Control Calibration Apparatus for Variable-Capacity Pump and Method Thereof

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 variable-capacity 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.

Patent Document 1: JP 2008-303813A

Patent Document 2: JP 2014-177969A

Patent Document 3: JP 2019-190443A

Patent Literature 4: Republished Patent No. 2019/106831

Patent Document 5: JP 2020-128733A

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 variable-capacity 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.

The invention according to claimis 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 claimis 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 claimis 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 claimis 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 claimoris 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 claimis 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 variable-capacity 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 claimis a control calibration method of a variable-capacity pump, wherein in the control calibration method of the variable-capacity pump according to claim, 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 claimis a control calibration method of a variable-capacity pump, wherein in the control calibration method of the variable-capacity pump according to claimor, the flow rate of the variable-capacity pump is measured based on a discharge pressure.

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

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

According to the invention described in claim, 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, 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.

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

illustrates a part of the hydraulic circuitthat is, for example, a fluid pressure control circuit mounted on a working machine. In this working machine, a variable-capacity pump(hereinafter referred to as the pump), which is a fluid pressure pump driven by the vehicle-mounted engine, supplies hydraulic oil of the working fluid in the tankto a plurality of spool valves which are integratedly provided in a block as a control valve connected to a pump discharge passage, 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, various spool valves are operated in accordance with an operating amount of the operating device, such as a lever or a pedal. A signal corresponding to the operating amount of the operating deviceis input to an input side of the controller, and the discharge amount of the hydraulic oil by the pumpis controlled in accordance with a value of current of a command signal for a flow rate command output from the controllerbased on the input signal.

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

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

Here, it is ideal for the pumpto 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, and the actual deviation from the ideal operation is large.

Accordingly, in the present embodiment, the controllerhas a calibration mode for calibrating (setting) the control table, or in other words, the control of the pump, based on the measured values for each pump, 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 controllerand a flow sensorthat detects the discharge flow rate of the pump. Preferably, the flow sensoruses a pressure sensor that detects the discharge pressure of the pump. In other words, the flow sensoris a flow measurement pressure sensor that measures the flow rate based on a fixed predetermined throttling condition of the hydraulic circuitor a fixed predetermined engine speed or a pump rpm in which the discharge flow rate of the pumpis linked to the discharge pressure. The flow sensoris connected to the pump discharge passageand its output signal is connected to the input side of the controller. Note that in the present embodiment, the flow rate sensoris installed as a standard in the hydraulic circuitfor 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 pumpwill be described.

By setting the calibration mode in the controllerby operating a predetermined input means such as an in-vehicle monitor, the controllerexecutes a calibration program.

As a summary, first, as shown in, in a circuit for executing a calibration program in which the pump discharge passageis directly connected to the tankvia an orifice (aperture), the controllermonitors the discharge pressure of the pumpby the flow sensorwhile increasing the value of current for the flow rate command relative to the pump, and stores the value of current when the discharge pressure of the flow sensoris saturated (saturated) as the first value of current Imax corresponding to the maximum flow rate Qmax. Similarly, the controllermonitors the discharge pressure of the pumpby the flow rate sensorwhile decreasing the value of current for the flow rate command relative to the pump, and stores the value of current when the discharge pressure of the flow rate sensoris saturated (saturated) as a second value of current Imin corresponding to the minimum flow rate Qmin. Further, according to the specification of the pump, a fixed value of current Qmid corresponding to the fixed flow rate Qmid is input or stored in advance in the controlleras 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, which are detected and provided for each pumpby an outgoing inspection performed by the manufacturer of the pumpalone, respectively. Then, as shown in, 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 P1 (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, these sequences of processes are automatically performed.

Operations in the calibration mode will be described in detail with reference toto().

First, in step S, the controllerforms a circuit for executing the calibration program that directly connects the pump discharge passagewith the tankvia the orificestandardly installed in the hydraulic circuitby outputting a command signal to a valve or the like installed in the hydraulic circuit(()).

Then, in step S, the controllerincreases 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, or may be increased stepwise by a predetermined current width.

In step S, the flow rate is monitored by detecting the discharge pressure P of the pump() using the flow rate sensor.

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

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

Then, in step S, the controllerreduces 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, or may be decreased stepwise by a predetermined current width.

In step S, the flow rate is monitored by detecting the discharge pressure P of the pump() using the flow rate sensor.

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

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

Note that the steps Sto Sand the steps Sto Smay be reversed in order.

Furthermore, in step S, from the first value of current Imax when the maximum flow rate Qmax of the pumpis measured, the second value of current Imin when the minimum flow rate Qmin of the pumpis measured, and the fixed value of current Imid corresponding to the fixed flow rate Qmid based on the specifications of the pumpstored or input in advance, a quadratic function formula f for flow control of the pumpis 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 (x1, y1), (x2, y2), and (x3, y3) on the coordinate plane is y=ax2+bx+c (where a, b, and c are real numbers, respectively), a, b, and c are each determined by the following formulas: