure of the hydraulic pump, wherein the control device determines whether the performance of the hydraulic pump has deteriorated when the hydraulic actuator is not operating, based on the current value of the command current and the discharge pressure of the hydraulic pump measured by the pressure sensor.

[0008] This disclosure provides a hydraulic pump performance degradation detection system comprising: a hydraulic cylinder that extends to press against a workpiece; a hydraulic pump connected to the hydraulic cylinder by a pair of supply and discharge lines to form a closed circuit; an electric motor that drives the hydraulic pump; a control device that controls the electric motor; and a pressure sensor that measures the discharge pressure of the hydraulic pump when the hydraulic cylinder is extended. The control device adjusts the rotational speed of the electric motor so that the discharge pressure of the hydraulic pump measured by the pressure sensor becomes a set value when the hydraulic cylinder is pressing against the workpiece, records the adjusted rotational speed as a determination rotational speed, and determines whether the performance of the hydraulic pump has deteriorated by comparing the currently recorded determination rotational speed with determination rotational speeds recorded in the past. [Effects of the Invention]

[0009] According to this disclosure, a decrease in the performance of a hydraulic pump can be detected without using a flow meter. [Brief explanation of the drawing]

[0010] [Figure 1] This is a schematic diagram of the hydraulic pump performance degradation detection system according to the first embodiment. [Figure 2]This graph shows the relationship between the commanded current to the regulator and the discharge pressure of the hydraulic pump. [Figure 3] This is a schematic diagram of the hydraulic pump performance degradation detection system according to the second embodiment. [Modes for carrying out the invention]

[0011] <First Embodiment> Figure 1 shows a hydraulic pump performance degradation detection system 1A according to the first embodiment. For example, the hydraulic pump performance degradation detection system 1A can be used in industrial machinery such as steelmaking machinery.

[0012] Specifically, the hydraulic pump performance degradation detection system 1A includes a variable-displacement hydraulic pump 22, a regulator 3 that changes the capacity of the hydraulic pump 22, and a switching valve 4 interposed between the hydraulic pump 22 and the hydraulic actuator 5. In the illustrated example, there is one hydraulic actuator 5, but there may be multiple hydraulic actuators 5. In this case, there will also be multiple switching valves 4.

[0013] In this embodiment, the hydraulic actuator 5 is a double-acting hydraulic cylinder 51. Therefore, the switching valve 4 is a three-position valve. However, the hydraulic actuator 5 may be a hydraulic motor. Alternatively, the hydraulic actuator 5 may be a single-acting cylinder and the switching valve 4 may be a two-position valve.

[0014] The hydraulic pump 22 is connected to the switching valve 4 by the pump line 41. The switching valve 4 is connected to the tank by the tank line 42 and to the hydraulic actuator 5 by a pair of supply and discharge lines 43 and 44. A relief line branches off from the pump line 41, and a relief valve is provided on this relief line.

[0015] The switching valve 4 is in a neutral position when the hydraulic actuator 5 is not operating, and when switched from the neutral position to the first operating position or the second operating position, the hydraulic actuator 5 operates in the first or second direction.

[0016] In this embodiment, the switching valve 4 blocks all of the pump line 41, tank line 42, and supply / discharge line 44 in the neutral position. However, depending on the application of the hydraulic actuator 5 or the hydraulic circuit, the pump line 41 may be blocked in the neutral position while the supply / discharge lines 43 and 44 communicate with the tank line 42. In the first operating position, i.e., the right position in Figure 1, the switching valve 4 connects the pump line 41 to the supply / discharge line 43 and the supply / discharge line 44 to the tank line 42. In the second operating position, i.e., the left position in Figure 1, the switching valve 4 connects the pump line 41 to the supply / discharge line 44 and the supply / discharge line 43 to the tank line 42.

[0017] In this embodiment, the hydraulic pump 22 is driven at a constant rotational speed by an electric motor 21. The electric motor 21 is controlled by a control device 7. The rotational speed of the hydraulic pump 22 is, for example, within the range of 1000 to 1800 rpm. However, the hydraulic pump 22 may also be driven by an engine.

[0018] Furthermore, in this embodiment, the hydraulic pump 22 is a swash plate pump having a swash plate 22a, which is an axial piston pump. However, the hydraulic pump 22 may be a swash shaft pump, which is another type of axial piston pump. Alternatively, the hydraulic pump 22 may be another type of pump, such as a vane pump.

[0019] The regulator 3 receives a command current from the control device 7. The regulator 3 changes the capacity q of the hydraulic pump 22, i.e., the discharge amount per revolution, according to the command current. In this embodiment, the regulator 3 increases the capacity q of the hydraulic pump 22 as the command current increases. Also, in this embodiment, the minimum capacity of the hydraulic pump 22 is zero. However, the minimum capacity of the hydraulic pump 22 may be set to a value greater than zero.

[0020] Furthermore, in the present embodiment, as shown in FIG. 2, when the discharge pressure Pd of the hydraulic pump 22 exceeds the set value Pc, the regulator 3 restricts the capacity of the hydraulic pump 22 to the limit value qc. This is so-called cutoff. This cutoff is performed mechanically, rather than by the control of the control device 7.

[0021] More specifically, the regulator 3 includes an electromagnetic proportional valve 38, a flow control piston 36, and a cutoff piston 37. The electromagnetic proportional valve 38 is connected to the auxiliary pump 23 by the primary pressure line 24. The auxiliary pump 23 is driven by the electric motor 21 together with the hydraulic pump 22.

[0022] The electromagnetic proportional valve 38 outputs a secondary pressure corresponding to the command current supplied to the regulator 3. In the illustrated example, the electromagnetic proportional valve 38 is a direct proportional type in which the command current and the secondary pressure show a positive correlation, but the electromagnetic proportional valve 38 may be an inverse proportional type in which the command current and the secondary pressure show a negative correlation.

[0023] The flow control piston 36 changes the capacity q of the hydraulic pump 22 according to the secondary pressure of the electromagnetic proportional valve 38. When the discharge pressure Pd of the hydraulic pump 22 exceeds the set value Pc, the cutoff piston 37 restricts the capacity q of the hydraulic pump 22 to the limit value qc, giving priority to the flow control piston 36.

[0024] Furthermore, in addition to the electromagnetic proportional valve 38, the flow control piston 36, and the cutoff piston 37, the regulator 3 includes a servo piston 31 connected to the swash plate 22a of the hydraulic pump 22, and an adjustment valve 32 for driving the servo piston 31.

[0025] The regulator 3 is formed with a first pressure receiving chamber 3a into which the discharge pressure Pd of the hydraulic pump 22 is introduced, and a second pressure receiving chamber 3b into which the control pressure is introduced. The servo piston 31 has a first end portion exposed to the first pressure receiving chamber 3a and a second end portion having a larger diameter than the first end portion and exposed to the second pressure receiving chamber 3b.

[0026] The regulating valve 32 adjusts the control pressure introduced into the second pressure-receiving chamber 3b. Specifically, the regulating valve 32 includes a spool 33 that moves in a capacity-increasing direction, which decreases the control pressure, and a capacity-decreasing direction, which increases the control pressure, and a sleeve 34 that houses the spool 33. The capacity-increasing direction is the direction of movement to the left in Figure 1, and the capacity-decreasing direction is the direction of movement to the right in Figure 1.

[0027] The sleeve 34 is connected to the servo piston 31 by a feedback lever 35. The sleeve 34 has a pump port, a tank port, and an output port. The pump port communicates with the pump line 41, the tank port communicates with the tank, and the output port communicates with the second pressure-receiving chamber 3b.

[0028] The spool 33 is biased in the capacity-increasing direction by a spring and pushed in the capacity-decreasing direction by a flow control piston 36 and a cutoff piston 37. The flow control piston 36 pushes the spool 33 via a lever 36a, and the cutoff piston 37 pushes the spool 33 via a lever 37a. When the spool 33 is pushed by the flow control piston 36 or the cutoff piston 37 and moves in the capacity-decreasing direction against the biasing force of the spring, the opening area between the pump port and the communication port of the sleeve 34 increases and the opening area between the tank port and the communication port decreases. When it is biased by the spring and moves in the capacity-increasing direction, the opening area between the pump port and the communication port of the sleeve 34 decreases and the opening area between the tank port and the communication port increases.

[0029] In this embodiment, the spool 33 is pushed in the capacity-reducing direction by the retraction of the flow control piston 36 and the advancement of the cutoff piston 37. However, whether the flow control piston 36 and the cutoff piston 37 advance or retract when pushing the spool 33 in the capacity-reducing direction can be changed as appropriate. The flow control piston 36 and the cutoff piston 37 are configured such that the one that limits the capacity to a smaller value, i.e., commands a smaller capacity, takes priority in pushing the spool 33. Since this configuration is known technology, a detailed explanation is omitted.

[0030] Depending on the relative positional relationship between the sleeve 34 and the spool 33, the output port of the sleeve 34 communicates with either the pump port or the tank port, or with one of them. When the spool 33 moves in the direction of increasing or decreasing capacity, the relative positional relationship between the spool 33 and the sleeve 34 is determined so that the forces acting on both sides of the servo piston 31 are balanced, and the control pressure is adjusted. The forces acting on both sides of the servo piston 31 are obtained by multiplying the pressure by the pressure received by the pressure-receiving area of ​​the servo piston 31.

[0031] Furthermore, the regulator 3 has an operating chamber 3c formed therein that applies the secondary pressure of the electromagnetic proportional valve 38 to the flow control piston 36. In other words, the flow control piston 36 moves forward when the secondary pressure of the electromagnetic proportional valve 38 increases and moves backward when the secondary pressure decreases.

[0032] Furthermore, the regulator 3 has an operating chamber 3d that applies the discharge pressure Pd of the hydraulic pump 22 to the cutoff piston 37. In other words, the cutoff piston 37 moves forward when the discharge pressure Pd of the hydraulic pump 22 becomes higher than a set value Pc set by the spring 39, and moves backward when the discharge pressure Pd becomes lower than the set value Pc.

[0033] With respect to the control device 7 described above, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, dedicated processors, integrated circuits, ASICs (Application Specific Integrated Circuits), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuits. In this disclosure, a circuit, unit, or means is hardware that performs the enumerated functions, or hardware programmed to perform the enumerated functions. The hardware may be hardware disclosed herein, or other known hardware that is programmed or configured to perform the enumerated functions. If the hardware is a processor, which is considered a type of circuit, then the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or the processor.

[0034] The control device 7 is electrically connected to a pressure sensor 71 located in the pump line 41 and a tachometer 72 located on the electric motor 21. Note that in Figure 1, some signal lines are omitted for the sake of simplicity. The pressure sensor 71 measures the discharge pressure Pd of the hydraulic pump 22, and the tachometer 72 measures the rotational speed of the electric motor 21.

[0035] The control device 7 performs a performance check on the hydraulic pump 22 when the hydraulic actuator 5 is not operating, that is, when the hydraulic pump 22 is not supplying hydraulic fluid to the hydraulic actuator 5. On the other hand, when a performance check on the hydraulic pump 22 is not performed, the control device 7 sends a command current to the regulator 3 such that the capacity q of the hydraulic pump 22 is maximized.

[0036] When performing a performance check on the hydraulic pump 22, the control device 7 first controls the regulator 3 so that the capacity q of the hydraulic pump 22 is minimized. Specifically, the command current supplied to the regulator 3 is set to zero. However, the control device 7 may also supply a standby current greater than zero as the command current to the regulator 3 so as to maintain the capacity q of the hydraulic pump 22 at its minimum.

[0037] When the pump line 41 is blocked by the switching valve 4, as shown in Figure 2, when the hydraulic pump 22 is driven at a relatively low capacity, the discharge pressure Pd of the hydraulic pump 22 does not become very high due to internal leaks in the hydraulic pump 22, etc. In this embodiment, in addition to internal leaks in the hydraulic pump 22, there are also leaks in the switching valve 4.

[0038] In that state, the control device 7 determines whether the performance of the hydraulic pump 22 has deteriorated based on the current value of the command current to the regulator 3 and the discharge pressure Pd of the hydraulic pump 22 measured by the pressure sensor 71.

[0039] More specifically, as shown in Figure 2, the control device 7 increases the command current to the regulator 3 from a predetermined value Is, and stores the current value when the discharge pressure Pd of the hydraulic pump 22 measured by the pressure sensor 71 reaches the threshold Pt, in other words, when the discharge pressure Pd of the hydraulic pump 22 rises to the threshold Pt, as the determination current value It. In this embodiment, the predetermined value Is is zero.

[0040] As shown in Figure 2, as the command current to the regulator 3 increases, the capacity q of the hydraulic pump 22 increases, but the discharge pressure Pd of the hydraulic pump 22 is almost zero as long as the amount of working fluid discharged from the hydraulic pump 22 is small. When the discharge of working fluid from the hydraulic pump 22 increases slightly, the discharge pressure Pd of the hydraulic pump 22 rises, and the drain flow rate Qdr also increases. Since the high-pressure seal portion of the hydraulic pump 22 has a nearly constant gap, the amount of leakage does not change significantly even when the discharge pressure Pd rises. Therefore, the discharge pressure Pd rises rapidly. When the discharge pressure Pd exceeds the set value Pc mentioned above, the cutoff piston 37 is activated, and the capacity q is limited to the limit value qc.

[0041] As described above, the threshold value Pt may be smaller than the cut-off set value Pc as shown in FIG. 2, or may be equal to the set value Pc. When the threshold value Pt is equal to the set value Pc, the current value It is equal to the current value Ic at which the cut-off starts. However, since the discharge pressure Pd rises rapidly as described above, it is easy to set the threshold value Pt to the set value Pc.

[0042] The control device 7 stores a reference current value I0 in advance. The reference current value I0 is the current value of the command current when the discharge pressure Pd of the hydraulic pump 22 reaches the threshold value Pt when there is no abnormality in the hydraulic pump 22. As the reference current value I0, the current value of the command current when the discharge pressure Pd of the hydraulic pump 22 reaches the threshold value Pt, which can be obtained more simply by performing a performance check on the pump alone, may also be used. For example, as a case where there is no abnormality in the hydraulic pump 22, the reference current value I0 may be obtained before factory shipment after a short operation after the hydraulic drive device including the hydraulic pump 22 is attached to the industrial machine, or at a time when the operation time is short immediately after factory shipment after the completion of the industrial machine.

[0043] The control device 7 compares the stored determination current value It with the reference current value I0. When the determination current value It is greater than or equal to the set value V larger than the reference current value I0, that is, when It - I0 ≥ V, it is determined that the low performance of the hydraulic pump 22 has deteriorated. On the other hand, when the determination current value It is not greater than or equal to the set value V larger than the reference current value I0, that is, when It - I0 < V, the control device 7 determines that the low performance of the hydraulic pump 22 has not deteriorated.

[0044] When the command current to the regulator 3 is increased to increase the capacity of the hydraulic pump 22 from a relatively small capacity, the current value at which the discharge pressure Pd of the hydraulic pump 22 reaches a threshold Pt changes depending on the degree of abnormality of the hydraulic pump 22. In this embodiment, if the hydraulic pump 22 is a swashplate pump, abnormalities in the hydraulic pump 22 include, for example, wear of the shoe that slides against the swashplate at the tip of the piston, or wear of the sliding surface between the valve plate and the cylinder block. Therefore, by using the current value of the command current to the regulator 3 and the discharge pressure Pd of the hydraulic pump 22, as in this embodiment, it is possible to detect a decrease in the performance of the hydraulic pump 22 without using a flow meter. Moreover, it is possible to detect a decrease in the performance of the hydraulic pump 22 with higher accuracy than by measuring the drain flow rate.

[0045] Furthermore, by simply replacing the regulator of the hydraulic system installed in existing industrial machinery with the regulator 3 described above, and adding the control device 7 described above to the existing control device, it becomes possible to verify the performance of the hydraulic pump. Moreover, under normal circumstances when performance verification of the hydraulic pump 22 is not performed, the capacity q of the hydraulic pump 22 can be kept at its maximum while the capacity limiting by the cutoff piston 37 can be activated.

[0046] <Variation> In the above embodiment, when the current value at which the discharge pressure Pd of the hydraulic pump 22 reaches the threshold Pt is stored as the determination current value It, the control device 7 increases the command current to the regulator 3 to increase the capacity q of the hydraulic pump 22 from a relatively small capacity. Conversely, the control device 7 may decrease the command current to the regulator 3 to decrease the capacity of the hydraulic pump 22 from a relatively large capacity, and store the current value at which the discharge pressure Pd of the hydraulic pump 22, measured by the pressure sensor 71, falls to the threshold Pt as the determination current value It. Even when the capacity q of the hydraulic pump 22 is decreased from a relatively large capacity, the current value at which the discharge pressure Pd of the hydraulic pump 22 reaches the threshold Pt changes depending on the degree of abnormality of the hydraulic pump 22. Therefore, even in this case, by using the current value of the command current to the regulator 3 and the discharge pressure Pd of the hydraulic pump 22, it is possible to detect the performance degradation of the hydraulic pump 22 without using a flow meter.

[0047] Furthermore, the regulator 3 may be configured to reduce the capacity of the hydraulic pump 22 as the command current increases. In this case as well, when the current value at which the discharge pressure Pd of the hydraulic pump 22 reaches the threshold Pt is stored as the determination current value It, the control device 7 may either decrease the command current to the regulator 3 to increase the capacity q of the hydraulic pump 22 from a relatively small capacity, or increase the command current to the regulator 3 to decrease the capacity q of the hydraulic pump 22 from a relatively large capacity.

[0048] <Second Embodiment> Figure 3 shows the hydraulic pump performance degradation detection system 1B according to the second embodiment. For example, the hydraulic pump performance degradation detection system 1B is used in industrial machinery such as press machines. In this embodiment, the same reference numerals are used for the same components as in the first embodiment, and redundant explanations are omitted.

[0049] In this embodiment as well, the hydraulic pump 22 is of variable displacement type. However, in this embodiment, the hydraulic pump 22 is of two-position switching type. Depending on the industrial machine, the hydraulic pump 22 may be of fixed displacement type.

[0050] In this embodiment, the hydraulic pump 22 supplies working fluid to the hydraulic cylinder 51, which is a double-acting cylinder that extends to press against the workpiece. The hydraulic cylinder 51 presses against the workpiece via a pressing member attached to the rod of the hydraulic cylinder 51. In the case of a press machine, the pressing member is a die. For example, the extension direction of the hydraulic cylinder 51 is vertically downward.

[0051] The electric motor 21 that drives the hydraulic pump 22 is, for example, a servo motor. In this case, the control device 7 may include the function of a servo amplifier, or a servo amplifier may be provided between the control device 7 and the electric motor 21.

[0052] Furthermore, in this embodiment, as described above, since the hydraulic pump 22 is a two-position switching type, a regulator 3A is employed to change the capacity of the hydraulic pump 22 between a first capacity and a second capacity smaller than the first capacity. For example, the regulator 3A may include a servo piston 31 having a first end exposed to the first pressure-receiving chamber 3a and a second end exposed to the second pressure-receiving chamber 3b, as shown in Figure 1, and a switching valve that switches whether the second pressure-receiving chamber 3b is connected to the pump line 41 or to the tank.

[0053] Furthermore, in this embodiment, the hydraulic pump 22 is a bidirectional pump that can rotate in both directions. That is, the hydraulic pump 22 has a first port and a second port, and when it rotates in one direction, the first port becomes the suction port and the second port becomes the discharge port, and when it rotates in the opposite direction, the second port becomes the suction port and the first port becomes the discharge port.

[0054] The bidirectional hydraulic pump 22 is connected to the hydraulic cylinder 51 by a pair of supply and discharge lines 81 and 82 to form a closed circuit. More specifically, supply and discharge line 81 is connected to the head side of the hydraulic cylinder 51, and supply and discharge line 82 is connected to the rod side of the hydraulic cylinder 51.

[0055] The supply and discharge line 81 is connected to the tank by a replenishment line 91, which is equipped with a check valve. Similarly, the supply and discharge line 82 is connected to the tank by a replenishment line 92, which is also equipped with a check valve. In addition, a relief line 93, equipped with a relief valve 94, is connected to each of the supply and discharge lines 81 and 82.

[0056] A check valve 83 is provided in the supply and discharge line 82 on the rod side, and a bypass line 84 is connected to bypass the check valve 83. A relief valve 85 is provided in the bypass line 84. The check valve 83 allows flow from the hydraulic pump 22 to the rod side of the hydraulic cylinder 51, but prohibits flow in the reverse direction.

[0057] A pressure sensor 73 is provided in the supply and discharge line 81. In other words, the pressure sensor 73 measures the discharge pressure Pd of the hydraulic pump 22 when the hydraulic cylinder 51 is extended. The control device 7 is electrically connected to the pressure sensor 73. Note that in Figure 3, some signal lines are omitted for the sake of simplifying the drawing. Furthermore, the control device 7 is electrically connected to a tachometer 72 that measures the rotational speed of the electric motor 21, as in the first embodiment, and is also electrically connected to a stroke sensor 74 provided on the hydraulic cylinder 51. The stroke sensor 74 measures the stroke of the rod of the hydraulic cylinder 51.

[0058] The control device 7 receives a first operation signal, which is an extension command for the hydraulic cylinder 51, and a second operation signal, which is a shortening command for the hydraulic cylinder 51. The control device 7 controls the electric motor 21 and the regulator 3A based on the first and second operation signals.

[0059] First, when the control device 7 receives the first operation signal, the control device 7 controls the regulator 3A so that the capacity of the hydraulic pump 22 becomes the first, larger capacity. Then, the control device 7 rotates the electric motor 21 in a direction that causes the hydraulic pump 22 to discharge working fluid through the supply and discharge line 81 towards the head side of the hydraulic cylinder 51. When the rod-side pressure of the hydraulic cylinder 51 exceeds the set pressure of the relief valve 85, the hydraulic cylinder 51 extends at high speed. The speed of the hydraulic cylinder 51 is determined by the flow rate pushed in from the head side.

[0060] When the stroke measured by the stroke sensor 74 reaches a predetermined value, the control device 7 controls the regulator 3A so that the capacity of the hydraulic pump 22 becomes a smaller second capacity. As a result, the hydraulic cylinder 51 extends slowly while the rod-side pressure of the hydraulic cylinder 51 is maintained at the set pressure of the relief valve 85.

[0061] Subsequently, when the pressing member comes into contact with the workpiece and the hydraulic cylinder 51 begins to press the workpiece via the pressing member, the discharge pressure Pd of the hydraulic pump 22 increases. While the hydraulic cylinder 51 is pressing the workpiece, the control device 7 adjusts the rotation speed of the electric motor 21 so that the discharge pressure Pd of the hydraulic pump 22, as measured by the pressure sensor 73, reaches a set value.

[0062] In this embodiment, the control device 7 performs a performance check on the hydraulic pump 22 while the hydraulic cylinder 51 is pressing against the workpiece. Specifically, the control device 7 records the rotational speed of the electric motor 21, which has been adjusted so that the discharge pressure Pd of the hydraulic pump 22 is a set value, as the determination rotational speed N. Then, the control device 7 compares the determination rotational speed Nn recorded this time with a determination rotational speed Np recorded in the past to determine whether the performance of the hydraulic pump 22 has deteriorated. For example, the determination rotational speed Np recorded in the past may be from one year ago or several years ago.

[0063] For example, the control device 7 determines that the performance of the hydraulic pump 22 has deteriorated if the current rotational speed Nn is greater than or equal to a predetermined value than the previous rotational speed Np, and determines that the performance of the hydraulic pump 22 has not deteriorated if the current rotational speed Nn is not greater than or equal to a predetermined value than the previous rotational speed Np.

[0064] In this embodiment, the rotational speed of the electric motor 21 changes depending on the degree of abnormality in the hydraulic pump 22, in order to maintain the discharge pressure Pd of the hydraulic pump 22 at a set pressure when pressing the workpiece. Therefore, by using the rotational speed of the electric motor 21 and the discharge pressure Pd of the hydraulic pump 22, it is possible to detect a decrease in the performance of the hydraulic pump 22 without using a flow meter. Moreover, it is possible to detect a decrease in the performance of the hydraulic pump 22 with higher accuracy than by measuring the drain flow rate. Furthermore, it is possible to detect a decrease in the performance of the hydraulic pump 22 while machining the workpiece according to the normal process, and since no special process is required, no extra downtime is generated.

[0065] When a second operation signal is input to the control device 7, the control device 7 rotates the electric motor 21 in a direction that causes the hydraulic pump 22 to discharge working fluid through the supply and discharge line 82 toward the rod side of the hydraulic cylinder 51. This shortens the hydraulic cylinder 51.

[0066] <Other Embodiments> This disclosure is not limited to the embodiments described above, and various modifications are possible without departing from the gist of this disclosure.

[0067] <Summary> In a first aspect, the present disclosure provides a hydraulic pump performance degradation detection system comprising: a variable displacement hydraulic pump; a switching valve connected to the hydraulic pump by a pump line and to a hydraulic actuator by a supply / discharge line, which blocks the pump line when the hydraulic actuator is not operating; a regulator that changes the capacity of the hydraulic pump according to a command current and limits the capacity of the hydraulic pump to a limit value when the discharge pressure of the hydraulic pump exceeds a set value; a control device that supplies the command current to the regulator; and a pressure sensor that measures the discharge pressure of the hydraulic pump, wherein the control device determines whether the performance of the hydraulic pump has deteriorated based on the current value of the command current and the discharge pressure of the hydraulic pump measured by the pressure sensor when the hydraulic actuator is not operating.

[0068] With the above configuration, when the pump line is blocked by the switching valve, the discharge pressure of the hydraulic pump will not be very high when the hydraulic pump is driven at a relatively low capacity, due to internal leaks in the hydraulic pump, etc. On the other hand, by changing the command current supplied to the regulator to increase the capacity of the hydraulic pump from a relatively low capacity or decrease it from a relatively high capacity, the current value at which the discharge pressure of the hydraulic pump reaches a threshold will change depending on the degree of abnormality of the hydraulic pump. Therefore, by using the current value of the command current to the regulator and the discharge pressure of the hydraulic pump, it is possible to detect a decrease in the performance of the hydraulic pump without using a flow meter. Moreover, it is possible to detect a decrease in the performance of the hydraulic pump with higher accuracy than by measuring the drain flow rate.

[0069] In a second embodiment, in the first embodiment, for example, the control device may change the command current when the hydraulic actuator is not operating, store the current value when the discharge pressure of the hydraulic pump measured by the pressure sensor reaches a threshold value as a determination current value, compare the stored determination current value with a pre-stored reference current value, and determine that the performance of the hydraulic pump has deteriorated if the determination current value is greater than or equal to a set value than the reference current value.

[0070] In a third embodiment, in the second embodiment, for example, the regulator may increase the capacity of the hydraulic pump as the command current increases, and the control device may increase the command current from a predetermined value when storing the current value when the discharge pressure of the hydraulic pump measured by the pressure sensor reaches the threshold as a determination current value.

[0071] In a fourth embodiment, in the third embodiment, the regulator includes an electromagnetic proportional valve that outputs a secondary pressure corresponding to the command current, a flow control piston that changes the capacity of the hydraulic pump according to the secondary pressure of the electromagnetic proportional valve, and a cutoff piston that, when the discharge pressure of the hydraulic pump exceeds the set value, takes precedence over the flow control piston and limits the capacity of the hydraulic pump to the limit value, and the control device may, when not performing a performance check on the hydraulic pump, send a command current to the regulator such that the capacity of the hydraulic pump is maximized. With this configuration, it becomes possible to perform a performance check on the hydraulic pump simply by replacing the regulator in a hydraulic system mounted on an existing industrial machine and adding the above control device in addition to the existing control device. Moreover, under normal circumstances when a performance check on the hydraulic pump is not performed, the capacity of the hydraulic pump can be kept at its maximum while the capacity limiting by the cutoff piston can be activated.

[0072] In a fifth aspect, the present disclosure provides a hydraulic pump performance degradation detection system comprising: a hydraulic cylinder that extends to press a workpiece; a hydraulic pump connected to the hydraulic cylinder by a pair of supply and discharge lines to form a closed circuit; an electric motor that drives the hydraulic pump; a control device that controls the electric motor; and a pressure sensor that measures the discharge pressure of the hydraulic pump when the hydraulic cylinder is extended, wherein the control device adjusts the rotational speed of the electric motor so that the discharge pressure of the hydraulic pump measured by the pressure sensor becomes a set value when the hydraulic cylinder is pressing the workpiece, records the adjusted rotational speed as a determination rotational speed, and determines whether the performance of the hydraulic pump has deteriorated by comparing the determination rotational speed recorded this time with determination rotational speeds recorded in the past.

[0073] With the above configuration, the rotation speed of the electric motor changes depending on the degree of malfunction in the hydraulic pump, in order to maintain the hydraulic pump's discharge pressure at the set pressure when pressing the workpiece. Therefore, by using the rotation speed of the electric motor and the discharge pressure of the hydraulic pump, it is possible to detect a decrease in the hydraulic pump's performance without using a flow meter. Moreover, it is possible to detect a decrease in the hydraulic pump's performance with higher accuracy than by measuring the drain flow rate. Furthermore, it is possible to detect a decrease in the hydraulic pump's performance while machining the workpiece according to the normal process, and since no special process is required, no extra downtime is incurred. [Explanation of Symbols]

[0074] 1A, 1B Hydraulic Pump Performance Degradation Detection System 21 Electric motor 22 Hydraulic pump 3 Regulator 31 Servo Piston 36 Flow control piston 37 Cut-off piston 38 Solenoid proportional valve 4. Switching valve 41 Pump Line 5. Hydraulic actuator 51 Hydraulic cylinder 7 Control device 71,73 Pressure Sensor 72 Tachometer 81,82 Supply and discharge lines

Claims

1. Variable displacement hydraulic pump, A switching valve is connected to the hydraulic pump by a pump line and to a hydraulic actuator by a supply / discharge line, and blocks the pump line when the hydraulic actuator is not operating. A regulator that changes the capacity of the hydraulic pump according to the command current, and limits the capacity of the hydraulic pump to a limit value when the discharge pressure of the hydraulic pump exceeds a set value, A control device that supplies the commanded current to the regulator, The system includes a pressure sensor for measuring the discharge pressure of the hydraulic pump, The regulator includes an electromagnetic proportional valve that outputs a secondary pressure corresponding to the command current, a flow control piston that changes the capacity of the hydraulic pump according to the secondary pressure of the electromagnetic proportional valve, and a cutoff piston that, when the discharge pressure of the hydraulic pump exceeds the set value, takes precedence over the flow control piston and limits the capacity of the hydraulic pump to the limit value. The control device is a hydraulic pump performance degradation detection system that determines whether the performance of the hydraulic pump has deteriorated based on the current value of the command current and the discharge pressure of the hydraulic pump measured by the pressure sensor when the hydraulic actuator is not operating.

2. The control device changes the command current when the hydraulic actuator is not operating, stores the current value when the discharge pressure of the hydraulic pump measured by the pressure sensor reaches a threshold as a determination current value, compares the stored determination current value with a pre-stored reference current value, and determines that the performance of the hydraulic pump has deteriorated if the determination current value is greater than or equal to a set value than the reference current value, according to claim 1, the hydraulic pump performance deterioration detection system.

3. The regulator increases the capacity of the hydraulic pump as the command current increases. The hydraulic pump performance degradation detection system according to claim 2, wherein the control device increases the command current from a predetermined value when the discharge pressure of the hydraulic pump measured by the pressure sensor reaches the threshold value, and stores this current value as a determination current value.

4. The hydraulic pump performance degradation detection system according to Claim 3, wherein when the control device does not perform a performance check on the hydraulic pump, it sends a command current to the regulator such that the capacity of the hydraulic pump is maximized.

5. A hydraulic cylinder that extends and presses against the workpiece, A hydraulic pump connected to the hydraulic cylinder to form a closed circuit by a pair of supply and discharge lines, An electric motor that drives the aforementioned hydraulic pump, A control device for controlling the electric motor, The system includes a pressure sensor that measures the discharge pressure of the hydraulic pump when the hydraulic cylinder is extended, The control device adjusts the rotational speed of the electric motor so that the discharge pressure of the hydraulic pump, measured by the pressure sensor when the hydraulic cylinder is pressing the workpiece, reaches a set value, and records the adjusted rotational speed as a determination rotational speed. The system then determines whether the performance of the hydraulic pump has deteriorated by comparing the currently recorded determination rotational speed with determination rotational speeds recorded in the past.

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