CONTROL CALIBRATION APPARATUS FOR VARIABLE-CAPACITY PUMP AND METHOD THEREOF

Field of the Disclosure

The present invention relates to a control calibration apparatus for a variable-capacity pump that sets a current-to-flow characteristic for flow control of a current-controlled variable-capacity pump and a method thereof.

Although the current-controlled variable-capacity pump used in a work machine or the like is ideal for changing the flow rate linearly relative to the current in terms of current-to-flow characteristics, in practice, variations in manufacturing and hysteresis between the rise and fall of the value of current for the flow rate command occur, and there is a large deviation in the actual state from the ideal operation. Accordingly, it is known that the current-to-flow characteristics are calibrated according to the variable-capacity pump (see, e.g., Patent Documents 1 to 5).

Patent Literature 1 describes that by changing the value of current for the flow rate command while monitoring the pressure of the action on the actuator piston, the value of current at the actual minimum or maximum swashplate position corresponding to the change point of the captured pressure value is obtained, and a difference between the obtained value of current and the value of current on the preset specification as a correction value is added to a target value of current. Patent Document 2 describes that a command value of current of a variablecapacity pump is changed from the minimum to the maximum, and the command value of current when a pump discharge pressure starts to increase from a minimum reference value and the command value of current when a maximum reference value is reached are actually measured, and the command value of current of the variable-capacity pump is changed from the maximum to the minimum, and the command value of current when the pump discharge pressure starts to decrease from the maximum reference value and the command value of current when the minimum reference value is reached are actually measured, and then the current- to-flow characteristics are calibrated using the detected command value of current.

Patent Literature 3 describes using an oil path of a stick unload valve to actually measure a pump pressure while changing the command value of current to the maximum capacity of the pump in multiple stages while suppressing the rise in pump pressure, and obtaining a relationship between the control current from the pump pressure actually measured and the pump capacity.

Patent Document 4 describes setting an adjustment line connecting an actual command value of current at a maximum flow rate of a variable-capacity pump and an actual command value of current at a minimum flow rate, and using the adjustment line to suppress the deviation of hysteresis characteristics.

Patent Literature 5 describes actually measuring two calibration points of command value of currents at a flow rate between the maximum flow rate and the minimum flow rate, and setting a straight line connecting those calibration points as a new reference characteristic.

Prior Art Documents

Patent Document Patent Document 1 : JP 2008-303813A

Patent Document 2: JP 2014- 177969 A

Patent Document 3: JP 2019- 190443 A

Patent Literature 4: Republished Patent No. 2019/106831

Patent Document 5: JP 2020-128733 A

Summary of the Invention

Problems to be Solved by the Invention

In the case of the invention described in Patent Documents 1 and 2, there is problem about the accuracy of the calibration because the calibration value is calculated based on the change point of the pressure at which the change point is difficult to find. In addition, in the case of the invention described in Patent Documents 3 to 5, the calibration properties are set by a straight line, however there is a problem in the accuracy of the calibration, especially in the case of a variablecapacity pump having non-linear properties.

An object of the present invention aims to provide a control calibration apparatus for a variable-capacity pump capable of improving the flow control accuracy of a variable-capacity pump and a method thereof.

Means for Solving the Problem

The invention according to claim 1 is a control calibration apparatus of a variable-capacity pump for setting a current-to-flow characteristic for flow control of current-controlled variable-capacity pump, wherein the control calibration apparatus comprises a controller for outputting a value of current of a flow rate command of the variable-capacity pump and a flow sensor for measuring a flow rate of the variable-capacity pump, wherein the controller has a function for obtaining a quadratic function formula that is a current-to-flow characteristic of the variable-capacity pump for flow control from a first value of current when a maximum flow rate of the variable-capacity pump is measured by the flow sensor, a second value of current when a minimum flow rate of the variable-capacity pump is measured by the flow sensor, and a fixed value of current corresponding to a fixed flow rate based on the specifications of the variable-capacity pump.

The invention according to claim 2 is a control calibration apparatus of the variable-capacity pump, wherein the first value of current in the control calibration apparatus of the variable-capacity pump according to claim l is a value of current when the flow rate sensor measures saturation of the flow rate at a time of the value of current for the flow rate command of the variable-capacity pump increasing, and the second value of current is a value of current when the flow rate sensor measures saturation of the flow rate at a time of the value of current for the flow rate command of the variable-capacity pump falling.

The invention according to claim 3 is a control calibration apparatus of a variable-capacity pump, wherein the flow rate sensor in the control calibration apparatus of the variable-capacity pump according to claim 1 or 2 is a flow measurement pressure sensor of the variable-capacity pump, which measures the flow rate based on the discharge flow rate of the variable-capacity pump in relation to a discharge pressure under a fixed throttle condition or a fixed rotational speed condition.

