Fluid-apparatus-condition monitoring device

Abstract

There is provided a fluid machine state monitoring apparatus capable of accurately diagnosing a state. A fluid machine state monitoring apparatus 102 which is used for a fluid pressure circuit 101 including a pump 2 and a pressure accumulator 5, and which is configured to diagnose a state of the pressure accumulator 5 includes: pressure detection device 6 configured for detecting a pressure of a working fluid in the fluid pressure circuit 101; and output device 10 configured for outputting a determination result at a predetermined frequency among detection results from the pressure detection device 6.

Description

{TECHNICAL FIELD}

[0001] The present invention relates to a fluid machine state monitoring apparatus, for example, a fluid machine state monitoring apparatus capable of diagnosing the state of a pressure accumulator.{BACKGROUND ART}

[0002] In various industrial fields, fluid pressure circuits in which a load is operated using a working fluid delivered from a pump are known. Such fluid pressure circuits may be provided with a pressure accumulator for preventing pulsation of the working fluid delivered from the pump or accumulating pressure.

[0003] A sealed fluid such as gas is sealed in the pressure accumulator to obtain back pressure for delivering the accumulated working fluid. The sealed fluid pressure may decrease due to leakage of the sealed fluid, damage to the pressure accumulator, deterioration over time, or the like. Since the pressure accumulator cannot discharge the working fluid when the sealed fluid pressure decreases excessively, and therefore, it is necessary to maintain the sealed fluid pressure at a certain level or higher. Therefore, a fluid machine state monitoring apparatus for monitoring the state of the pressure accumulator is known.

[0004] For example, a fluid machine state monitoring apparatus disclosed in Patent Citation 1 is mainly composed of a pressure switch and a buzzer. The pressure switch is provided in an accumulator for pulsation prevention provided between a main pump and a breaker. The pressure switch is structured such that the pressure switch detects the pressure in the accumulator and activates a relay when the detected pressure exceeds an installation pressure. The buzzer sounds upon the activation of the relay. Accordingly, the fluid machine state monitoring apparatus disclosed in Patent Citation 1 can notify an operator that the accumulator is damaged.

[0005] It is known that the peak pulsation pressure of oil flowing through a hydraulic pipe between the main pump and the breaker is larger during abnormal operation of the accumulator in which the back pressure has fallen below a minimum value than during normal operation of the accumulator in which the back pressure is normal. Therefore, the abnormal operation of the accumulator can be specified by setting the set pressure to a value higher than the peak pressure during normal operation of the accumulator.{CITATION LIST}{Patent Literature}

[0006] Patent Citation 1: JP H10-60953 A (Page 4, FIG. 1){SUMMARY OF INVENTION}{Technical Problem}

[0007] In applying the fluid machine state monitoring apparatus as described in Patent Citation 1 to an accumulator for pressure accumulation, it is necessary to change a threshold value in accordance with the pressure accumulation state of the accumulator. However, since the pressure of the working fluid changes in a waveform, it is difficult to specify the pressure accumulation state. Therefore, in the fluid machine state monitoring apparatus as described in Patent Citation 1, the state of the accumulator cannot be accurately diagnosed.

[0008] The present invention has been made in view of such problems, and an object of the present invention is to provide a fluid machine state monitoring apparatus capable of accurately diagnosing a state.{Solution to Problem}

[0009] In order to solve the foregoing problems, a fluid machine state monitoring apparatus according to the present invention is a fluid machine state monitoring apparatus which is used for a fluid pressure circuit including a pump and a pressure accumulator, and which is configured to diagnose a state of the pressure accumulator, including: a pressure detection device configured for detecting a pressure of a working fluid in the fluid pressure circuit; and an output device configured for outputting a determination result at a predetermined frequency among detection results from the pressure detection device. According to the aforesaid feature of the present invention, the state of the pressure accumulator can be accurately diagnosed by determining the pressure at the predetermined frequency.

[0010] It may be preferable that the predetermined frequency is a unique frequency determined by characteristics of the pump. According to this preferable configuration, the accuracy of the determination can be simply improved.

[0011] It may be preferable that the pressure detection device is configured to sample the pressure every 20 msec or less. According to this preferable configuration, the state of the pressure accumulator affected by the characteristics of the pump can be accurately monitored.

[0012] It may be preferable that the pressure detection devices is configured to sample the pressure every 1 to 3 msec. According to this preferable configuration, the state of the pressure accumulator affected by the characteristics of the pump can be more accurately monitored.

[0013] It may be preferable that the output device is configured to perform a determination at the predetermined frequency at a timing at which the pump and the pressure accumulator are connected. According to this preferable configuration, during discharge, since the discharge behavior differs depending on the status of a supplied circuit, it is difficult to obtain consistent behavior; however, during pressure accumulation, since the amount of delivery from the pump substantially coincides with the amount supplied to the pressure accumulator side, the behavior of the pressure accumulator is more likely to be stable, and therefore, it is easier to obtain a consistent range of behavior, and it is easier to make a determination. Accordingly, the state of the pressure accumulator can be more accurately monitored.

[0014] It may be preferable that the determination result is obtained from the pressures at the predetermined frequency detected a plurality of times. According to this preferable configuration, since the determination result is obtained from the pressures at the predetermined frequency detected a plurality of times, the accuracy of the determination result can be improved even when an irregularity such as large noise being superimposed at any of the detection timings occurs.

[0015] It may be preferable that the pressure detection device is configured to directly detect a working fluid pressure of the pressure accumulator, and the output device is configured to output, as the determination result, a result determined with respect to a predetermined reference value. According to this preferable configuration, it is possible to grasp the pressure of a sealed fluid with which the pressure accumulator is filled can be estimated from the working fluid pressure, and the degree of normality or abnormality of the value with respect to the predetermined reference value.

[0016] It may be preferable that the output device is configured to output, as the determination result, a result determined with respect to a minimum value for a safe operation. According to this preferable configuration, it is possible to grasp the degree of normality or abnormality of the pressure of the sealed fluid with which the pressure accumulator is filled, which is estimated from the working fluid pressure, with respect to the minimum value for a safe operation.{BRIEF DESCRIPTION OF DRAWINGS}

[0017] FIG. 1 is a schematic diagram illustrating a fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied. FIG. 2 is a flowchart of a diagnostic procedure performed by the fluid machine state monitoring apparatus. FIGS. 3A, 3C, and 3E are graphs illustrating changes in the pressure of a working fluid due to pulsation for each sealed gas pressure, and FIGS. 3B, 3D, and 3F are graphs illustrating absolute pressure values at a predetermined frequency for each sealed gas pressure. FIG. 4 is a schematic diagram illustrating a fluid pressure circuit to which a fluid machine state monitoring apparatus according to a second embodiment of the present invention is applied. FIGS. 5A, 5B, and 5C are graphs illustrating changes in gas pressure due to pulsation for each sealed gas pressure. {DESCRIPTION OF EMBODIMENTS}

[0018] Modes for implementing a fluid machine state monitoring apparatus according to the present invention will be described below based on embodiments.{First embodiment}

[0019] A fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied will be described with reference to FIGS. 1 to 3. In the following description, the right and left sides when viewed from the front of FIG. 1 correspond to the right and left sides of the valve position of an electromagnetic direction switching valve.

[0020] A hydraulic circuit serving as the fluid pressure circuit according to the first embodiment delivers oil serving as a working fluid to a supply destination in response to a command in work machines, construction machines, cargo handling vehicles, automobiles, electric trains, wind power generation systems, or the like.

[0021] As illustrated in FIG. 1, a hydraulic circuit 101 is mainly composed of a drive mechanism 1, a hydraulic pump 2, an electromagnetic direction switching valve 3 (hereinafter, referred to as the direction switching valve 3), a check valve 4, an accumulator 5, a pressure sensor 6, an electromagnetic switching valve 7, a hydraulic pressure supplied circuit 8 serving as a supply destination, a tank 9, a control device 10, a monitor 11, and a relief valve 12.

[0022] The hydraulic pump 2 is coupled to the drive mechanism 1 such as an internal combustion engine, and is rotated by power from the drive mechanism 1, thereby supplying the oil serving as a working fluid to a downstream side. The oil delivered from the hydraulic pump 2 passes through a pipeline 18, and flows into the direction switching valve 3. Incidentally, the hydraulic pump 2 of the present embodiment is of a variable capacity type, but may be of a fixed capacity type.

[0023] The direction switching valve 3 is a spring-centered type three-position, four-port electromagnetic switching valve. The direction switching valve 3 in a neutral position 3-1 connects the pipeline 18 to a pipeline 19. The pipeline 19 is connected to the tank 9. Therefore, the entire amount of oil delivered from the hydraulic pump 2 is discharged to the tank 9.

[0024] The direction switching valve 3 includes solenoids 3a and 3b. The solenoids 3a and 3b are electrically connected to the control device 10 through electrical signal lines 13 and 14.

[0025] The control device 10 outputs an electrical signal to the electrical signal line 13 when the pressure value detected by the pressure sensor 6 to be described later becomes less than or equal to a predetermined value in a state in which an operation command for operating a load provided in the hydraulic pressure supplied circuit 8 is not input.

