JP2009007975A - Inverter drive control method for hydraulic pump - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To prevent the self-exciting vibration of a variable displacement piston pump during inverter drive. <P>SOLUTION: A rotating speed to be commanded to an inverter device 30 is calculated in accordance with the detected pressure of a control piston 17 in a pressure chamber 18. When the calculated rotating speed is higher than a currently commanded rotating speed by a certain value d or greater, a value that the certain value d is subtracted from the calculated value is set as the rotating speed to be commanded to the inverter device 30. When the calculated rotating speed is lower than the currently commanded rotating speed by the certain value d or greater, a value that the certain value d is added to the calculated value is set as the rotating speed to be commanded to the inverter device 30. When an absolute value for a difference between the calculated rotating speed and the currently commanded rotating speed is the certain value d or smaller, backlash operation is performed not to change the value for the rotating speed to be commanded to the inverter device 30, and it is set as the rotating speed to be commanded to the inverter device 30. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an inverter drive control method for a hydraulic pump, and more particularly to an inverter drive control method for a hydraulic pump that reduces power consumption by lowering the rotational speed of the hydraulic pump.

Conventionally, as an inverter drive control method of this type of variable displacement pump, as shown in Patent Document 1, a hydraulic pump, a variable speed motor that drives the hydraulic pump, an inverter device that drives the variable speed motor, A control device for giving a rotation speed command to the inverter device and a pressure sensor are provided, and when the discharge pressure exceeds a preset pressure, power consumption is reduced by reducing the rotation speed of the variable speed motor. It is decreasing. In this Patent Document 1, it is more preferable that the discharge pressure is stabilized as the discharge pressure rises by the pressure control system under the rotational speed condition of the variable speed motor between the cut-off start pressure and the full cut-off pressure. Therefore, it is preferable to set the characteristic such that the rotational speed is decreased stepwise or steplessly so that the minimum rotational speed can be maintained. And when the variable displacement pump is in the full cut-off state and does not require the discharge amount of hydraulic oil, the power consumption at the full cut-off is reduced by reducing the rotation speed of the pump using an inverter device. Is reduced. Further, the pressure at the discharge port of the pump is detected in order to detect that the pump is in the vicinity of the cutoff (see, for example, Patent Document 1).
JP 2003-172302 A

However, in the method disclosed in Patent Document 1, in the case of a pump having a discharge pressure-flow rate characteristic with a sharp cutoff characteristic as shown in FIG. 4, for example, a variable displacement pump with a compensator, the discharge flow rate is reduced. Since the pressure difference between the starting cutoff point 1 and the full cutoff point 2 at which the discharge flow rate becomes zero is small, the rotational speed is reduced by the pressure change from the cutoff point 1 to the full cutoff point 2, and at the time of full cutoff Even if the controller stores the full cut-off pressure at the time of product shipment in order to make the variable speed motor the minimum number of revolutions, the cut-off pressure and full cut-off pressure may vary depending on the characteristics of pressure setting elements such as the compensator spring load. There is a possibility that it will be out of the rotational speed control range even if it changes a little.
In addition, the pressure of the compensator load port, that is, the pressure in the control piston chamber, is detected as a method of detecting the pump cutoff point and full cutoff point even if there is a change in the pressure setting element such as the spring load of the compensator. A way to do this is conceivable.
Looking at the relationship between the pressure at the load port of the compensator and the discharge flow rate, a curve is created as shown in Fig. 5 in which the pressure change in the region from the cut-off point to the full cut-off point of the pump discharge pressure-flow rate characteristic is expanded. . For this reason, a pump with low discharge pressure-flow rate hysteresis consumes the minimum number of revolutions at full cutoff by reducing the number of revolutions in proportion to the pressure at the load port of the compensator, that is, the pressure in the control piston chamber. Electric power can be reduced. This method has an advantage that it can be applied to a pump of 2 pressures and 2 flows as it is.

However, in some variable displacement pumps, the hysteresis that occurs unexpectedly due to the sliding resistance of the support mechanism of the swash plate, the sliding resistance of the control piston, and the tilt angle of the swash plate are stabilized to pulsate the discharge pressure. Due to the hysteresis that is intentionally added to suppress the discharge pressure-flow rate hysteresis as shown in FIG. 6, the relationship between the pressure in the control piston chamber and the discharge flow rate also has a large hysteresis as shown in FIG. . The purpose of Patent Document 1 is not to control the pressure with the rotation speed of the pump but to reduce the power consumption by reducing the rotation speed of the variable speed motor at the time of full cut-off. In the case of using, since it is not possible to expect responsiveness to control the discharge pressure by controlling the rotational speed, the rotational speed is changed according to the change in the pump state. Further, since the swash plate does not react within the hysteresis width, it appears to be a constant discharge pump, and the control performance inherent to the variable displacement pump cannot be used. When the load (throttle) on the discharge side is constant, when trying to control the rotation speed corresponding to the pressure in the control piston chamber in this state, increasing the rotation speed increases the discharge flow rate and the discharge pressure. The pressure in the piston chamber also increases. Further, when the rotational speed is lowered, the discharge flow rate is reduced, the discharge pressure is lowered, and the pressure in the control piston chamber is also lowered. Normally, the discharge pressure is controlled by controlling the rotation speed of the constant discharge pump due to the influence of the acceleration / deceleration time required by the inverter device, the dead time due to the sampling time of the inverter device, and the response delay due to the inertial force of the three-phase induction motor. There is a problem that the performance as much as possible cannot be obtained and the self-excited vibration (limit cycle) is entered.
The present invention has been made to solve the above-mentioned problems, such as the influence of the acceleration / deceleration time required by the inverter device, the dead time due to the sampling time of the inverter device, the response delay due to the inertial force of the three-phase induction motor, etc. It is an object of the present invention to provide an inverter drive control method for a hydraulic pump that does not repeat self-excited vibration (limit cycle) and repeat rotation speed changes.

  In order to solve the above-mentioned problems, the invention according to claim 1 is characterized in that, in the inverter drive of the variable displacement pump, a pressure detection port is provided between the load port of the compensator and the pressure chamber of the control piston that controls the tilt angle of the swash plate. A pressure sensor having a pressure chamber, detecting the pressure in the pressure chamber of the control piston, calculating a rotation speed command to the inverter device based on the detected pressure in the pressure chamber of the control piston, If the calculated number of rotations is greater than a certain value d than the currently commanded number of rotations, a value obtained by subtracting a certain value d from the calculated value is used as the number of rotations command to the inverter device. If the calculated rotation speed is smaller than the currently commanded rotation speed by a certain value d, the value obtained by adding a certain value d to the calculated value is inverted. If the absolute value of the difference between the calculated rotational speed and the currently commanded rotational speed is less than a certain value d, a backlash calculation that does not change the rotational speed command value to the inverter device is performed. Thus, the rotational speed command to the inverter device is used.

In the variable pump, in the variable pump, by providing a pressure sensor having a pressure detection port between the pressure port of the control piston that controls the tilt angle of the load port of the compensator and the swash plate, the pressure in the control piston chamber is detected, By calculating the rotational speed command to the inverter based on the detected pressure in the control piston chamber, the rotational speed can be reliably controlled even if the cutoff pressure or full cutoff pressure changes slightly due to changes in the spring load of the compensator. In addition, by providing a backlash calculation, the delay time of the inverter device is allowed and the acceleration / deceleration function required by the inverter device even in the control of a pump with large pump discharge pressure-discharge flow rate hysteresis. Even if the motor is used, the rotational speed of the motor may Since the minimum rotation speed can be maintained at full cut-off, even with a sharp cut-off variable pump with a compensator, it is possible to control the rotation speed by the inverter while maintaining the pressure-flow rate characteristics without the rotation speed control by the inverter. Reduced power consumption at full cut-off.

A preferred embodiment of an inverter drive control method for a hydraulic pump according to the present invention will be described in detail with reference to the drawings.
FIG. 1 is a longitudinal sectional view showing a schematic structure of a variable displacement piston pump 10 according to an embodiment of the present invention. In FIG. 1, the pressure oil discharged to the discharge port 11 is guided to the pressure chamber 13 of the compensator 12 and acts on one end surface of the spool 14. In this case, the elastic force of the spring member 15 (first spring member) is biased to the other end surface of the spool 14.

The load port 16 of the compensator 12 is connected to the pressure chamber 18 of the control piston 17. Further, the end 19 of the exposed portion of the control piston 17 is in contact with the end of the swash plate 20. The swash plate 20 is provided with a spring member 21 (second spring) that acts in a direction to push the control piston 17 into the pressure chamber 18 side.
When the discharge port 11 is fully opened and the discharge pressure is low, the spool 14 of the compensator 12 is pressed toward the pressure chamber 13 by the elastic force of the spring member 15. For this reason, the load port 16 has the same pressure as the drain circuit (not shown), and the pressure in the pressure chamber 18 of the control piston 17 is also the same as the pressure of the drain circuit (not shown).