The invention according to claim 4 is a control calibration method of a variable-capacity pump that sets a current-to-flow characteristic for flow control of a current-controlled variable-capacity pump, including obtaining a quadratic function formula from a first value of current for a flow rate command when a maximum flow rate of the variable-capacity pump is measured, a second value of current for a flow rate command when a minimum flow rate of the variablecapacity pump is measured, and a fixed value of current corresponding to a fixed flow rate based on a specification of the variable-capacity pump.

The invention according to claim 5 is a control calibration method of a variable-capacity pump, wherein in the control calibration method of the variablecapacity pump according to claim 4, the first value of current is a value of current when saturation of the flow rate is measured at a time of the value of current for the flow rate command of the variable-capacity pump increasing, and the second value of current is a value of current when the saturation of the flow rate is measured at a time of the value of current for the flow rate command of the variable-capacity pump falling.

The invention according to claim 6 is a control calibration method of a variable-capacity pump, wherein in the control calibration method of the variablecapacity pump according to claim 4 or 5, the flow rate of the variable-capacity pump is measured based on a discharge pressure.

Effect of the Invention

According to the invention described in claim 1, the current-to-flow characteristics can be brought closer to the actual characteristics of the variablecapacity pump to improve the flow control accuracy of the variable-capacity pump.

According to the invention described in claim 2, in a variable-capacity pump having a hysteresis in the current-to-flow characteristic when the value of current increases and falls, the first value of current and the second value of current for obtaining the quadratic function formula can be accurately obtained. According to the invention described in claim 3, the calibration can be carried out by using a pressure sensor mounted in advance without installing a dedicated calibration instrument or sensor separately.

According to the invention described in claim 4, the current-to-flow characteristics can be brought closer to the actual characteristics of the variablecapacity pump to improve the flow control accuracy of the variable-capacity pump.

According to the invention described in claim 5, in a variable capacitive pump having a hysteresis in the current-to-flow characteristic when the value of current rises and falls, the first value of current and the second value of current for obtaining the quadratic function formula can be accurately obtained.

According to the invention described in claim 6, the calibration can be carried out by using a pressure sensor mounted in advance, without installing a dedicated calibration instrument or a pressure sensor separately. of the Drawings

FIG. 1 (a) is a circuit diagram illustrating an embodiment of a control calibration apparatus of a variable-capacity pump according to the present invention, and (b) is a circuit diagram for monitoring a flow rate in a calibration mode.

FIG. 2 is a graph showing current-to-flow characteristics of a variablecapacity pump controlled by the same control calibration apparatus of a variablecapacity pump.

FIG. 3 (a) is a flowchart showing a calibration program of the control calibration apparatus of the same variable-capacity pump, (b) is a graph showing the changes in the value of current in the calibration program of the same control calibration apparatus of a variable-capacity pump, and (c) is a graph showing the changes in the detection pressure at the flow sensor according to (b).

Detailed Description of Best Mode Carrying Out the Invention

Embodiments of the present invention will be described below with reference to the drawings.

Figure 1 (a) illustrates a part of the hydraulic circuit 1 that is, for example, a fluid pressure control circuit mounted on a working machine. In this working machine, a variable-capacity pump 3 (hereinafter referred to as the pump 3), which is a fluid pressure pump driven by the vehicle-mounted engine 2, supplies hydraulic oil of the working fluid in the tank 4 to a plurality of spool valves which are integratedly provided in a block as a control valve connected to a pump discharge passage 5, performs direction control and flow control on the hydraulic oil according to the displacement direction and displacement amount of the spool valves, and supplies the hydraulic oil to a plurality of fluid pressure actuators such as a hydraulic motor and a hydraulic cylinder, respectively.

In such a hydraulic circuit 1, various spool valves are operated in accordance with an operating amount of the operating device 6, such as a lever or a pedal. A signal corresponding to the operating amount of the operating device 6 is input to an input side of the controller 10, and the discharge amount of the hydraulic oil by the pump 3 is controlled in accordance with a value of current of a command signal for a flow rate command output from the controller 10 based on the input signal.

In other words, the pump 3 is a current-controlled type, and the capacity variable means such as a swashplate are controlled by a regulator 3a operated by a solenoid valve (electromagnetic proportional valve) that receives a command signal output from the controller 10, so that the capacity variable means can be adjusted according to the load from the minimum flow rate at no load.

The controller 10 controls the swashplate tilt angle of the pump 3 by activating the regulator 3 a via the solenoid valve by means of a command signal corresponding to the target flow rate of the pump 3. Accordingly, the controller 10 has a control table (current-to-flow characteristic (IQ characteristic)) that controls a relationship between the target flow rate of the pump 3 and the value of current on the preset specification (the SPEC), and in the normal control mode, the flow rate of the pump 3 is controlled based on the control table according to the value of current of the command signal output from the controller 10 .