[0026] In the direction switching valve 3, when the solenoid 3a is energized by an electrical signal applied through the electrical signal line 13, a spool moves in a left direction and switches to a right position 3-2. The direction switching valve 3 in the right position 3-2 connects the pipeline 18 to a pipeline 20, and shuts off the pipeline 19 from a pipeline 21. Incidentally, a return flow passage from the hydraulic pressure supplied circuit 8 to the tank 9 is provided inside the hydraulic pressure supplied circuit 8.

[0027] The pipeline 20 is connected to the check valve 4. The check valve 4 is connected to the accumulator 5 through a pipeline 22. The check valve 4 is configured to allow the oil to pass therethrough from the pipeline 20 to the pipeline 22. Accordingly, the oil delivered from the hydraulic pump 2 is accumulated under pressure in the accumulator 5.

[0028] In addition, the pipeline 18 is branched and communicably connected to a pipeline 23 with the relief valve 12 interposed therebetween. The pipeline 23 is connected to the tank 9. Accordingly, when the pressure in the pipeline 18 rises to a predetermined level or higher, the relief valve 12 is opened to discharge the oil to the tank 9, so that the circuit can be protected.

[0029] The accumulator 5 is mainly composed of a pressure-resistant shell and a balloon-shaped bladder. The shell is connected to the pipeline 22 to the oil to flow in and out. The bladder is disposed inside the shell. In the present embodiment, a sealed fluid sealed in the bladder is nitrogen gas; however, the sealed fluid may be other gases such as air, and may be changed as appropriate. In addition, in the following description, the sealed fluid is simply referred to as "gas". Here, the pressure in the bladder is the back pressure of the accumulator 5.

[0030] In the accumulator 5, as the hydraulic pressure in the shell increases, the bladder contracts and the oil in the pipeline 22 flows into the shell. In addition, in the accumulator 5, as the hydraulic pressure in the shell decreases in a state in which the bladder is contracted, the contraction of the bladder is released and the oil in the shell is discharged into the pipeline 22.

[0031] In addition, the filling or discharge of the gas from the bladder can be performed through a valve (not illustrated). Incidentally, the accumulator is not limited to a bladder type as in the present embodiment, and may be of a piston type or may be changed as appropriate.

[0032] The pipeline 22 is further branched in two directions, and is also connected to the pressure sensor 6 and the electromagnetic switching valve 7.

[0033] The pressure sensor 6 is electrically connected to the control device 10 through an electrical signal line 15. The pressure sensor 6 detects the pressure in the pipeline 22, and outputs a pressure signal capable of specifying the pressure to the electrical signal line 15. The pressure in the pipeline 22 is substantially the same as the pressure of the oil accumulated under pressure in the accumulator 5.

[0034] The electromagnetic switching valve 7 is a spring-offset type two-position, two-port electromagnetic switching valve. The electromagnetic switching valve 7 in an offset position 7-1 prevents communication between the pipeline 21 and the pipeline 22.

[0035] In addition, the solenoid of the electromagnetic switching valve 7 is electrically connected to the control device 10 through an electrical signal line 16. In the electromagnetic switching valve 7, when the solenoid is energized by an electrical signal applied through the electrical signal line 16, a spool moves and switches to an onset position 7-2.

[0036] The electromagnetic switching valve 7 in the onset position 7-2 connects the pipelines 21 and 22 to allow the oil to pass from the pipeline 22 side to the pipeline 21. Accordingly, the oil discharged from the accumulator 5 can be supplied to the hydraulic pressure supplied circuit 8. At this time, the control device 10 sets the direction switching valve 3 to the neutral position 3-1.

[0037] In addition, when an operation command is input, the control device 10 outputs an electrical signal to the electrical signal line 14.

[0038] In the direction switching valve 3, when the solenoid 3b is energized by an electrical signal applied through the electrical signal line 14, a spool moves in a right direction and switches to a left position 3-3. The direction switching valve 3 in the left position 3-3 connects the pipeline 18 to the pipeline 21, and connects the pipeline 19 to the pipeline 20.

[0039] The pipeline 21 is branched in two directions, and is connected to the electromagnetic switching valve 7 and the hydraulic pressure supplied circuit 8. Accordingly, the oil delivered from the hydraulic pump 2 flows into the hydraulic pressure supplied circuit 8.

[0040] The hydraulic pressure supplied circuit 8 is a circuit in which a load is provided. Incidentally, the load may be an actuator such as a hydraulic cylinder or a hydraulic motor, or may be a pressure increasing device, a power generation device, or the like, and may be changed as appropriate.

[0041] Next, a fluid machine state monitoring apparatus 102 of the present embodiment will be described. The fluid machine state monitoring apparatus 102 is mainly composed of the pressure sensor 6 serving as a pressure detection device, the control device 10 serving as an output device, and the monitor 11 serving as a notification device.

[0042] The control device 10 estimates the sealed gas pressure in the accumulator 5 based on the pressure value inside the accumulator 5 input from the pressure sensor 6, and outputs, as the determination result, the ratio of the estimated sealed gas pressure to an appropriate sealed gas pressure, such as the sealed gas pressure when fully filled, that is, at the time of factory shipment, or when refilled with the sealed gas, to the monitor 11 through an electrical signal line 17. Hereinafter, a diagnostic procedure for the accumulator 5 by the fluid machine state monitoring apparatus 102 will be described with reference to FIGS. 2 and 3.

[0043] Incidentally, the sealed gas pressure in this specification refers to gas pressure in a state in which no oil flows into the accumulator 5. On the other hand, the sealed gas pressure may be the pressure in a state in which the accumulator 5 is fully filled with the oil, and may be changed as appropriate as long as the sealed gas pressure is a reference gas pressure detected under the same conditions.

[0044] As illustrated in FIG. 2, the control device 10 repeatedly executes step S1 until the control device 10 outputs an electrical signal to the electrical signal line 13 (step S1: N). When the pressure detected by the pressure sensor 6 increases to a certain level or higher, it is determined that pressure accumulation is in progress (step S1: Y), and the process proceeds to step S2.

[0045] Incidentally, regarding the method for determining whether pressure accumulation is in progress, the control device 10 may determine that pressure accumulation is in progress by outputting an electrical signal to the electrical signal line 13, or the method may be changed as appropriate.

[0046] When the process proceeds to step S2, the control device 10 receives pressure values sampled every 2 msec by the pressure sensor 6, and derives absolute pressure values at a predetermined frequency by performing a fast Fourier transform (hereinafter, referred to as "FFT') on waveforms obtained from the pressure values.

[0047] Incidentally, the waveforms illustrated in FIGS. 3A, 3C, and 3E that are formed by detection values sampled every 2 msec by the pressure sensor 6 are detection results by the pressure detection device of the present invention, and in more detail, the waveform in the period from 0.00 sec, which is the start time of step S2, to 0.10 sec is regarded as one detection result. The control device 10 performs an FFT on the one detection result. The same applies to step S4 to be described later.

[0048] For details regarding steps S2 and S4, referring to FIGS. 3A, 3C, and 3E, it can be seen that the pressure value input from the pressure sensor 6 to the control device 10 during pressure accumulation changes in a waveform over time. In addition, it can be confirmed that there is a regularity in which a plurality of consecutive cycles with large amplitude are followed by one cycle with small amplitude. That is, it can be seen that the oil delivered from the hydraulic pump 2 pulsates.

[0049] It has been found that the pulsation of the oil delivered from the hydraulic pump 2 has a frequency inherent to the pump. When the frequency of the hydraulic pump 2 is measured in a state in which the hydraulic circuit 101 is configured, a predetermined frequency to be measured can be specified. Specifically, in experiments to be described later, when the hydraulic pump 2 having a pulsation of 225 Hz was used, the predetermined frequency was approximately 223.1 Hz (see FIGS. 3B, 3D, and 3F).

[0050] It has been found through experiments that the absolute pressure value at the predetermined frequency and the sealed gas pressure show a correlation such that the absolute pressure value at the predetermined frequency increases as the sealed gas pressure decrease. FIG. 3 collectively illustrates one example of the experimental results.

[0051] Incidentally, FIGS. 3A, 3C, and 3E illustrate changes in pressure detected by the pressure sensor 6 in order to clearly illustrate increases and decreases in pressure, and the units or scales of pressure are the same. That is, the units or scales of pressure on the vertical axis are matched and displayed.

[0052] FIG. 3A illustrates the waveform of pressure values obtained as a detection result by the pressure sensor 6 when the hydraulic pump 2 is operated with the sealed gas pressure set to 2.0 MPa. FIG. 3B illustrates the absolute pressure value, that is, the amplitude extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3A. The absolute pressure value at the predetermined frequency was approximately 0.015 MPa.

[0053] FIG. 3C illustrates the waveform of pressure values obtained as a detection result when the sealed gas pressure is set to 1.8 MPa. FIG. 3D illustrates the absolute pressure value extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3C. The absolute pressure value at the predetermined frequency was approximately 0.019 MPa.

[0054] FIG. 3E illustrates the waveform of pressure values obtained as a detection result when the sealed gas pressure is set to 1.6 MPa. FIG. 3F illustrates the absolute pressure value extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3E. The absolute pressure value at the predetermined frequency was approximately 0.022 MPa.

[0055] From above description, the correlation between the absolute pressure value at the predetermined frequency and the sealed gas pressure in the bladder is clear. Therefore, the absolute pressure value at the predetermined frequency obtained in a state in which the bladder is fully filled with gas is used as a set value, and the set value is compared with the absolute pressure value at the predetermined frequency obtained in step S2 (step S3).

[0056] If the absolute pressure value at the predetermined frequency obtained in step S2 is less than or equal to the set value, it is determined that the bladder is fully filled with gas (step S3: N). Next, the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display 100%.

[0057] Incidentally, here, 100% refers the ratio when the sealed gas pressure when fully filled is equal to the estimated sealed gas pressure. In addition, the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled is defined as 0% when the estimated sealed gas pressure is equal to atmospheric pressure. The sealed gas pressure when fully filled is a predetermined reference value in the present invention.

[0058] In addition, regarding the comparison between the absolute pressure value at the predetermined frequency and the set value, it may be determined whether the absolute pressure value at the predetermined frequency is included within a certain range including the set value, for example, within a range of ± 5% of the set value, or may be changed as appropriate.

[0059] Thereafter, the control device 10 ends the diagnosis of the accumulator 5. After the diagnosis is ended, if pressure accumulation is in progress (step S1: Y), steps S2 and S3 are newly executed.

[0060] Meanwhile, if the absolute pressure value at the predetermined frequency obtained in step S2 is larger than the set value, it can be estimated that an abnormality such as gas leakage or deterioration of the bladder has occurred (step S3: Y). In this case, pressure values newly sampled every 2 msec by the pressure sensor 6 are input, and an FFT is performed on a waveform obtained from the pressure values to specify an absolute pressure value at the predetermined frequency (step S4).

[0061] In step S5, the control device 10 compares the set value and the absolute pressure value at the predetermined frequency obtained in step S4. If the absolute pressure value at the predetermined frequency obtained in step S4 is less than or equal to the set value (step S5: N), the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display 100%. Thereafter, the diagnosis of the accumulator 5 is ended.

[0062] If the absolute pressure value at the predetermined frequency obtained in step S4 is larger than the set value (step S5: Y), the control device 10 proceeds to step S6.

[0063] In step S6, the control device 10 looks up the absolute pressure value at the predetermined frequency obtained in step S2 in a table (not illustrated), and specifies a corresponding pressure value set in advance based on experimental results or the like. Similarly, the absolute pressure value at the predetermined frequency obtained in step S4 is looked up in the same table to specify the corresponding pressure value. Then, an average value is calculated from each pressure value specified from the absolute pressure value at the predetermined frequency in each of steps S2 and S4. The average value is specified as the estimated sealed gas pressure.

[0064] Incidentally, the present invention is not limited to a configuration in which the absolute pressure value at the predetermined frequency is looked up in the table to specify the corresponding pressure value, and a configuration in which the corresponding pressure value is calculated by substituting the absolute pressure value at the predetermined frequency into an equation may be employed, and the method for specifying the estimated sealed gas pressure may be changed as appropriate.

[0065] In step S7, the control device 10 calculates the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled.

[0066] Thereafter, the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled, for example, 70%. Accordingly, it is possible to grasp the extent to which the estimated sealed gas pressure is located relative to the sealed gas pressure when fully filled, that is, the degree of normality or abnormality.

[0067] In addition, in step S8, the control device 10 also outputs an electrical signal to the monitor 11 to display the ratio of the minimum value of the sealed gas pressure, at which the accumulator 5 is safely operable, to the sealed gas pressure when fully filled, for example, 60%. Accordingly, it is possible to grasp the extent to which the sealed gas pressure estimated from the waveform of hydraulic pressure is located relative to the minimum value at which the accumulator 5 is safely operable, that is, the degree of normality or abnormality.

[0068] Incidentally, the ratio of the minimum value, at which the accumulator 5 is safely operable, to the sealed gas pressure when fully filled may also be displayed on the monitor 11 when the conditions in step S3 or step S5 are not satisfied (S3, S5: N).

[0069] Furthermore, if the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled is 100%, the monitor 11 or a light-emitting device (not illustrated) such as a light bulb may be caused to emit blue light, if the ratio falls below 90%, the monitor 11 or the light-emitting device may be caused to emit yellow light, and if the ratio falls below 70%, the monitor 11 or the light-emitting device may be caused to emit red light.

[0070] In addition, an alarm corresponding to the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled may be sounded, or an alarm may be sounded for a period of time corresponding to the ratio. That is, the notification mode may be changed as appropriate as long as it is possible to grasp the extent to which the estimated sealed gas pressure is located relative to the minimum value at which the accumulator 5 is safely operable.

[0071] As described above, the fluid machine state monitoring apparatus 102 of the present embodiment can accurately diagnose the state of the accumulator 5 by determining the absolute pressure value at the predetermined frequency.

[0072] In addition, the absolute pressure value at the predetermined frequency changes in accordance with the sealed gas pressure, whereas the absolute pressure value at the predetermined frequency is hardly affected by the pressure accumulation state of the accumulator 5. Therefore, whether the accumulator is the accumulator 5 for pressure accumulation as in the present embodiment or the accumulator for pulsation prevention as in Patent Citation 1, the state of the accumulator can be accurately diagnosed.

[0073] In addition, the absolute pressure value at the predetermined frequency changes in accordance with the sealed gas pressure, whereas the absolute pressure value at the predetermined frequency is hardly affected by the amount of delivery per unit time from the hydraulic pump 2. Therefore, even when the amount of delivery per unit time is changed, that is, even when the pump is changed, the absolute pressure value at the predetermined frequency is not affected, and for example, even when the pump is replaced with a pump with different delivery performance, the state of the accumulator 5 can be accurately diagnosed.

[0074] In addition, since the predetermined frequency of the present embodiment is a natural frequency based on the characteristics of the hydraulic pump 2, the accuracy of the determination can be simply improved.

[0075] In addition, since the pressure sensor 6 samples pressure values every 2 msec less than or equal to 20 msec, the state of the accumulator 5 that is affected by the characteristics of the hydraulic pump 2 can be more accurately monitored.

[0076] Incidentally, the pressure sensor 6 preferably samples pressure values every 20 msec or less, and more preferably every 1 to 3 msec. The reason is that the shorter the sampling interval is, the easier it becomes to specify absolute pressure values at higher frequencies using FFT.

[0077] In addition, the fluid machine state monitoring apparatus 102 determines the maximum pressure value at the predetermined frequency at the timing at which the hydraulic pump 2 and the accumulator 5 are connected in the circuit. During pressure accumulation when the amount of delivery from the hydraulic pump 2 substantially coincides with the amount supplied to the accumulator 5 side, the behavior of the accumulator 5 is more likely to be stable, thereby allowing consistent behavior with less noise to be obtained, and enabling easier determination, compared to during discharge when the accumulator 5 is affected by the operating status on the hydraulic pressure supplied circuit 8 side, thereby making it difficult to obtain consistent behavior, and resulting in unstable behavior, such as intermittent operation. Accordingly, the state of the accumulator 5 can be more accurately monitored.

[0078] In addition, in the present embodiment, in diagnosing the accumulator 5, the absolute pressure value at the predetermined frequency is determined in steps S2 and S3, and the absolute pressure value at the predetermined frequency is further determined in steps S4 and S5. For example, even when an irregularity such as an impact occurs in steps S2 and S3 and the process proceeds to step S4, the absolute pressure value at the predetermined frequency in a state in which no irregularity is included can be obtained and determined in steps S4 and S5. Accordingly, the accuracy of the determination result can be improved.

[0079] In addition, since the average value of the pressure value corresponding to the absolute pressure value at the predetermined frequency specified in step S2 and the pressure value corresponding to the absolute pressure value at the predetermined frequency specified in step S4 is specified as the estimated sealed gas pressure, it is easier to reduce the error between the estimated sealed gas pressure and the actual sealed gas pressure compared to a configuration in which only one of the pressure values is adopted.

[0080] Incidentally, in the present embodiment, the output device has been described as being configured to make an operator recognize the determination result through display, sound, or the like; however, the present invention is not limited thereto. For example, a configuration in which the determination result is to restrict the direction switching valve 3 from switching to the right position 3-2 may be employed, and the method may be changed as appropriate.{Second embodiment}

[0081] Next, a fluid machine state monitoring apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. Incidentally, the description of configurations that are the same as and overlap with the configurations of the first embodiment will be omitted.

[0082] As illustrated in FIG. 4, a fluid machine state monitoring apparatus 202 provided in a hydraulic circuit 201 of the second embodiment is mainly composed of a pressure sensor 106 serving as the pressure detection device, the control device 10, and the monitor 11.

[0083] The pressure sensor 106 is connected to the accumulator 5. In addition, the pressure sensor 106 is electrically connected to the control device 10 through an electrical signal line 115. The pressure sensor 106 detects the gas pressure in the bladder, and outputs a pressure signal capable of specifying the gas pressure to the electrical signal line 115.

[0084] As illustrated in FIG. 5, it can be seen that the pressure value input from the pressure sensor 106 to the control device 10 during pressure accumulation changes in a waveform over time. That is, it can be seen that the gas sealed in the bladder is affected by the pulsation of the oil delivered from the hydraulic pump 2. In more detail, it can be seen that the gas pressure also changes in the same manner as the hydraulic pressure in the accumulator 5 changes. That is, the pressure sensor 106 can detect changes in hydraulic pressure from changes in gas pressure.

[0085] Accordingly, similarly to the first embodiment, the control device 10 can derive an absolute pressure value at a predetermined frequency by performing an FFT on a waveform obtained from a plurality of pressure values input from the pressure sensor 106.

[0086] Incidentally, the absolute pressure value at the predetermined frequency derived by performing an FFT on the waveform obtained from the pressure values detected by the pressure sensor 106 as in the present embodiment and the absolute pressure value at the predetermined frequency derived by performing an FFT on the waveform obtained from the pressure values detected by the pressure sensor 6 as in the first embodiment may be used in combination. That is, two pressure sensors 6 and 106 may be used in combination as the pressure detection device.

[0087] The embodiments of the present invention have been described above with reference to the drawings; however, the specific configurations are not limited to these embodiments, and modifications or additions that are made without departing from the scope of the present invention are also included in the present invention.

[0088] For example, in the first and second embodiments, the fluid pressure circuit has been described as a hydraulic circuit in which oil is pumped; however, the present invention is not limited thereto. The working fluid may be a fluid other than oil, and the fluid to be applied may be changed as appropriate.

[0089] In addition, in the first and second embodiments, a configuration in which the working fluid delivered from the pump is directly supplied to the pressure accumulator has been described; however, the present invention is not limited thereto, and a configuration in which an actuator is provided between the pump and the pressure accumulator and the working fluid delivered from the actuator is supplied to the pressure accumulator may be employed. Even with such a configuration, the state of the pressure accumulator can be diagnosed by specifying a predetermined frequency in the fluid pressure circuit and obtaining a pressure at the frequency.

[0090] In addition, in the first and second embodiments, an example of the type of pressure accumulator that accumulates the working fluid, which is delivered from the pump, under pressure in order to discharge the working fluid when needed has been provided; however, the present invention is not limited thereto, and the pressure accumulator may be used for pulsation prevention or may be used for energy regeneration. In addition, the pressure accumulator in the present invention may be any device capable of temporarily storing and discharging the working fluid, such as an air chamber or a damper, and may be changed as appropriate.

[0091] In addition, in the first and second embodiments, a configuration in which the state of the pressure accumulator is diagnosed based on the pulsation during pressure accumulation has been described; however, the present invention is not limited thereto, and the diagnosis may be performed based on the pulsation during discharge or the pulsation in a constant-pressure state.

[0092] In addition, in the first and second embodiments, the determination result has been described as the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled; however, the present invention is not limited thereto. The determination result may be the absolute pressure value at the predetermined frequency, may be the estimated sealed gas pressure itself, may be the amount of sealed gas corresponding to the estimated sealed gas pressure, or may be the ratio of the estimated amount of sealed gas to the amount of sealed gas when fully filled, the ratio of the estimated sealed gas pressure to the minimum value for safe operation may be output as the determination result, or the determination result may simply be whether the sealed gas pressure has decreased, and the type of determination result may be changed as appropriate.

[0093] In addition, in the first and second embodiments, a configuration in which when it is determined that the absolute pressure value at the predetermined frequency is larger than the set value in two consecutive instances, it is diagnosed that an abnormality has occurred in the pressure accumulator has been described; however, the present invention is not limited thereto. When it is determined that the absolute pressure value at the predetermined frequency is larger than the set value in three or more consecutive instances, it may be diagnosed that an abnormality has occurred in the pressure accumulator, or when it is determined once that the absolute pressure value at the predetermined frequency is larger than the set value, it may be diagnosed that an abnormality has occurred in the pressure accumulator, and the determination criteria may be changed as appropriate.

[0094] In addition, in the first and second embodiments, a configuration in which an average value is calculated from each pressure value specified from the absolute pressure values at the predetermined frequency detected two times has been described; however, the present invention is not limited thereto. A pressure value that are considered to strongly reflect irregularities may be excluded from the plurality of specified pressure values using a filter, or any value other than the average value may be used as long as the influence of irregularities can be reduced.

[0095] In addition, in the first and second embodiments, the pressure detection device has been described as being configured as a pressure sensor; however, the present invention is not limited thereto, and the pressure detection device may be composed of a pressure sensor and a control device. That is, a configuration in which the control device samples pressure data, which is sequentially input to the control device from the pressure sensor, at predetermined time intervals to obtain a pressure value may be employed.

[0096] In addition, in the first and second embodiments, one detection result has been described as a plurality of pressure values constituting a waveform from 0.00 sec to 0.10 sec; however, the present invention is not limited thereto. As long as the pressure at the predetermined frequency can be specified, one detection result may be one pressure value, may be a plurality of pressure values corresponding to one cycle, may be a plurality of pressure values corresponding to a predetermined plurality of cycles, may be a plurality of pressure values obtained per another unit time, or the detection result may be changed as appropriate. In addition, from the viewpoint of being able to reduce the influence of irregularities, a larger number of cycles is preferable.

[0097] In addition, in the first and second embodiments, the control device serving as the output device has been described as being configured to also control the direction switching valve, the electromagnetic switching valve, and the like; however, the present invention is not limited thereto. The control device may be provided separately from a control device that controls the direction switching valve, the electromagnetic switching valve, and the like, and may be, for example, a cloud server or the like. If the output device is configured as a cloud server, the pressure detection device or the notification device may be wirelessly connected to the cloud server. In other words, the pressure detection device or the notification device may include a communication device.

[0098] Further, the notification device may be a smartphone or a tablet terminal. With such a configuration, the determination result may be transmitted from the cloud server as a notification or email, or a user may access the cloud server and receive the determination result, and the notification method may be changed as appropriate. In addition, if the pressure detection device includes a wireless communication device, a microcontroller, which is an output device, or the like, the determination result may be output to the cloud server.

[0099] In addition, in the first and second embodiments, tests were performed at room temperature; however, in consideration of climate or temperature changes to which the internal fluid is subjected, values obtained by applying temperature correction to the test results may be used.{REFERENCE SIGNS LIST}

[0100] 2Hydraulic pump (pump) 5Accumulator (pressure accumulator) 6Pressure sensor (pressure detection device) 8Hydraulic pressure supplied circuit (supply destination) 10Control device (output device) 11Monitor (notification device) 101Hydraulic circuit (fluid pressure circuit) 102fluid machine state monitoring apparatus 106Pressure sensor (pressure detection device) 201Hydraulic circuit (fluid pressure circuit) 202fluid machine state monitoring apparatus

Examples

first embodiment

{First embodiment}

[0019]A fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied will be described with reference to FIGS. 1 to 3. In the following description, the right and left sides when viewed from the front of FIG. 1 correspond to the right and left sides of the valve position of an electromagnetic direction switching valve.

[0020]A hydraulic circuit serving as the fluid pressure circuit according to the first embodiment delivers oil serving as a working fluid to a supply destination in response to a command in work machines, construction machines, cargo handling vehicles, automobiles, electric trains, wind power generation systems, or the like.

[0021]As illustrated in FIG. 1, a hydraulic circuit 101 is mainly composed of a drive mechanism 1, a hydraulic pump 2, an electromagnetic direction switching valve 3 (hereinafter, referred to as the direction switching valve 3), a check valve 4, an ac...

second embodiment

{Second embodiment}

[0081]Next, a fluid machine state monitoring apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. Incidentally, the description of configurations that are the same as and overlap with the configurations of the first embodiment will be omitted.

[0082]As illustrated in FIG. 4, a fluid machine state monitoring apparatus 202 provided in a hydraulic circuit 201 of the second embodiment is mainly composed of a pressure sensor 106 serving as the pressure detection device, the control device 10, and the monitor 11.

[0083]The pressure sensor 106 is connected to the accumulator 5. In addition, the pressure sensor 106 is electrically connected to the control device 10 through an electrical signal line 115. The pressure sensor 106 detects the gas pressure in the bladder, and outputs a pressure signal capable of specifying the gas pressure to the electrical signal line 115.

[0084] As illustrated in FIG. 5, it can b...

{TECHNICAL FIELD}

[0001] The present invention relates to a fluid machine state monitoring apparatus, for example, a fluid machine state monitoring apparatus capable of diagnosing the state of a pressure accumulator.{BACKGROUND ART}

[0002] In various industrial fields, fluid pressure circuits in which a load is operated using a working fluid delivered from a pump are known. Such fluid pressure circuits may be provided with a pressure accumulator for preventing pulsation of the working fluid delivered from the pump or accumulating pressure.

[0003] A sealed fluid such as gas is sealed in the pressure accumulator to obtain back pressure for delivering the accumulated working fluid. The sealed fluid pressure may decrease due to leakage of the sealed fluid, damage to the pressure accumulator, deterioration over time, or the like. Since the pressure accumulator cannot discharge the working fluid when the sealed fluid pressure decreases excessively, and therefore, it is necessary to maintain the sealed fluid pressure at a certain level or higher. Therefore, a fluid machine state monitoring apparatus for monitoring the state of the pressure accumulator is known.

[0004] For example, a fluid machine state monitoring apparatus disclosed in Patent Citation 1 is mainly composed of a pressure switch and a buzzer. The pressure switch is provided in an accumulator for pulsation prevention provided between a main pump and a breaker. The pressure switch is structured such that the pressure switch detects the pressure in the accumulator and activates a relay when the detected pressure exceeds an installation pressure. The buzzer sounds upon the activation of the relay. Accordingly, the fluid machine state monitoring apparatus disclosed in Patent Citation 1 can notify an operator that the accumulator is damaged.

[0005] It is known that the peak pulsation pressure of oil flowing through a hydraulic pipe between the main pump and the breaker is larger during abnormal operation of the accumulator in which the back pressure has fallen below a minimum value than during normal operation of the accumulator in which the back pressure is normal. Therefore, the abnormal operation of the accumulator can be specified by setting the set pressure to a value higher than the peak pressure during normal operation of the accumulator.{CITATION LIST}{Patent Literature}

[0006] Patent Citation 1: JP H10-60953 A (Page 4, FIG. 1){SUMMARY OF INVENTION}{Technical Problem}

[0007] In applying the fluid machine state monitoring apparatus as described in Patent Citation 1 to an accumulator for pressure accumulation, it is necessary to change a threshold value in accordance with the pressure accumulation state of the accumulator. However, since the pressure of the working fluid changes in a waveform, it is difficult to specify the pressure accumulation state. Therefore, in the fluid machine state monitoring apparatus as described in Patent Citation 1, the state of the accumulator cannot be accurately diagnosed.

[0008] The present invention has been made in view of such problems, and an object of the present invention is to provide a fluid machine state monitoring apparatus capable of accurately diagnosing a state.{Solution to Problem}

[0009] In order to solve the foregoing problems, a fluid machine state monitoring apparatus according to the present invention is a fluid machine state monitoring apparatus which is used for a fluid pressure circuit including a pump and a pressure accumulator, and which is configured to diagnose a state of the pressure accumulator, including: a pressure detection device configured for detecting a pressure of a working fluid in the fluid pressure circuit; and an output device configured for outputting a determination result at a predetermined frequency among detection results from the pressure detection device. According to the aforesaid feature of the present invention, the state of the pressure accumulator can be accurately diagnosed by determining the pressure at the predetermined frequency.

[0010] It may be preferable that the predetermined frequency is a unique frequency determined by characteristics of the pump. According to this preferable configuration, the accuracy of the determination can be simply improved.

[0011] It may be preferable that the pressure detection device is configured to sample the pressure every 20 msec or less. According to this preferable configuration, the state of the pressure accumulator affected by the characteristics of the pump can be accurately monitored.

[0012] It may be preferable that the pressure detection devices is configured to sample the pressure every 1 to 3 msec. According to this preferable configuration, the state of the pressure accumulator affected by the characteristics of the pump can be more accurately monitored.

[0013] It may be preferable that the output device is configured to perform a determination at the predetermined frequency at a timing at which the pump and the pressure accumulator are connected. According to this preferable configuration, during discharge, since the discharge behavior differs depending on the status of a supplied circuit, it is difficult to obtain consistent behavior; however, during pressure accumulation, since the amount of delivery from the pump substantially coincides with the amount supplied to the pressure accumulator side, the behavior of the pressure accumulator is more likely to be stable, and therefore, it is easier to obtain a consistent range of behavior, and it is easier to make a determination. Accordingly, the state of the pressure accumulator can be more accurately monitored.

[0014] It may be preferable that the determination result is obtained from the pressures at the predetermined frequency detected a plurality of times. According to this preferable configuration, since the determination result is obtained from the pressures at the predetermined frequency detected a plurality of times, the accuracy of the determination result can be improved even when an irregularity such as large noise being superimposed at any of the detection timings occurs.

[0015] It may be preferable that the pressure detection device is configured to directly detect a working fluid pressure of the pressure accumulator, and the output device is configured to output, as the determination result, a result determined with respect to a predetermined reference value. According to this preferable configuration, it is possible to grasp the pressure of a sealed fluid with which the pressure accumulator is filled can be estimated from the working fluid pressure, and the degree of normality or abnormality of the value with respect to the predetermined reference value.

[0016] It may be preferable that the output device is configured to output, as the determination result, a result determined with respect to a minimum value for a safe operation. According to this preferable configuration, it is possible to grasp the degree of normality or abnormality of the pressure of the sealed fluid with which the pressure accumulator is filled, which is estimated from the working fluid pressure, with respect to the minimum value for a safe operation.{BRIEF DESCRIPTION OF DRAWINGS}

[0017] FIG. 1 is a schematic diagram illustrating a fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied. FIG. 2 is a flowchart of a diagnostic procedure performed by the fluid machine state monitoring apparatus. FIGS. 3A, 3C, and 3E are graphs illustrating changes in the pressure of a working fluid due to pulsation for each sealed gas pressure, and FIGS. 3B, 3D, and 3F are graphs illustrating absolute pressure values at a predetermined frequency for each sealed gas pressure. FIG. 4 is a schematic diagram illustrating a fluid pressure circuit to which a fluid machine state monitoring apparatus according to a second embodiment of the present invention is applied. FIGS. 5A, 5B, and 5C are graphs illustrating changes in gas pressure due to pulsation for each sealed gas pressure. {DESCRIPTION OF EMBODIMENTS}

[0018] Modes for implementing a fluid machine state monitoring apparatus according to the present invention will be described below based on embodiments.{First embodiment}

[0019] A fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied will be described with reference to FIGS. 1 to 3. In the following description, the right and left sides when viewed from the front of FIG. 1 correspond to the right and left sides of the valve position of an electromagnetic direction switching valve.

[0020] A hydraulic circuit serving as the fluid pressure circuit according to the first embodiment delivers oil serving as a working fluid to a supply destination in response to a command in work machines, construction machines, cargo handling vehicles, automobiles, electric trains, wind power generation systems, or the like.

[0021] As illustrated in FIG. 1, a hydraulic circuit 101 is mainly composed of a drive mechanism 1, a hydraulic pump 2, an electromagnetic direction switching valve 3 (hereinafter, referred to as the direction switching valve 3), a check valve 4, an accumulator 5, a pressure sensor 6, an electromagnetic switching valve 7, a hydraulic pressure supplied circuit 8 serving as a supply destination, a tank 9, a control device 10, a monitor 11, and a relief valve 12.

[0022] The hydraulic pump 2 is coupled to the drive mechanism 1 such as an internal combustion engine, and is rotated by power from the drive mechanism 1, thereby supplying the oil serving as a working fluid to a downstream side. The oil delivered from the hydraulic pump 2 passes through a pipeline 18, and flows into the direction switching valve 3. Incidentally, the hydraulic pump 2 of the present embodiment is of a variable capacity type, but may be of a fixed capacity type.

[0023] The direction switching valve 3 is a spring-centered type three-position, four-port electromagnetic switching valve. The direction switching valve 3 in a neutral position 3-1 connects the pipeline 18 to a pipeline 19. The pipeline 19 is connected to the tank 9. Therefore, the entire amount of oil delivered from the hydraulic pump 2 is discharged to the tank 9.

[0024] The direction switching valve 3 includes solenoids 3a and 3b. The solenoids 3a and 3b are electrically connected to the control device 10 through electrical signal lines 13 and 14.

[0025] The control device 10 outputs an electrical signal to the electrical signal line 13 when the pressure value detected by the pressure sensor 6 to be described later becomes less than or equal to a predetermined value in a state in which an operation command for operating a load provided in the hydraulic pressure supplied circuit 8 is not input.

[0026] In the direction switching valve 3, when the solenoid 3a is energized by an electrical signal applied through the electrical signal line 13, a spool moves in a left direction and switches to a right position 3-2. The direction switching valve 3 in the right position 3-2 connects the pipeline 18 to a pipeline 20, and shuts off the pipeline 19 from a pipeline 21. Incidentally, a return flow passage from the hydraulic pressure supplied circuit 8 to the tank 9 is provided inside the hydraulic pressure supplied circuit 8.

[0027] The pipeline 20 is connected to the check valve 4. The check valve 4 is connected to the accumulator 5 through a pipeline 22. The check valve 4 is configured to allow the oil to pass therethrough from the pipeline 20 to the pipeline 22. Accordingly, the oil delivered from the hydraulic pump 2 is accumulated under pressure in the accumulator 5.

[0028] In addition, the pipeline 18 is branched and communicably connected to a pipeline 23 with the relief valve 12 interposed therebetween. The pipeline 23 is connected to the tank 9. Accordingly, when the pressure in the pipeline 18 rises to a predetermined level or higher, the relief valve 12 is opened to discharge the oil to the tank 9, so that the circuit can be protected.

[0029] The accumulator 5 is mainly composed of a pressure-resistant shell and a balloon-shaped bladder. The shell is connected to the pipeline 22 to the oil to flow in and out. The bladder is disposed inside the shell. In the present embodiment, a sealed fluid sealed in the bladder is nitrogen gas; however, the sealed fluid may be other gases such as air, and may be changed as appropriate. In addition, in the following description, the sealed fluid is simply referred to as "gas". Here, the pressure in the bladder is the back pressure of the accumulator 5.

[0030] In the accumulator 5, as the hydraulic pressure in the shell increases, the bladder contracts and the oil in the pipeline 22 flows into the shell. In addition, in the accumulator 5, as the hydraulic pressure in the shell decreases in a state in which the bladder is contracted, the contraction of the bladder is released and the oil in the shell is discharged into the pipeline 22.

[0031] In addition, the filling or discharge of the gas from the bladder can be performed through a valve (not illustrated). Incidentally, the accumulator is not limited to a bladder type as in the present embodiment, and may be of a piston type or may be changed as appropriate.

[0032] The pipeline 22 is further branched in two directions, and is also connected to the pressure sensor 6 and the electromagnetic switching valve 7.

[0033] The pressure sensor 6 is electrically connected to the control device 10 through an electrical signal line 15. The pressure sensor 6 detects the pressure in the pipeline 22, and outputs a pressure signal capable of specifying the pressure to the electrical signal line 15. The pressure in the pipeline 22 is substantially the same as the pressure of the oil accumulated under pressure in the accumulator 5.

[0034] The electromagnetic switching valve 7 is a spring-offset type two-position, two-port electromagnetic switching valve. The electromagnetic switching valve 7 in an offset position 7-1 prevents communication between the pipeline 21 and the pipeline 22.

[0035] In addition, the solenoid of the electromagnetic switching valve 7 is electrically connected to the control device 10 through an electrical signal line 16. In the electromagnetic switching valve 7, when the solenoid is energized by an electrical signal applied through the electrical signal line 16, a spool moves and switches to an onset position 7-2.

[0036] The electromagnetic switching valve 7 in the onset position 7-2 connects the pipelines 21 and 22 to allow the oil to pass from the pipeline 22 side to the pipeline 21. Accordingly, the oil discharged from the accumulator 5 can be supplied to the hydraulic pressure supplied circuit 8. At this time, the control device 10 sets the direction switching valve 3 to the neutral position 3-1.

[0037] In addition, when an operation command is input, the control device 10 outputs an electrical signal to the electrical signal line 14.

[0038] In the direction switching valve 3, when the solenoid 3b is energized by an electrical signal applied through the electrical signal line 14, a spool moves in a right direction and switches to a left position 3-3. The direction switching valve 3 in the left position 3-3 connects the pipeline 18 to the pipeline 21, and connects the pipeline 19 to the pipeline 20.

[0039] The pipeline 21 is branched in two directions, and is connected to the electromagnetic switching valve 7 and the hydraulic pressure supplied circuit 8. Accordingly, the oil delivered from the hydraulic pump 2 flows into the hydraulic pressure supplied circuit 8.

[0040] The hydraulic pressure supplied circuit 8 is a circuit in which a load is provided. Incidentally, the load may be an actuator such as a hydraulic cylinder or a hydraulic motor, or may be a pressure increasing device, a power generation device, or the like, and may be changed as appropriate.

[0041] Next, a fluid machine state monitoring apparatus 102 of the present embodiment will be described. The fluid machine state monitoring apparatus 102 is mainly composed of the pressure sensor 6 serving as a pressure detection device, the control device 10 serving as an output device, and the monitor 11 serving as a notification device.

[0042] The control device 10 estimates the sealed gas pressure in the accumulator 5 based on the pressure value inside the accumulator 5 input from the pressure sensor 6, and outputs, as the determination result, the ratio of the estimated sealed gas pressure to an appropriate sealed gas pressure, such as the sealed gas pressure when fully filled, that is, at the time of factory shipment, or when refilled with the sealed gas, to the monitor 11 through an electrical signal line 17. Hereinafter, a diagnostic procedure for the accumulator 5 by the fluid machine state monitoring apparatus 102 will be described with reference to FIGS. 2 and 3.

[0043] Incidentally, the sealed gas pressure in this specification refers to gas pressure in a state in which no oil flows into the accumulator 5. On the other hand, the sealed gas pressure may be the pressure in a state in which the accumulator 5 is fully filled with the oil, and may be changed as appropriate as long as the sealed gas pressure is a reference gas pressure detected under the same conditions.

[0044] As illustrated in FIG. 2, the control device 10 repeatedly executes step S1 until the control device 10 outputs an electrical signal to the electrical signal line 13 (step S1: N). When the pressure detected by the pressure sensor 6 increases to a certain level or higher, it is determined that pressure accumulation is in progress (step S1: Y), and the process proceeds to step S2.

[0045] Incidentally, regarding the method for determining whether pressure accumulation is in progress, the control device 10 may determine that pressure accumulation is in progress by outputting an electrical signal to the electrical signal line 13, or the method may be changed as appropriate.

[0046] When the process proceeds to step S2, the control device 10 receives pressure values sampled every 2 msec by the pressure sensor 6, and derives absolute pressure values at a predetermined frequency by performing a fast Fourier transform (hereinafter, referred to as "FFT') on waveforms obtained from the pressure values.

[0047] Incidentally, the waveforms illustrated in FIGS. 3A, 3C, and 3E that are formed by detection values sampled every 2 msec by the pressure sensor 6 are detection results by the pressure detection device of the present invention, and in more detail, the waveform in the period from 0.00 sec, which is the start time of step S2, to 0.10 sec is regarded as one detection result. The control device 10 performs an FFT on the one detection result. The same applies to step S4 to be described later.

[0048] For details regarding steps S2 and S4, referring to FIGS. 3A, 3C, and 3E, it can be seen that the pressure value input from the pressure sensor 6 to the control device 10 during pressure accumulation changes in a waveform over time. In addition, it can be confirmed that there is a regularity in which a plurality of consecutive cycles with large amplitude are followed by one cycle with small amplitude. That is, it can be seen that the oil delivered from the hydraulic pump 2 pulsates.

[0049] It has been found that the pulsation of the oil delivered from the hydraulic pump 2 has a frequency inherent to the pump. When the frequency of the hydraulic pump 2 is measured in a state in which the hydraulic circuit 101 is configured, a predetermined frequency to be measured can be specified. Specifically, in experiments to be described later, when the hydraulic pump 2 having a pulsation of 225 Hz was used, the predetermined frequency was approximately 223.1 Hz (see FIGS. 3B, 3D, and 3F).

[0050] It has been found through experiments that the absolute pressure value at the predetermined frequency and the sealed gas pressure show a correlation such that the absolute pressure value at the predetermined frequency increases as the sealed gas pressure decrease. FIG. 3 collectively illustrates one example of the experimental results.

[0051] Incidentally, FIGS. 3A, 3C, and 3E illustrate changes in pressure detected by the pressure sensor 6 in order to clearly illustrate increases and decreases in pressure, and the units or scales of pressure are the same. That is, the units or scales of pressure on the vertical axis are matched and displayed.

[0052] FIG. 3A illustrates the waveform of pressure values obtained as a detection result by the pressure sensor 6 when the hydraulic pump 2 is operated with the sealed gas pressure set to 2.0 MPa. FIG. 3B illustrates the absolute pressure value, that is, the amplitude extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3A. The absolute pressure value at the predetermined frequency was approximately 0.015 MPa.

[0053] FIG. 3C illustrates the waveform of pressure values obtained as a detection result when the sealed gas pressure is set to 1.8 MPa. FIG. 3D illustrates the absolute pressure value extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3C. The absolute pressure value at the predetermined frequency was approximately 0.019 MPa.

[0054] FIG. 3E illustrates the waveform of pressure values obtained as a detection result when the sealed gas pressure is set to 1.6 MPa. FIG. 3F illustrates the absolute pressure value extracted in the vicinity of the predetermined frequency that is obtained by performing an FFT on the waveform illustrated in FIG. 3E. The absolute pressure value at the predetermined frequency was approximately 0.022 MPa.

[0055] From above description, the correlation between the absolute pressure value at the predetermined frequency and the sealed gas pressure in the bladder is clear. Therefore, the absolute pressure value at the predetermined frequency obtained in a state in which the bladder is fully filled with gas is used as a set value, and the set value is compared with the absolute pressure value at the predetermined frequency obtained in step S2 (step S3).

[0056] If the absolute pressure value at the predetermined frequency obtained in step S2 is less than or equal to the set value, it is determined that the bladder is fully filled with gas (step S3: N). Next, the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display 100%.

[0057] Incidentally, here, 100% refers the ratio when the sealed gas pressure when fully filled is equal to the estimated sealed gas pressure. In addition, the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled is defined as 0% when the estimated sealed gas pressure is equal to atmospheric pressure. The sealed gas pressure when fully filled is a predetermined reference value in the present invention.

[0058] In addition, regarding the comparison between the absolute pressure value at the predetermined frequency and the set value, it may be determined whether the absolute pressure value at the predetermined frequency is included within a certain range including the set value, for example, within a range of ± 5% of the set value, or may be changed as appropriate.

[0059] Thereafter, the control device 10 ends the diagnosis of the accumulator 5. After the diagnosis is ended, if pressure accumulation is in progress (step S1: Y), steps S2 and S3 are newly executed.

[0060] Meanwhile, if the absolute pressure value at the predetermined frequency obtained in step S2 is larger than the set value, it can be estimated that an abnormality such as gas leakage or deterioration of the bladder has occurred (step S3: Y). In this case, pressure values newly sampled every 2 msec by the pressure sensor 6 are input, and an FFT is performed on a waveform obtained from the pressure values to specify an absolute pressure value at the predetermined frequency (step S4).

[0061] In step S5, the control device 10 compares the set value and the absolute pressure value at the predetermined frequency obtained in step S4. If the absolute pressure value at the predetermined frequency obtained in step S4 is less than or equal to the set value (step S5: N), the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display 100%. Thereafter, the diagnosis of the accumulator 5 is ended.

[0062] If the absolute pressure value at the predetermined frequency obtained in step S4 is larger than the set value (step S5: Y), the control device 10 proceeds to step S6.

[0063] In step S6, the control device 10 looks up the absolute pressure value at the predetermined frequency obtained in step S2 in a table (not illustrated), and specifies a corresponding pressure value set in advance based on experimental results or the like. Similarly, the absolute pressure value at the predetermined frequency obtained in step S4 is looked up in the same table to specify the corresponding pressure value. Then, an average value is calculated from each pressure value specified from the absolute pressure value at the predetermined frequency in each of steps S2 and S4. The average value is specified as the estimated sealed gas pressure.

[0064] Incidentally, the present invention is not limited to a configuration in which the absolute pressure value at the predetermined frequency is looked up in the table to specify the corresponding pressure value, and a configuration in which the corresponding pressure value is calculated by substituting the absolute pressure value at the predetermined frequency into an equation may be employed, and the method for specifying the estimated sealed gas pressure may be changed as appropriate.

[0065] In step S7, the control device 10 calculates the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled.

[0066] Thereafter, the control device 10 proceeds to step S8, and outputs an electrical signal to the monitor 11 to display the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled, for example, 70%. Accordingly, it is possible to grasp the extent to which the estimated sealed gas pressure is located relative to the sealed gas pressure when fully filled, that is, the degree of normality or abnormality.

[0067] In addition, in step S8, the control device 10 also outputs an electrical signal to the monitor 11 to display the ratio of the minimum value of the sealed gas pressure, at which the accumulator 5 is safely operable, to the sealed gas pressure when fully filled, for example, 60%. Accordingly, it is possible to grasp the extent to which the sealed gas pressure estimated from the waveform of hydraulic pressure is located relative to the minimum value at which the accumulator 5 is safely operable, that is, the degree of normality or abnormality.

[0068] Incidentally, the ratio of the minimum value, at which the accumulator 5 is safely operable, to the sealed gas pressure when fully filled may also be displayed on the monitor 11 when the conditions in step S3 or step S5 are not satisfied (S3, S5: N).

[0069] Furthermore, if the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled is 100%, the monitor 11 or a light-emitting device (not illustrated) such as a light bulb may be caused to emit blue light, if the ratio falls below 90%, the monitor 11 or the light-emitting device may be caused to emit yellow light, and if the ratio falls below 70%, the monitor 11 or the light-emitting device may be caused to emit red light.

[0070] In addition, an alarm corresponding to the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled may be sounded, or an alarm may be sounded for a period of time corresponding to the ratio. That is, the notification mode may be changed as appropriate as long as it is possible to grasp the extent to which the estimated sealed gas pressure is located relative to the minimum value at which the accumulator 5 is safely operable.

[0071] As described above, the fluid machine state monitoring apparatus 102 of the present embodiment can accurately diagnose the state of the accumulator 5 by determining the absolute pressure value at the predetermined frequency.

[0072] In addition, the absolute pressure value at the predetermined frequency changes in accordance with the sealed gas pressure, whereas the absolute pressure value at the predetermined frequency is hardly affected by the pressure accumulation state of the accumulator 5. Therefore, whether the accumulator is the accumulator 5 for pressure accumulation as in the present embodiment or the accumulator for pulsation prevention as in Patent Citation 1, the state of the accumulator can be accurately diagnosed.

[0073] In addition, the absolute pressure value at the predetermined frequency changes in accordance with the sealed gas pressure, whereas the absolute pressure value at the predetermined frequency is hardly affected by the amount of delivery per unit time from the hydraulic pump 2. Therefore, even when the amount of delivery per unit time is changed, that is, even when the pump is changed, the absolute pressure value at the predetermined frequency is not affected, and for example, even when the pump is replaced with a pump with different delivery performance, the state of the accumulator 5 can be accurately diagnosed.

[0074] In addition, since the predetermined frequency of the present embodiment is a natural frequency based on the characteristics of the hydraulic pump 2, the accuracy of the determination can be simply improved.

[0075] In addition, since the pressure sensor 6 samples pressure values every 2 msec less than or equal to 20 msec, the state of the accumulator 5 that is affected by the characteristics of the hydraulic pump 2 can be more accurately monitored.

[0076] Incidentally, the pressure sensor 6 preferably samples pressure values every 20 msec or less, and more preferably every 1 to 3 msec. The reason is that the shorter the sampling interval is, the easier it becomes to specify absolute pressure values at higher frequencies using FFT.

[0077] In addition, the fluid machine state monitoring apparatus 102 determines the maximum pressure value at the predetermined frequency at the timing at which the hydraulic pump 2 and the accumulator 5 are connected in the circuit. During pressure accumulation when the amount of delivery from the hydraulic pump 2 substantially coincides with the amount supplied to the accumulator 5 side, the behavior of the accumulator 5 is more likely to be stable, thereby allowing consistent behavior with less noise to be obtained, and enabling easier determination, compared to during discharge when the accumulator 5 is affected by the operating status on the hydraulic pressure supplied circuit 8 side, thereby making it difficult to obtain consistent behavior, and resulting in unstable behavior, such as intermittent operation. Accordingly, the state of the accumulator 5 can be more accurately monitored.

[0078] In addition, in the present embodiment, in diagnosing the accumulator 5, the absolute pressure value at the predetermined frequency is determined in steps S2 and S3, and the absolute pressure value at the predetermined frequency is further determined in steps S4 and S5. For example, even when an irregularity such as an impact occurs in steps S2 and S3 and the process proceeds to step S4, the absolute pressure value at the predetermined frequency in a state in which no irregularity is included can be obtained and determined in steps S4 and S5. Accordingly, the accuracy of the determination result can be improved.

[0079] In addition, since the average value of the pressure value corresponding to the absolute pressure value at the predetermined frequency specified in step S2 and the pressure value corresponding to the absolute pressure value at the predetermined frequency specified in step S4 is specified as the estimated sealed gas pressure, it is easier to reduce the error between the estimated sealed gas pressure and the actual sealed gas pressure compared to a configuration in which only one of the pressure values is adopted.

[0080] Incidentally, in the present embodiment, the output device has been described as being configured to make an operator recognize the determination result through display, sound, or the like; however, the present invention is not limited thereto. For example, a configuration in which the determination result is to restrict the direction switching valve 3 from switching to the right position 3-2 may be employed, and the method may be changed as appropriate.{Second embodiment}

[0081] Next, a fluid machine state monitoring apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. Incidentally, the description of configurations that are the same as and overlap with the configurations of the first embodiment will be omitted.

[0082] As illustrated in FIG. 4, a fluid machine state monitoring apparatus 202 provided in a hydraulic circuit 201 of the second embodiment is mainly composed of a pressure sensor 106 serving as the pressure detection device, the control device 10, and the monitor 11.

[0083] The pressure sensor 106 is connected to the accumulator 5. In addition, the pressure sensor 106 is electrically connected to the control device 10 through an electrical signal line 115. The pressure sensor 106 detects the gas pressure in the bladder, and outputs a pressure signal capable of specifying the gas pressure to the electrical signal line 115.

[0084] As illustrated in FIG. 5, it can be seen that the pressure value input from the pressure sensor 106 to the control device 10 during pressure accumulation changes in a waveform over time. That is, it can be seen that the gas sealed in the bladder is affected by the pulsation of the oil delivered from the hydraulic pump 2. In more detail, it can be seen that the gas pressure also changes in the same manner as the hydraulic pressure in the accumulator 5 changes. That is, the pressure sensor 106 can detect changes in hydraulic pressure from changes in gas pressure.

[0085] Accordingly, similarly to the first embodiment, the control device 10 can derive an absolute pressure value at a predetermined frequency by performing an FFT on a waveform obtained from a plurality of pressure values input from the pressure sensor 106.

[0086] Incidentally, the absolute pressure value at the predetermined frequency derived by performing an FFT on the waveform obtained from the pressure values detected by the pressure sensor 106 as in the present embodiment and the absolute pressure value at the predetermined frequency derived by performing an FFT on the waveform obtained from the pressure values detected by the pressure sensor 6 as in the first embodiment may be used in combination. That is, two pressure sensors 6 and 106 may be used in combination as the pressure detection device.

[0087] The embodiments of the present invention have been described above with reference to the drawings; however, the specific configurations are not limited to these embodiments, and modifications or additions that are made without departing from the scope of the present invention are also included in the present invention.

[0088] For example, in the first and second embodiments, the fluid pressure circuit has been described as a hydraulic circuit in which oil is pumped; however, the present invention is not limited thereto. The working fluid may be a fluid other than oil, and the fluid to be applied may be changed as appropriate.

[0089] In addition, in the first and second embodiments, a configuration in which the working fluid delivered from the pump is directly supplied to the pressure accumulator has been described; however, the present invention is not limited thereto, and a configuration in which an actuator is provided between the pump and the pressure accumulator and the working fluid delivered from the actuator is supplied to the pressure accumulator may be employed. Even with such a configuration, the state of the pressure accumulator can be diagnosed by specifying a predetermined frequency in the fluid pressure circuit and obtaining a pressure at the frequency.

[0090] In addition, in the first and second embodiments, an example of the type of pressure accumulator that accumulates the working fluid, which is delivered from the pump, under pressure in order to discharge the working fluid when needed has been provided; however, the present invention is not limited thereto, and the pressure accumulator may be used for pulsation prevention or may be used for energy regeneration. In addition, the pressure accumulator in the present invention may be any device capable of temporarily storing and discharging the working fluid, such as an air chamber or a damper, and may be changed as appropriate.

[0091] In addition, in the first and second embodiments, a configuration in which the state of the pressure accumulator is diagnosed based on the pulsation during pressure accumulation has been described; however, the present invention is not limited thereto, and the diagnosis may be performed based on the pulsation during discharge or the pulsation in a constant-pressure state.

[0092] In addition, in the first and second embodiments, the determination result has been described as the ratio of the estimated sealed gas pressure to the sealed gas pressure when fully filled; however, the present invention is not limited thereto. The determination result may be the absolute pressure value at the predetermined frequency, may be the estimated sealed gas pressure itself, may be the amount of sealed gas corresponding to the estimated sealed gas pressure, or may be the ratio of the estimated amount of sealed gas to the amount of sealed gas when fully filled, the ratio of the estimated sealed gas pressure to the minimum value for safe operation may be output as the determination result, or the determination result may simply be whether the sealed gas pressure has decreased, and the type of determination result may be changed as appropriate.

[0093] In addition, in the first and second embodiments, a configuration in which when it is determined that the absolute pressure value at the predetermined frequency is larger than the set value in two consecutive instances, it is diagnosed that an abnormality has occurred in the pressure accumulator has been described; however, the present invention is not limited thereto. When it is determined that the absolute pressure value at the predetermined frequency is larger than the set value in three or more consecutive instances, it may be diagnosed that an abnormality has occurred in the pressure accumulator, or when it is determined once that the absolute pressure value at the predetermined frequency is larger than the set value, it may be diagnosed that an abnormality has occurred in the pressure accumulator, and the determination criteria may be changed as appropriate.

[0094] In addition, in the first and second embodiments, a configuration in which an average value is calculated from each pressure value specified from the absolute pressure values at the predetermined frequency detected two times has been described; however, the present invention is not limited thereto. A pressure value that are considered to strongly reflect irregularities may be excluded from the plurality of specified pressure values using a filter, or any value other than the average value may be used as long as the influence of irregularities can be reduced.

[0095] In addition, in the first and second embodiments, the pressure detection device has been described as being configured as a pressure sensor; however, the present invention is not limited thereto, and the pressure detection device may be composed of a pressure sensor and a control device. That is, a configuration in which the control device samples pressure data, which is sequentially input to the control device from the pressure sensor, at predetermined time intervals to obtain a pressure value may be employed.

[0096] In addition, in the first and second embodiments, one detection result has been described as a plurality of pressure values constituting a waveform from 0.00 sec to 0.10 sec; however, the present invention is not limited thereto. As long as the pressure at the predetermined frequency can be specified, one detection result may be one pressure value, may be a plurality of pressure values corresponding to one cycle, may be a plurality of pressure values corresponding to a predetermined plurality of cycles, may be a plurality of pressure values obtained per another unit time, or the detection result may be changed as appropriate. In addition, from the viewpoint of being able to reduce the influence of irregularities, a larger number of cycles is preferable.

[0097] In addition, in the first and second embodiments, the control device serving as the output device has been described as being configured to also control the direction switching valve, the electromagnetic switching valve, and the like; however, the present invention is not limited thereto. The control device may be provided separately from a control device that controls the direction switching valve, the electromagnetic switching valve, and the like, and may be, for example, a cloud server or the like. If the output device is configured as a cloud server, the pressure detection device or the notification device may be wirelessly connected to the cloud server. In other words, the pressure detection device or the notification device may include a communication device.

[0098] Further, the notification device may be a smartphone or a tablet terminal. With such a configuration, the determination result may be transmitted from the cloud server as a notification or email, or a user may access the cloud server and receive the determination result, and the notification method may be changed as appropriate. In addition, if the pressure detection device includes a wireless communication device, a microcontroller, which is an output device, or the like, the determination result may be output to the cloud server.

[0099] In addition, in the first and second embodiments, tests were performed at room temperature; however, in consideration of climate or temperature changes to which the internal fluid is subjected, values obtained by applying temperature correction to the test results may be used.{REFERENCE SIGNS LIST}

[0100] 2Hydraulic pump (pump) 5Accumulator (pressure accumulator) 6Pressure sensor (pressure detection device) 8Hydraulic pressure supplied circuit (supply destination) 10Control device (output device) 11Monitor (notification device) 101Hydraulic circuit (fluid pressure circuit) 102fluid machine state monitoring apparatus 106Pressure sensor (pressure detection device) 201Hydraulic circuit (fluid pressure circuit) 202fluid machine state monitoring apparatus

Examples

first embodiment

{First embodiment}

[0019]A fluid pressure circuit to which a fluid machine state monitoring apparatus according to a first embodiment of the present invention is applied will be described with reference to FIGS. 1 to 3. In the following description, the right and left sides when viewed from the front of FIG. 1 correspond to the right and left sides of the valve position of an electromagnetic direction switching valve.

[0020]A hydraulic circuit serving as the fluid pressure circuit according to the first embodiment delivers oil serving as a working fluid to a supply destination in response to a command in work machines, construction machines, cargo handling vehicles, automobiles, electric trains, wind power generation systems, or the like.

[0021]As illustrated in FIG. 1, a hydraulic circuit 101 is mainly composed of a drive mechanism 1, a hydraulic pump 2, an electromagnetic direction switching valve 3 (hereinafter, referred to as the direction switching valve 3), a check valve 4, an ac...

second embodiment

{Second embodiment}

[0081]Next, a fluid machine state monitoring apparatus according to a second embodiment of the present invention will be described with reference to FIGS. 4 and 5. Incidentally, the description of configurations that are the same as and overlap with the configurations of the first embodiment will be omitted.

[0082]As illustrated in FIG. 4, a fluid machine state monitoring apparatus 202 provided in a hydraulic circuit 201 of the second embodiment is mainly composed of a pressure sensor 106 serving as the pressure detection device, the control device 10, and the monitor 11.

[0083]The pressure sensor 106 is connected to the accumulator 5. In addition, the pressure sensor 106 is electrically connected to the control device 10 through an electrical signal line 115. The pressure sensor 106 detects the gas pressure in the bladder, and outputs a pressure signal capable of specifying the gas pressure to the electrical signal line 115.

[0084] As illustrated in FIG. 5, it can b...

Claims

1. A fluid machine state monitoring apparatus which is used for a fluid pressure circuit including a pump and a pressure accumulator, and which is configured to diagnose a state of the pressure accumulator, comprising: a pressure detection device configured for detecting a pressure of a working fluid in the fluid pressure circuit; and an output device configured for outputting a determination result at a predetermined frequency among detection results from the pressure detection device.

2. The fluid machine state monitoring apparatus according to claim 1, wherein the predetermined frequency is a unique frequency determined by characteristics of the pump.

3. The fluid machine state monitoring apparatus according to claim 1 or 2, wherein the pressure detection device is configured to sample the pressure every 20 msec or less.

4. The fluid machine state monitoring apparatus according to claim 3, wherein the pressure detection devices is configured to sample the pressure every 1 to 3 msec.

5. The fluid machine state monitoring apparatus according to claim 1, wherein the output device is configured to perform a determination at the predetermined frequency at a timing at which the pump and the pressure accumulator are connected.

6. The fluid machine state monitoring apparatus according to claim 1, wherein the determination result is obtained from the pressures at the predetermined frequency detected a plurality of times.

7. The fluid machine state monitoring apparatus according to claim 1, wherein the pressure detection device is configured to directly detect a working fluid pressure of the pressure accumulator, and the output device is configured to output, as the determination result, a result determined with respect to a predetermined reference value.

8. The fluid machine state monitoring apparatus according to claim 7, wherein the output device is configured to output, as the determination result, a result determined with respect to a minimum value for a safe operation.

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