Pump calibration system and pump calibration method

Abstract

To provide a pump calibration system that can easily calibrate a pump characteristic indicating the relationship between a signal and the discharge capacity of a hydraulic pump.SOLUTION: A pump calibration system includes a hydraulic pump of a variable capacity type, a regulator that changes a discharge capacity of the hydraulic pump according to a command signal, an unloader valve having a variable opening degree, a pressure sensor that measures a discharge pressure of the hydraulic pump, and a control device that controls the discharge capacity and calibrates a pump characteristic. The control device is configured to: store, in advance, a first reference pressure detected by the pressure sensor when a predetermined first reference signal is output to the regulator under measurement conditions that the opening degree of the unloader valve should be fixed to a predetermined value and that the hydraulic pump should be driven to rotate at a predetermined number of revolutions; and, when a predetermined calibration condition is satisfied, change the command signal that is output to the regulator so that the discharge pressure detected by the pressure sensor under the measurement conditions becomes the first reference pressure; and calibrate the pump characteristic on the basis of a first actual signal that is the command signal with which the discharge pressure is the first reference pressure.SELECTED DRAWING: Figure 1

Description

TECHNICAL FIELD

[0001] The present invention relates to a pump calibration system that calibrates pump characteristics representing the relationship between the discharge capacity of a hydraulic pump and a signal. BACKGROUND ART

[0002] Variable displacement hydraulic pumps that change discharge capacity based on a current command value are employed in hydraulic pumps installed in construction machinery, industrial machinery, and the like. In a variable displacement hydraulic pump, the discharge capacity is changed in accordance with a current command value output according to current-flow rate characteristics (that is, I-q characteristics, which are pump characteristics). However, the current-flow rate characteristics change when parts are replaced or the like. As a result, hydraulic fluid at a desired flow rate cannot be discharged from the hydraulic pump. Therefore, it is preferable to calibrate the current-flow rate characteristics.

[0003] In the calibration system of Patent Document 1, pump pressure is measured for each of multistage-changed current command values. Further, in the calibration system, a coefficient indicating the relationship between pump pressure and pump flow rate is calculated for each pump pressure. Furthermore, in the calibration system, each pump pressure is converted into a pump flow rate using the coefficient. Then, in the calibration system, the current-flow rate characteristics are calibrated by associating the converted pump flow rate with the current command value. PRIOR ART DOCUMENT PATENT DOCUMENT

[0004] Patent Document 1 Japanese Unexamined Patent Publication No. 2019-190443 SUMMARY OF THE INVENTION PROBLEM TO BE SOLVED BY THE INVENTION

[0005] As mentioned above, the calibration system in Patent Document 1 requires multiple steps, including measuring pump pressure, calculating coefficients, and converting them to flow rates. However, there is a need for a simpler calibration method for current-flow characteristics. In other words, there is a desire for a pump calibration system that facilitates the calibration of pump characteristics, which show the relationship between the discharge capacity of a hydraulic pump and the current (i.e., the command signal).

[0006] Therefore, the present invention aims to provide a pump calibration system that can easily calibrate the pump characteristics, which show the relationship between the discharge capacity of a hydraulic pump and the command signal. [Means for solving the problem]

[0007] The pump calibration system of the present invention comprises a variable displacement hydraulic pump capable of changing the discharge capacity, a regulator that changes the discharge capacity of the hydraulic pump according to an input command signal, an unload valve disposed between the hydraulic pump and a tank and whose opening degree can be changed, a pressure sensor that measures the discharge pressure of the hydraulic pump, and a control device that controls the discharge capacity of the hydraulic pump by outputting a command signal to the regulator and calibrates the pump characteristics that show the relationship between the command signal and the discharge capacity or discharge flow rate of the hydraulic pump. The control device stores in advance the pressure detected by the pressure sensor as the first reference pressure when a predetermined first reference signal is output to the regulator under measurement conditions in which the opening degree of the unload valve is fixed to a predetermined value and the hydraulic pump is driven to rotate at a predetermined rotational speed, and when predetermined calibration conditions are met, it changes the command signal output to the regulator in order to make the discharge pressure detected by the pressure sensor under the measurement conditions the first reference pressure, and calibrates the pump characteristics based on the first actual signal, which is the command signal when the discharge pressure becomes the first reference pressure.

[0008] According to the present invention, pump characteristics can be calibrated based on stored pump characteristics. The pump characteristics are calibrated based on a first actual signal that has the same discharge pressure as the discharge pressure detected when the first reference signal is output. Therefore, pump characteristics can be easily calibrated without using a flow meter.

[0009] The pump calibration method of the present invention is a method for calibrating pump characteristics that show the relationship between a command signal input to a regulator when the regulator changes the discharge capacity of a variable displacement hydraulic pump and the discharge capacity or discharge flow rate, and comprises: a first reference pressure detection step of storing a first reference pressure detected by a pressure sensor when the regulator changes the discharge capacity of the hydraulic pump in response to a first reference signal input under predetermined measurement conditions in which the opening degree of an unload valve disposed between the hydraulic pump and a tank is fixed to a predetermined value; a first actual signal derivation step of changing the command signal output to the regulator under the measurement conditions and deriving a first actual signal which is a command signal when the discharge pressure becomes the first reference pressure; and a calibration step of calibrating the pump characteristics based on the first actual signal, wherein in the first reference pressure detection step the first reference pressure is detected before the predetermined calibration conditions are satisfied, and in the first actual signal derivation step the command signal output to the regulator is changed after the calibration conditions are satisfied and the first actual signal is derived.

[0010] According to the present invention, a first reference pressure is detected before the calibration conditions are met, and after the calibration conditions are met, the signal output to the regulator is changed to make the discharge pressure equal to the first reference pressure, thereby producing a first actual signal. Therefore, the pump characteristics after the calibration conditions are met can be calibrated using the pump characteristics before the calibration conditions are met as a reference. As a result, the pump characteristics are calibrated based on a first actual signal that has the same discharge pressure as the discharge pressure detected when the first reference signal is output. Therefore, the pump characteristics can be easily calibrated without using a flow meter. [Effects of the Invention]

[0011] According to the present invention, the pump characteristics, which show the relationship between the discharge capacity of a hydraulic pump and the command signal, can be easily calibrated. [Brief explanation of the drawing]

[0012] [Figure 1] This is a circuit diagram showing a hydraulic drive system equipped with a pump calibration system according to the first embodiment. [Figure 2] This graph shows the pump characteristics of the regulator included in the pump calibration system shown in Figure 1. [Figure 3] This is a flowchart showing the procedure for the pump calibration method performed in the pump calibration system shown in Figure 1. [Figure 4] Figure 1 shows a graph illustrating the relationship between discharge pressure and command signal in the pump calibration system. [Figure 5] This is a flowchart showing the procedure for the pump calibration method performed in the pump calibration system of the second embodiment. [Figure 6] This graph shows the relationship between discharge pressure and command signal in the pump calibration system of the second embodiment. [Figure 7] This graph shows the pump characteristics of the regulator included in the pump calibration system of the second embodiment. [Modes for carrying out the invention]

[0013] Hereinafter, the pump calibration systems 1 and 1A of the first and second embodiments of the present invention will be described with reference to the aforementioned drawings. Note that the concept of direction used in the following description is for convenience of explanation and does not limit the orientation of the invention's configuration to that direction. Furthermore, the pump calibration systems 1 and 1A described below are merely one embodiment of the present invention. Therefore, the present invention is not limited to these embodiments, and additions, deletions, and modifications are possible without departing from the spirit of the invention.

[0014] <First Embodiment> The pump calibration system 1 shown in Figure 1 is installed, for example, in a hydraulic machine (not shown). The hydraulic machine is a work vehicle such as a construction vehicle such as a hydraulic excavator and hydraulic crane, and an industrial vehicle such as a lift. Note that the hydraulic machine is not limited to work vehicles, but may also be agricultural machinery, ships, hydrogen-related machinery, medical machinery, etc. The hydraulic machine comprises at least one actuator 2 and a hydraulic drive system 3 including the pump calibration system 1. The actuator 2 is, for example, a hydraulic cylinder and a hydraulic motor. The hydraulic drive system 3 supplies and discharges working fluid to the actuator 2. As a result the actuator 2 is operated, the hydraulic machine can perform various tasks. More specifically, the hydraulic drive system 3 comprises a hydraulic pump 11, a regulator 12, a hydraulic circuit 13, an unload valve 14, a pressure sensor 15, and a control device 16. The pump calibration system 1 comprises at least a hydraulic pump 11, a regulator 12, an unload valve 14, a pressure sensor 15, and a control device 16.

[0015] The hydraulic pump 11 is rotationally driven by a drive source (e.g., an engine or electric motor) 10. By being rotationally driven, the hydraulic pump 11 discharges working fluid into the pump passage 11a. The hydraulic pump 11 is a variable displacement pump. In this embodiment, the hydraulic pump 11 is a variable displacement swashplate pump, and the discharge volume is changed by tilting the swashplate 11b. The hydraulic pump 11 may also be a variable displacement oblique shaft pump, or any pump that can change the discharge volume and discharge working fluid.

[0016] The regulator 12 changes the discharge capacity of the hydraulic pump 11 in accordance with an input command signal. In the present embodiment, the command signal is a current signal. However, the signal is not limited to a current signal, and may be a voltage signal or a CAN signal. The regulator 12 includes, for example, a servo piston 12a and an electromagnetic proportional valve 12b. The servo piston 12a is connected to a swash plate 11b. The servo piston 12a moves to a position corresponding to an input pilot pressure. Then, the movement of the servo piston 12a tilts the swash plate 11b. Accordingly, the discharge capacity of the hydraulic pump 11 is adjusted to a capacity corresponding to the input pilot pressure. Although discharge pressure is guided to the servo piston 12a, a passage that guides the discharge pressure is omitted in FIG. 1.

[0017] The electromagnetic proportional valve 12b outputs a pilot pressure corresponding to the command signal. More specifically, the electromagnetic proportional valve 12b is connected to, for example, a pilot pump 21, a tank 20, and the regulator 12. The electromagnetic proportional valve 12b outputs a pilot pressure corresponding to the command signal to the servo piston 12a by adjusting the opening degree of passages respectively connected to the pilot pump 21 and the tank 20. The pilot pressure acts on the servo piston 12a against the discharge pressure guided to the servo piston 12a, and the servo piston 12a moves to a position corresponding to the pilot pressure. Accordingly, the discharge capacity of the hydraulic pump 11 changes. That is, the regulator 12 changes the discharge capacity of the hydraulic pump 11 in accordance with the command signal. The electromagnetic proportional valve 12b is not limited to the one described above as long as it can output a pilot pressure corresponding to the command signal.