Here, it is ideal for the pump 3 to linearly increase or decrease the flow rate with respect to the increase or decrease of the value of current in terms of the current-to-flow characteristics, but in practice, due to the manufacturing errors, hysteresis occurs between the rise and fall of the value of current for the flow rate command, as indicated by the arrows in FIG. 2, and the actual deviation from the ideal operation is large.

Accordingly, in the present embodiment, the controller 10 has a calibration mode for calibrating (setting) the control table, or in other words, the control of the pump 3, based on the measured values for each pump 3, in order to ensure the control accuracy during the actual operation. Normally, the calibration mode is executed by activating the mode when leaves the factory.

In order to perform calibration in the calibration mode, the present embodiment uses a controller 10 and a flow sensor 11 that detects the discharge flow rate of the pump 3. Preferably, the flow sensor 11 uses a pressure sensor that detects the discharge pressure of the pump 3. In other words, the flow sensor 11 is a flow measurement pressure sensor that measures the flow rate based on a fixed predetermined throttling condition of the hydraulic circuit 1 or a fixed predetermined engine speed or a pump rpm in which the discharge flow rate of the pump 3 is linked to the discharge pressure. The flow sensor 11 is connected to the pump discharge passage 5 and its output signal is connected to the input side of the controller 10. Note that in the present embodiment, the flow rate sensor 11 is installed as a standard in the hydraulic circuit 1 for detecting the hydraulic power or the hydraulic load for controlling the control valve for normal control, and it is not specifically for the calibration mode.

Next, a control calibration method of the pump 3 will be described.

By setting the calibration mode in the controller 10 by operating a predetermined input means such as an in-vehicle monitor, the controller 10 executes a calibration program.

As a summary, first, as shown in FIG. 1 (b), in a circuit for executing a calibration program in which the pump discharge passage 5 is directly connected to the tank 4 via an orifice (aperture) 15, the controller 10 monitors the discharge pressure of the pump 3 by the flow sensor 11 while increasing the value of current for the flow rate command relative to the pump 3, and stores the value of current when the discharge pressure of the flow sensor 11 is saturated (saturated) as the first value of current Imax corresponding to the maximum flow rate Qmax. Similarly, the controller 10 monitors the discharge pressure of the pump 3 by the flow rate sensor 11 while decreasing the value of current for the flow rate command relative to the pump 3, and stores the value of current when the discharge pressure of the flow rate sensor 11 is saturated (saturated) as a second value of current Imin corresponding to the minimum flow rate Qmin. Further, according to the specification of the pump 3, a fixed value of current Qmid corresponding to the fixed flow rate Qmid is input or stored in advance in the controller 10 as an intermediate point between a first value of current Imax corresponding to the maximum flow rate Qmax and a second value of current Imin corresponding to the minimum flow rate Qmin. That is, in the present embodiment, the fixed flow rate Qmid is a flow rate (Qmin < Qmid < Qmax) that is greater than the minimum flow rate Qmin and less than the maximum flow rate Qmax. The maximum flow rate Qmax, the minimum flow rate Qmin, the fixed flow rate Qmid and the fixed value of current Imid are known values based on the specifications of pump 3, which are detected and provided for each pump 3 by an outgoing inspection performed by the manufacturer of the pump 3 alone, respectively. Then, as shown in FIG. 2, on a coordinate plane in which the value of current is on the x-axis (horizontal axis) and the flow rate is on the y-axis (vertical axis), a quadratic function formula f (mathematically, the quadratic function formula f passing through three points is uniquely determined) can be obtained through three points: point Pl (Imax, Qmax), point P2 (Imin, Qmin), and point P3 (Imid, Qmid), and the quadratic function formula f is stored (set) in a non-volatile memory as a control table. By executing the calibration program at the controller 10, these sequences of processes are automatically performed.

Operations in the calibration mode will be described in detail with reference to FIGS. 3 (a) to 3 (c).

First, in step SI, the controller 10 forms a circuit for executing the calibration program that directly connects the pump discharge passage 5 with the tank 4 via the orifice 15 standardly installed in the hydraulic circuit 1 by outputting a command signal to a valve or the like installed in the hydraulic circuit 1 (FIG. 1 (b))- Then, in step S2, the controller 10 increases the value of current I for the flow rate command from a small value of current such as 0. The increase in value of current I may be increased sequentially (linearly) as shown in FIG. 3 (b), or may be increased stepwise by a predetermined current width.

In step S3, the flow rate is monitored by detecting the discharge pressure P of the pump 3 (FIG. 3 (c)) using the flow rate sensor 11.

Then, in step S4, it is determined whether or not the discharge pressure P has increased.

In the case where it is determined in step S4 that the discharge pressure P has increased, the process returns to step S2, and in the case where it is determined in step S4 that the discharge pressure P has not increased, it is determined that the flow rate of the pump 3 has reached the maximum flow rate Qmax stored or input in advance for each pump 3, and in step S5, the value of current at that time is stored as the first value of current Imax.

Then, in step S6, the controller 10 reduces the value of current I for the flow rate command. The reduction of the value of current I may be decreased sequentially (linearly) as shown in FIG. 3 (b), or may be decreased stepwise by a predetermined current width.

In step S7, the flow rate is monitored by detecting the discharge pressure P of the pump 3 (FIG. 3 (c)) using the flow rate sensor 11.

Then, in step S8, it is determined whether or not the discharge pressure P has decreased.

In the case where it is determined in step S8 that the discharge pressure P has decreased, the process returns to step S6, and in the case where it is determined in step S8 that the discharge pressure P has not decreased, it is determined that the flow rate of the pump 3 has reached the minimum flow rate Qmin stored or input in advance for each pump 3, and in step S9, the value of current at that time is stored as the second value of current Imin.

Note that the steps S2 to S5 and the steps S6 to S9 may be reversed in order.

Furthermore, in step S10, from the first value of current Imax when the maximum flow rate Qmax of the pump 3 is measured, the second value of current Imin when the minimum flow rate Qmin of the pump 3 is measured, and the fixed value of current Imid corresponding to the fixed flow rate Qmid based on the specifications of the pump 3 stored or input in advance, a quadratic function formula f for flow control of the pump 3 is obtained in a coordinate plane where the value of current is taken as the x-axis and the flow rate is taken as the y-axis.

Here, when the quadratic function formula f passing through the three points (xl, yl), (x2, y2), and (x3, y3) on the coordinate plane is y = ax ² + bx + c (where a, b, and c are real numbers, respectively), a, b, and c are each determined by the following formulas: a = {(yl-y2) • (xl-x3) - (yl-y3) • (xl-x2)}/{(xl-x2) • (xl-x3) • (x2-x3)} b = (yl-y2)/(xl-x2) -a • (xl + x2) c = yl-a • xl ² -b • xl

Therefore, by substituting the value of currents Imax, Imin, and Imid in xl, x2, and x3 of the above formulas, and substituting the flow rates Qmax, Qmin, and Qmid in yl, y2, and y3, respectively, a specific quadratic function formula f can be obtained. Then, in step S 11, the quadratic function formula f obtained in step S10 is stored in the non-volatile memory as a characteristic table, and the calibration program is terminated. Note that if a characteristic table or the like based on the standard specifications of the pump 3 is stored in the non-volatile memory in advance, it may be corrected or may be newly stored.

Then, in the normal control mode, the controller 10 outputs a command signal that controls the flow rate of the pump 3 based on the characteristic table stored in step S 11.

As described above, according to the aforementioned embodiment, the current-to-flow characteristics of the pump 3 can be brought closer to the actual characteristics of the pump 3 by obtaining, from the first value of current for the flow rate command when the maximum flow rate of the pump 3 is measured, the second value of current for the flow rate command when the minimum flow rate of the pump 3 is measured, and the fixed value of current corresponding to the fixed flow rate based on the specifications of the pump 3, a quadratic function formula that serves as a current-to-flow characteristic for the flow rate control of the pump 3, thereby improving the flow control accuracy of the pump 3.

Moreover, since only two points of data are obtained by actual measurement, it is not necessary to actually measure a large number of points, so it is possible to calibrate in a short time without complicated calculations.

By taking the value of current when the saturation of the flow rate is measured when the value of current for the flow rate command of the pump 3 rises as the first value of current, and taking the value of current when the saturation of the flow rate is measured when the value of current for the flow rate command of the pump 3 falls as the second value of current, the first value of current and the second value of current for obtaining the quadratic function formula can be accurately obtained in the pump 3 having a hysteresis in the current-to-flow characteristic when the value of current rises and falls.

By measuring the flow rate of the pump 3 based on the fact that the discharge flow rate of the pump 3 is linked to the discharge pressure under a fixed aperture condition or a fixed engine rpm condition, the pressure sensor installed in the hydraulic circuit 1 in advance can be used as the flow sensor 11 to perform calibration without installing a dedicated calibration instrument or sensor separately. Note that in the aforementioned embodiment, the accuracy of the quadratic function formula may be further improved by obtaining the first value of current and the second value of current (steps S2 to S9 in FIG. 3 (a)) multiple times, and finding the quadratic function formula using representative values such as the average value and the most frequent value. Industrial Applicability

The present invention has industrial potential for a business operator engaged in manufacturing, selling, or the like of a working machine such as a hydraulic excavator equipped with a variable-capacity pump.