[0018] The hydraulic circuit 13 is connected to the hydraulic pump 11 and at least one actuator 2, respectively. More specifically, the hydraulic circuit 13 is connected to the hydraulic pump 11 via the pump passage 11a. The hydraulic circuit 13 then guides the working fluid discharged from the hydraulic pump 11 to the actuator 2. The hydraulic circuit 13 also controls the flow of the working fluid from the hydraulic pump 11 to the actuator 2. The hydraulic circuit 13 is equipped with various valves, such as relief valves and control valves, and controls the flow of the working fluid by operating these various valves.

[0019] The unload valve 14 is positioned between the hydraulic pump 11 and the tank 20. The unload valve 14 can change the opening degree between the hydraulic pump 11 and the tank 20 (hereinafter referred to as "opening degree of the unload valve 14"). More specifically, the unload valve 14 is connected upstream of the hydraulic circuit 13 in the pump passage 11a. Alternatively, the unload valve 14 may be connected downstream of the hydraulic circuit 13 in the pump passage 11a. The unload valve 14 unloads the hydraulic pump 11 by discharging the working fluid discharged from the hydraulic pump 11 into the tank 20. In this embodiment, the unload valve 14 is a three-position spool valve. That is, the unload valve 14 has a spool 14a which is a valve body. The spool 14a moves to one of the first to third positions according to the input position signal. In the first position A1, the spool 14a fixes the opening degree of the unload valve 14 to a predetermined value. Furthermore, in the second position, the spool 14a blocks the connection between the hydraulic pump 11 and the tank 20. In addition, in the third position, the spool 14a changes the opening degree of the unload valve 14 according to the stroke amount. Note that the unload valve 14 is not limited to a 3-position spool valve, but may also be a 2-position spool valve.

[0020] The pressure sensor 15 measures the discharge pressure of the hydraulic pump 11. To explain in more detail, the pressure sensor 15 is connected to the pump passage 11a. In the present embodiment, the pressure sensor 15 is connected upstream of the unload valve 14 in the pump passage 11a. The pressure sensor 15 measures the pressure of the hydraulic fluid flowing through the pump passage 11a as the discharge pressure of the hydraulic pump 11.

[0021] The control device 16 acquires the discharge pressure of the hydraulic pump 11 from the pressure sensor 15. Then, the control device 16 controls the drive source 10, the regulator 12, the hydraulic circuit 13, and the unload valve 14. To explain in more detail, the control device 16 controls the regulator 12 by outputting a command signal to the regulator 12 in accordance with pump characteristics as shown by the solid line in Fig. 2. Note that the pump characteristics are a function indicating the relationship between the command signal (i.e., current) and the discharge capacity of the hydraulic pump 11. To explain in more detail, the pump characteristics are a function indicating the discharge capacity that the regulator 12 should control in response to the command signal. In the present embodiment, the pump characteristics are such that the discharge capacity when the command signal is the first reference signal I0 is the reference discharge capacity q0, and are stored in the control device 16 in advance, for example by measurement during manufacturing. The control device 16 controls the discharge capacity of the hydraulic pump 11 by outputting a command signal to the regulator 12 (the electromagnetic proportional valve 12b in the present embodiment) in accordance with the pump characteristics. Thereby, the discharge capacity of the hydraulic pump 11 is controlled in accordance with the command signal.

[0022] Further, the control device 16 outputs a position signal to the unload valve 14. Thereby, the position and stroke amount of the spool 14a are controlled. Then, the discharge amount of hydraulic fluid discharged from the hydraulic pump 11 to the tank 20 is controlled. Further, the control device 16 outputs a command to the hydraulic circuit 13. Thereby, the flow of hydraulic fluid flowing from the hydraulic pump 11 to the actuator 2 is controlled. Furthermore, the control device 16 controls the drive source 10. Thereby, the rotational speed of the hydraulic pump 11 is adjusted.

[0023] Furthermore, as described above, the control device 16, together with the hydraulic pump 11, regulator 12, unload valve 14, and pressure sensor 15, constitutes the pump calibration system 1. The control device 16 can calibrate the pump characteristics together with these components. More specifically, the control device 16 calibrates the pump characteristics by performing the pump calibration method which will be described in detail later.

[0024] The control device 16 includes a memory and a processor (not shown). The memory stores the detection results of the pressure sensor 15. The memory also stores various programs for controlling the operation of the regulator 12, the hydraulic circuit 13, and the unload valve 14, and for performing pump calibration methods. The processor then executes the programs stored in the memory to operate the regulator 12, the hydraulic circuit 13, and the unload valve 14, and to perform the pump calibration method.

[0025] <Pump Calibration Method> In the hydraulic drive system 3, the pump characteristics change due to parts replacement, aging, etc. Therefore, the pump calibration method calibrates the pump characteristics after satisfying predetermined calibration conditions. The predetermined calibration conditions are, for example, selecting a calibration mode. More specifically, the pump calibration system 1 is equipped with an input device (not shown). An operator can select the mode, either initial state memory mode or calibration mode, using the input device. The initial state memory mode is a mode that stores the state value (first reference pressure pd, described later in this embodiment) of the state before the calibration conditions are satisfied (in this embodiment, the initial state of the product, for example, the state at the time of manufacture). The calibration mode is a mode that calibrates the current pump characteristics according to the first reference pressure pd of the state before the calibration conditions are satisfied (in this embodiment, the initial state of the product). Note that the calibration conditions may also include, for example, the replacement of at least a part of the regulator 12. Furthermore, calibration conditions may include the fact that the hydraulic pump 11 has deteriorated over time (i.e., the hydraulic pump 11 has been in use for more than a specified number of years), that the hydraulic pump 11 has been replaced, and that maintenance work has been performed on the hydraulic pump 11 or the regulator 12.

[0026] In the pump calibration method, the pump characteristics are calibrated based on the state value at a point in time that is to be used as a reference for calibrating the pump characteristics, for example, the state before the calibration conditions are met. Therefore, in the pump calibration method, a first reference pressure pd is pre-stored as the state value at the time of manufacture of the hydraulic machine. Then, in the pump calibration method, when the predetermined calibration conditions are met, the pump characteristics are calibrated based on the first reference pressure pd. By determining that the calibration conditions have been met and calibrating the pump characteristics, the discharge capacity of the hydraulic pump 11 is controlled to the desired capacity. In such a pump calibration method, the pump characteristics are calibrated in the procedure shown in the flow chart of Figure 3. The procedure of the pump calibration method will be explained in detail below with reference to Figure 3.

[0027] More specifically, the pump calibration method is started by the control device 16 when a mode is selected via an input device (not shown). Once started, the process proceeds to step S1. Step S1, which is a calibration condition determination step, determines whether predetermined calibration conditions are met. More specifically, the control device 16 determines whether a calibration mode is selected. If the initial state storage mode is selected, the process proceeds to step S2. On the other hand, if the calibration mode is selected, the process proceeds to step S3.

[0028] In step S2, which is the first reference pressure detection process, a predetermined first reference signal I0 is input to the regulator 12 (more specifically, the electromagnetic proportional valve 12b) under predetermined measurement conditions, which are reference conditions (see the first reference signal I0 in the graph of Figure 4). The reference condition is to fix the opening degree of the unload valve 14 to a predetermined value. In this embodiment, under the reference condition, the spool 14a of the unload valve 14 is positioned at a first position A1, thereby fixing the opening degree of the unload valve 14 to a predetermined value, and the pump is operated at a desired rotational speed. More specifically, under the reference condition, the control device 16 maintains the rotational speed of the hydraulic pump 11 at a predetermined rotational speed. Furthermore, under the reference condition, the entire amount of working fluid from the hydraulic pump 11 is discharged from the unload valve 14 to the tank 20. For example, the control device 16 stops the outflow of working fluid from the hydraulic circuit 13 to the actuator 2, more specifically, it closes the various valves of the hydraulic circuit 13. Under these reference conditions, when the first reference signal I0 is input, the regulator 12 changes the discharge capacity of the hydraulic pump 11 in accordance with the first reference signal I0. The control device 16 then stores the first reference pressure pd detected by the pressure sensor 15 after changing the discharge capacity according to I0 (see the first reference pressure pd in Figure 4). The solid line in Figure 4 is a graph showing the change in discharge pressure when the command signal is changed under the reference conditions before the calibration conditions are met. Once the control device 16 has stored the first reference pressure pd, the pump calibration method ends. When a mode is selected again via the input device, the pump calibration method starts and proceeds to step S1.

[0029] In step S3, which is the first actual signal derivation process, the control device 16 changes the command signal under reference conditions (see arrow Y in Figure 4, for example). That is, the control device 16 changes the command signal from the first reference signal I0. As a result, the discharge pressure of the hydraulic pump 11 changes. By changing the discharge pressure, the control device 16 derives the first actual signal I1, which is the signal when the discharge pressure detected by the pressure sensor 15 becomes the first reference pressure pd (see first actual signal I1 in Figure 4). The dashed line in Figure 4 is a graph showing the change in discharge pressure when the command signal is changed under reference conditions after the calibration conditions have been met. Note that the relationship between current and discharge capacity at this time differs from the relationship stored in step S2 due to aging or changes in the regulator. Once the first actual signal I1 is derived, the process proceeds to step S4.

[0030] In step S4, which is a calibration process, the pump characteristics are calibrated based on the first real signal I1 (see the dashed line in Figure 2). More specifically, the control device 16 adjusts the command signal according to the difference between the first real signal I1 and the first reference signal I0 (see the dashed line in Figure 2). In this embodiment, the control device 16 uniformly adds the difference obtained by subtracting the first reference signal I0 from the first real signal I1 to the pump characteristics before calibration across the entire current range. That is, the control device 16 slides the pump characteristics before calibration by the difference described above (see arrow X in Figure 2). In both cases, the opening degree of the unload valve 14 is fixed to a predetermined value and the pressure before and after the unload valve 14 is the same. Therefore, in both cases, the flow rate passing through the unload valve 14 is equal. In other words, the first actual signal I1 derived in the first actual signal derivation step is a command signal input to the current regulator 12 (the regulator 12 after replacement in this embodiment) to set the discharge capacity of the hydraulic pump 11 to the reference discharge capacity q. Therefore, the pump characteristics can be calibrated so that the discharge capacity when the command signal is the first actual signal I1 becomes the reference discharge capacity q. Once the pump characteristics are calibrated, the pump calibration method is completed. After that, the control device 16 controls the discharge capacity of the hydraulic pump 11 using the calibrated pump characteristics.

[0031] In the pump calibration system 1 of this embodiment, pump characteristics can be calibrated based on stored pump characteristics. The pump characteristics are calibrated based on a first actual signal I1 that has the same discharge pressure as the discharge pressure detected when the first reference signal I0 is output. Therefore, pump characteristics can be calibrated with high accuracy and easily without using a flow meter.

[0032] Furthermore, in the pump calibration system 1 of this embodiment, the pump characteristics are calibrated according to the difference between the first real signal I1 and the first reference signal I0. Therefore, the pump characteristics can be calibrated even more easily.

[0033] Furthermore, in the pump calibration system 1 of this embodiment, the control device 16 moves the spool 14a of the unload valve 14 to a first position A1 that fixes the opening degree to a predetermined value under measurement conditions. Therefore, it is easy to maintain the opening degree to a predetermined value. This makes it easy to maintain the measurement conditions in order to detect the discharge pressure, i.e., to achieve reproducibility.

[0034] Furthermore, in the pump calibration method of this embodiment, a first reference pressure pd is detected before the calibration conditions are met, and after the calibration conditions are met, the signal output to the regulator 12 is changed to make the discharge pressure equal to the first reference pressure pd, thereby deriving a first actual signal I1. Therefore, the pump characteristics after the calibration conditions are met can be calibrated using the pump characteristics before the calibration conditions are met as a reference. As a result, the pump characteristics are calibrated based on the first actual signal, which has the same discharge pressure as the discharge pressure detected when the first reference signal is output. Therefore, the pump characteristics can be calibrated with high accuracy and easily without using a flow meter.

[0035] <Second Embodiment> The pump calibration system 1A of the second embodiment is provided in the hydraulic drive system 3, just like the pump calibration system 1 of the first embodiment, and has the same configuration as the pump calibration system 1 of the first embodiment. Therefore, the components of the pump calibration system 1A of the second embodiment are denoted by the same reference numerals as those of the pump calibration system 1 of the first embodiment, and their descriptions are omitted. On the other hand, the pump calibration method performed by the pump calibration system 1A of the second embodiment differs in part from the pump calibration method performed by the pump calibration system 1 of the first embodiment. The pump calibration method performed by the pump calibration system 1A of the second embodiment will be described below. Note that the explanation of the pump calibration method performed by the pump calibration system 1A of the second embodiment may be omitted if it is the same as the pump calibration method performed by the pump calibration system 1 of the first embodiment.

[0036] The pump calibration method shown in Figure 5 is also initiated by the control device 16 when an operator selects a mode via an input device (not shown). Once initiated, the process proceeds to step S11. In step S11, which is the calibration condition determination step, the control device 16 determines whether the selected mode is a calibration mode, similar to step S1. If it is the initial state memory mode, the process proceeds to step S12. On the other hand, if it is a calibration mode, the process proceeds to step S14.

[0037] In step S12, the first reference pressure detection step, a first reference signal I10 is input to the regulator 12 under reference conditions (see the first reference signal I10 in the graph in Figure 6). The control device 16 then stores the first reference pressure pd1 detected by the pressure sensor 15 after the first reference signal I10 is input to the regulator 12 and the discharge capacity is changed (see the first reference pressure pd1 in Figure 6). The solid line in Figure 6 is a graph showing the change in discharge pressure when the command signal is changed under reference conditions before the calibration conditions are met. The detection and storage of the first reference pressure pd1 are performed before the calibration conditions are met. Once the control device 16 has stored the first reference pressure pd1 in advance, the process proceeds to step S13.

[0038] In step S13, the second reference pressure detection step, a second reference signal I20 is input to the regulator 12 under reference conditions (see the second reference signal I20 in the graph in Figure 6). Note that the second reference signal I20 is a different signal from the first reference signal I10. In this embodiment, the second reference signal I20 is a signal with a different current value from the first reference signal I10. The control device 16 stores the second reference pressure pd2 detected by the pressure sensor 15 after the second reference signal I20 is input to the regulator 12 and the discharge capacity is changed (see the second reference pressure pd2 in Figure 6). Note that the detection and storage of the second reference pressure pd2 are also performed before the calibration conditions are met. Once the control device 16 has stored the second reference pressure pd2 in advance, the pump calibration method ends. Then, when a mode is selected again via the input device, the pump calibration method starts and proceeds to step S11.

[0039] In step S14, which is the first actual signal derivation process, the control device 16 changes the command signal from the first reference signal I10 under reference conditions (see arrow Y1 in Figure 6, for example). As a result, the discharge pressure of the hydraulic pump 11 changes. By changing the discharge pressure, the control device 16 derives the first actual signal I11, which is the signal when the discharge pressure detected by the pressure sensor 15 becomes the first reference pressure pd1 (see the first actual signal I11 in Figure 6). The dashed line in Figure 6 is a graph showing the change in discharge pressure when the command signal is changed under reference conditions after the calibration conditions have been met. Once the first actual signal I11 is derived, the process proceeds to step S15.

[0040] In step S15, which is the second actual signal derivation process, the control device 16 changes the command signal from the second reference signal I20 under reference conditions (see arrow Y2 in Figure 6, for example). As a result, the discharge pressure of the hydraulic pump 11 changes. By changing the discharge pressure, the control device 16 derives the second actual signal I21, which is the signal when the discharge pressure detected by the pressure sensor 15 becomes the second reference pressure pd2 (see second actual signal I21 in Figure 6). Once the second actual signal I21 is derived, the process proceeds to step S16.

[0041] In step S16, which is a calibration process, the pump characteristics are calibrated based on the first real signal I11 and the second real signal I21. More specifically, the pump characteristics of the hydraulic pump 11 are basically represented by a linear function (see the pump characteristics before calibration conditions are met, shown by the solid line in Figure 7). Therefore, the pump characteristics can be determined once the discharge capacity of the controlled hydraulic pump 11 is derived for each of the two command signals. In the pump calibration system 1A, regardless of whether the command signal is the first reference signal I10 or the first real signal I11, the first reference pressure pd1 is measured as the discharge pressure under the reference environment. Therefore, in either case, the discharge capacity of the hydraulic pump 11 is the first reference discharge capacity q1 (first reference value). Similarly, when the command signal is the second reference signal I20 and the second real signal I21, the discharge capacity of the hydraulic pump 11 is the second reference discharge capacity q2 (second reference value). Therefore, after the calibration conditions are met, the discharge capacity of the hydraulic pump 11 becomes the first reference discharge capacity q1 when the command signal is the first actual signal I11, and the second reference discharge capacity q2 when the command signal is the second actual signal I21. Therefore, the control device 16 can calibrate the pump characteristics to a function (see the two-bar in Figure 7) in which the discharge capacity when the command signal is the first actual signal I11 is the first reference discharge capacity q1 and the discharge capacity when the command signal is the second actual signal I21 is the second reference discharge capacity q2. Once the pump characteristics are calibrated in this way, the pump calibration method is completed.

[0042] In the pump calibration system 1A of this embodiment, the pump characteristics are calibrated based on a second actual signal I21 and a first actual signal I11, which have the same discharge pressure as the discharge pressure detected when the second reference signal I20 is output. Therefore, the pump characteristics can be calibrated based on two signal values ​​without converting pressure to flow rate. As a result, since the pump characteristics are calibrated based on two signal values, the pump characteristics can be calibrated accurately and easily.

[0043] Furthermore, in the pump calibration system 1A of this embodiment, the pump characteristics are calibrated to a function in which the discharge capacity when the command signal is the first actual signal I11 is the first reference discharge capacity q1, and the discharge capacity when the command signal is the second actual signal I21 is the second reference discharge capacity q2. Therefore, the function can be easily calculated, and the pump characteristics can be calibrated more precisely.

[0044] Furthermore, the pump calibration system 1A of the second embodiment provides the same effects and advantages as the pump calibration system 1 of the first embodiment. The pump calibration method of the second embodiment also provides the same effects and advantages as the discharge capacity calibration of the first embodiment.

[0045] <Other Embodiments> In the pump calibration system 1,1A of this embodiment, the regulator 12 is composed of a servo piston 12a and an electromagnetic proportional valve 12b, but is not limited to such a configuration. For example, the servo piston 12a may be driven by a linear motor or the like. In that case, the discharge capacity is changed by inputting a command signal to the linear motor. Also, the unload valve 14 may be a two-position spool valve that does not have a first position A1. In this case, the position of the spool 14a of the unload valve 14 is controlled so that the opening degree is fixed to a predetermined value at the position corresponding to the third position. As a result, even with a two-position spool valve, the pump characteristics are calibrated in the same way as described above. Furthermore, the control device 16 may be configured with a part that controls the regulator 12 and a part that calibrates the pump characteristics in separate components.

[0046] Furthermore, in the pump calibration method of this embodiment, the pump characteristics are calibrated at any timing by selecting a mode by an operator, but the pump characteristics may also be configured periodically. That is, the pump characteristics are calibrated periodically by setting the calibration condition to after a predetermined time has elapsed. In addition, the control device 16 may periodically measure a command signal that becomes the first reference pressure pd under reference conditions, and the pump characteristics may be calibrated when the command signal differs from the first reference signal I0. Moreover, the number of reference signals and actual signals measured to calibrate the pump characteristics does not necessarily have to be one, as in the first embodiment, or two, as in the second embodiment. For example, the number of reference signals and actual signals may be three or more, and in the case of three or more, the pump characteristics may be derived using a linear approximation method such as the least squares method.

[0047] In the pump calibration method of this embodiment, the pump characteristics represent the relationship between the command signal and the discharge capacity of the hydraulic pump 11, but they may also represent the relationship between the command signal and the discharge flow rate of the hydraulic pump 11. In this case as well, the pump characteristics can be calibrated in the same manner as the pump calibration method described above.

[0048] <Exemplary Embodiment> The pump calibration system in the first phase comprises a variable displacement hydraulic pump capable of changing the discharge capacity, a regulator that changes the discharge capacity of the hydraulic pump according to an input command signal, an unload valve positioned between the hydraulic pump and a tank and whose opening degree can be changed, a pressure sensor that measures the discharge pressure of the hydraulic pump, and a control device that controls the discharge capacity of the hydraulic pump by outputting a command signal to the regulator and calibrates the pump characteristics that show the relationship between the command signal and the discharge capacity or discharge flow rate of the hydraulic pump. The control device stores in advance the pressure detected by the pressure sensor as the first reference pressure when a predetermined first reference signal is output to the regulator under measurement conditions in which the opening degree of the unload valve is fixed to a predetermined value and the hydraulic pump is driven to rotate at a predetermined rotational speed, and when predetermined calibration conditions are met, it changes the command signal output to the regulator in order to make the discharge pressure detected by the pressure sensor under the measurement conditions the first reference pressure, and calibrates the pump characteristics based on the first actual signal, which is the command signal when the discharge pressure becomes the first reference pressure.

[0049] According to the above scenario, the pump characteristics can be calibrated based on the stored pump characteristics. The pump characteristics are calibrated based on the first actual signal, which has the same discharge pressure as the discharge pressure detected when the first reference signal is output. Therefore, the pump characteristics can be easily calibrated without using a flow meter.

[0050] In the pump calibration system in the second phase, the pump characteristics in the pump calibration system in the first phase indicate the relationship between the input command signal and the discharge capacity or discharge flow rate that the regulator should control, and the control device calibrates the pump characteristics according to the difference between the first actual signal and the first reference signal.

[0051] According to the above scenario, the pump characteristics are calibrated to adjust the command signal according to the difference between the first real signal and the first reference signal. Therefore, the pump characteristics can be calibrated more easily.

[0052] In the pump calibration system in the third phase, in the pump calibration system in the first or second phase, the control device pre-stores the pressure detected by the pressure sensor as the second reference pressure when a predetermined second reference signal is output to the regulator under the measurement conditions, and then changes the command signal output to the regulator to make the discharge pressure detected by the pressure sensor under the measurement conditions the second reference pressure, and calibrates the pump characteristics based on the second actual signal, which is the command signal when the discharge pressure becomes the second reference pressure, and the first actual signal.

[0053] According to the above scenario, the pump characteristics are calibrated based on the first and second actual signals, which have the same discharge pressure as the discharge pressure detected when the second reference signal is output. Therefore, the pump characteristics can be calibrated based on two signals without using a flow meter. Consequently, the pump characteristics can be calibrated with high accuracy.

[0054] In the fourth phase of the pump calibration system, in the third phase of the pump calibration system, the pump characteristics are a function that indicates the discharge capacity or discharge flow rate that the regulator should control in response to the input command signal, and the control device calibrates the pump characteristics to a function in which the discharge capacity or discharge flow rate when the command signal is a first real signal is a first reference value, and the discharge capacity or discharge flow rate when the command signal is a second real signal is a second reference value.

[0055] According to the above scenario, the pump characteristics are calibrated to a function where the discharge capacity or discharge flow rate when the command signal is the first actual signal is the first reference value, and the discharge capacity or discharge flow rate when the command signal is the second actual signal is the second reference value. Therefore, the function can be easily calculated, and the pump characteristics can be calibrated more precisely.

[0056] In the fifth phase of the pump calibration system, in any of the first to fourth phases of the pump calibration system, the unload valve has a valve body that can move to a first position in which the opening degree is fixed to a predetermined value, a second position in which the hydraulic pump and the tank are blocked, and a third position in which the opening degree is changed according to the stroke amount, and the control device moves the valve body of the unload valve to the first position under the measurement conditions.

[0057] According to the above scenario, the control device moves the valve body of the unload valve to a first position where the opening degree is fixed at a predetermined value under the measurement conditions. Therefore, it is easy to maintain the opening degree at the predetermined value. This makes it easy to maintain the valve under measurement conditions in order to detect the discharge pressure.

[0058] The pump calibration method in the sixth phase is a pump calibration method for calibrating pump characteristics that show the relationship between a command signal input to a regulator when the regulator changes the discharge capacity of a variable displacement hydraulic pump and the discharge capacity or discharge flow rate, comprising: a first reference pressure detection step of storing a first reference pressure detected by a pressure sensor when the regulator changes the discharge capacity of the hydraulic pump in response to a first reference signal input under predetermined measurement conditions in which the opening degree of an unload valve arranged between the hydraulic pump and a tank is fixed to a predetermined value; a first actual signal derivation step of changing the command signal output to the regulator under the measurement conditions and deriving a first actual signal which is a command signal when the discharge pressure becomes the first reference pressure; and a calibration step of calibrating the pump characteristics based on the first actual signal, wherein in the first reference pressure detection step, the first reference pressure is detected before the predetermined calibration conditions are satisfied, and in the first actual signal derivation step, the command signal output to the regulator is changed after the calibration conditions are satisfied and the first actual signal is derived.

[0059] According to the above scenario, the first reference pressure is detected before the calibration conditions are met, and after the calibration conditions are met, the signal output to the regulator is changed to make the discharge pressure equal to the first reference pressure, thereby producing the first actual signal. Therefore, the pump characteristics after the calibration conditions are met can be calibrated using the pump characteristics before the calibration conditions are met as a reference. As a result, the pump characteristics are calibrated based on the first actual signal, which has the same discharge pressure as the discharge pressure detected when the first reference signal is output. Therefore, the pump characteristics can be easily calibrated without using a flow meter. [Explanation of Symbols]

[0060] 1.1A Pump Calibration System 11. Hydraulic pump 12 Regulators 14 Unload valve 14a Spool (valve body) 15. Pressure Sensor 16 Control device 20 tanks

Claims

1. A variable displacement hydraulic pump that can change the discharge volume, A regulator that changes the discharge capacity of the hydraulic pump in response to an input command signal, An unload valve, which is positioned between the hydraulic pump and the tank and whose opening degree can be changed, A pressure sensor for measuring the discharge pressure of the aforementioned hydraulic pump, The control device comprises a control device that controls the discharge capacity of the hydraulic pump by outputting a command signal to the regulator, and calibrates the pump characteristics that show the relationship between the command signal and the discharge capacity or discharge flow rate of the hydraulic pump, The control device has an initial state storage mode and a calibration mode. In the initial state memory mode, the control device stores in advance the pressure detected by the pressure sensor as the first reference pressure when it outputs a predetermined first reference signal to the regulator under measurement conditions in which the opening degree of the unload valve is fixed to a predetermined value and the hydraulic pump is driven to rotate at a predetermined rotational speed. In the calibration mode, the control device changes the command signal output to the regulator under the measurement conditions to set the discharge pressure detected by the pressure sensor as a first reference pressure, and calibrates the pump characteristics based on the difference between the first actual signal, which is the command signal when the detected discharge pressure becomes the first reference pressure, and the first reference signal, in a pump calibration system.

2. The pump calibration system according to claim 1, wherein the pump characteristics indicate the relationship between the input command signal and the discharge capacity or discharge flow rate that the regulator should control.

3. A variable displacement hydraulic pump capable of changing the discharge volume, A regulator that changes the discharge capacity of the hydraulic pump in response to an input command signal, An unload valve, which is positioned between the hydraulic pump and the tank and whose opening degree can be changed, A pressure sensor for measuring the discharge pressure of the aforementioned hydraulic pump, The control device controls the discharge capacity of the hydraulic pump by outputting a command signal to the regulator, and calibrates the pump characteristics that show the relationship between the command signal and the discharge capacity or discharge flow rate of the hydraulic pump. The control device has an initial state storage mode and a calibration mode. In the initial state memory mode, the control device pre-stores the pressure detected by the pressure sensor as the first reference pressure when a predetermined first reference signal is output to the regulator under measurement conditions in which the opening degree of the unload valve is fixed to a predetermined value and the hydraulic pump is driven to rotate at a predetermined rotational speed, and pre-stores the pressure detected by the pressure sensor as the second reference pressure when a predetermined second reference signal is output to the regulator under the same measurement conditions. Pump calibration system in the calibration mode, wherein the control device changes the command signal output to the regulator under the measurement conditions to set the discharge pressure detected by the pressure sensor as a first reference pressure, sets the command signal when the detected discharge pressure becomes the first reference pressure as a first actual signal, and changes the command signal output to the regulator under the measurement conditions to set the discharge pressure detected by the pressure sensor as a second reference pressure, and calibrates the pump characteristics based on the difference between the second actual signal, which is the command signal when the detected discharge pressure becomes the second reference pressure, and the first actual signal.

4. The pump characteristics are a function that indicates the discharge capacity or discharge flow rate that the regulator should control in response to the input command signal. The pump calibration system according to claim 3, wherein the control device calibrates the pump characteristics to a function in which the discharge capacity or discharge flow rate when the command signal is a first actual signal is a first reference value, and the discharge capacity or discharge flow rate when the command signal is a second actual signal is a second reference value.

5. The unload valve has a valve body that can move to a first position in which the opening degree is fixed at a predetermined value, a second position in which the connection between the hydraulic pump and the tank is blocked, and a third position in which the opening degree is changed according to the stroke amount. The pump calibration system according to claim 1, wherein the control device moves the valve body of the unload valve to a first position under the measurement conditions.

6. A pump calibration method for calibrating the pump characteristics, which show the relationship between the command signal input to a regulator and the discharge capacity or discharge flow rate when the regulator changes the discharge capacity of a variable displacement hydraulic pump, A first reference pressure detection step, which stores a first reference pressure detected by a pressure sensor when the regulator changes the discharge capacity of the hydraulic pump in response to a first reference signal input under predetermined measurement conditions in which the opening degree of the unload valve, which is located between the hydraulic pump and the tank, is fixed to a predetermined value; A first actual signal derivation step involves changing the command signal output to the regulator under the aforementioned measurement conditions and deriving a first actual signal, which is the command signal when the detected discharge pressure becomes a first reference pressure. The system includes a calibration step of calibrating the pump characteristics based on the difference between a first actual signal and a first reference signal. In the first reference pressure detection step, the first reference pressure is detected before the predetermined calibration conditions are met. A pump calibration method in which, in the first actual signal derivation step, the command signal output to the regulator after the calibration conditions are satisfied is changed to derive the first actual signal.

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