  The swash plate 20 is pressed by the elastic force of the spring member 21 and has the largest tilt angle, and the discharge flow rate is also large. When the discharge port of a pump (not shown) is gradually throttled from the fully open state, the pressure at the discharge port increases. Therefore, when the discharge pressure, that is, the product of the pressure chamber 13 of the compensator 12 and the cross-sectional area of the spool 14 becomes larger than the elastic force of the spring member 15, the spool 14 starts to move toward the spring member 15. When the discharge pressure further increases, the communication between the load port 16 of the compensator 12 and the drain port 22 is closed, and the load port 16 of the compensator 12 communicates with the supply port 23.

  In the process of opening the load port 16 of the compensator 12 to the drain port 22 from the fully open state to the supply port 23 side, the swash plate 20 becomes substantially vertical and reaches a full cut-off point where no discharge occurs. The pressure of the load port 16 of the compensator 12 is determined by the balance between the product of the cross-sectional area of the control piston 17 and the pressure of the pressure chamber 18 of the control piston 17 and the elastic force of the spring member 21. When the pressure in the pressure chamber 18 is 30 to 50% of the discharge pressure, a full cutoff state is obtained. Therefore, it is possible to detect the cutoff point and the full cutoff point by detecting the load port 16 of the compensator 12, that is, the pressure chamber 18 of the control piston 17, with the pressure sensor 25. It varies depending on the sliding resistance between the plate 20 and the slide bearing 24, the sliding resistance of the control piston 17, the amount of internal leakage of the control piston 17 from the pressure chamber 18, the elastic force of the spring member 21, the spring constant, and the like. . Therefore, depending on the structure of the pump, there are cases where the characteristics are as shown in FIGS. 4 and 5, but there are also cases where the characteristics are as shown in FIGS.

FIG. 2 is a schematic diagram showing changes in the discharge flow rate and the rotational speed and the pressure in the pressure chamber 18 of the control piston 17 when the rotational speed is controlled when the hysteresis is large. When the load port 16 of the compensator 12 is fully open to the drain port 22, the point A is indicated.
Therefore, when the discharge pressure rises, the pressure in the pressure chamber 18 of the control piston 17 also rises to B point, but there is no change in the swash plate angle and no change in the discharge flow rate due to hysteresis.
If the solid line drawn in the center of the hysteresis curve is the target rotational speed, the point B is higher than the target rotational speed, so the operation is performed to decrease the rotational speed. If the angle of the swash plate 20 is fixed and the rotational speed is lowered, the discharge flow rate is also lowered, so that the direction of the C point is reached. At point C, the number of revolutions has been reduced too much, so an operation for correction toward point D is performed. In this way, it is sufficient to settle at the point F. Usually, however, due to the influence of the acceleration / deceleration time required by the inverter device, the dead time due to the sampling time of the inverter device, the response delay due to the inertial force of the three-phase induction motor, etc. The control of the discharge pressure cannot be obtained by controlling the rotation speed of the constant discharge pump, and the self-excited vibration (limit cycle) is entered, so that the reciprocating motion is performed before and after the solid line.

  Therefore, if the rotational speed command to the inverter is not changed within the dotted line range, the self-excited vibration (limit cycle) may be prevented. If going from point B to point C up to point C ', it means that there was a change outside the hysteresis range, so the angle of the pump swashplate changed and the pump condition Since it has changed to another state, another countermeasure such as gain adjustment is required.

FIG. 3 is a block diagram of a control device related to the inverter drive control method for the hydraulic pump of the present invention. 3, the same components as those in FIG. 1 are denoted by the same reference numerals. In FIG. 3, reference numeral 27 denotes a three-phase induction motor, which drives the variable displacement piston pump 10. As shown in FIG. 3, the detection signal detected by the pressure sensor 25 is transmitted to the command value calculation unit 28, the value calculated by the designated value calculation unit 28 is sent to the backlash element unit 29, and the backlash element A value calculated by the unit 29 is input to the inverter device 30, and a signal detected by the inverter device 30 is sent to the three-phase induction motor 27.
A pressure sensor 25 is attached to the load port 16 of the compensator 12 to detect the pressure in the pressure chamber 18 of the control piston 17 of the variable displacement piston pump 10. The command value calculation unit 28 reduces the rotational speed from about 1 MPa, which is the instantaneous maximum value of the drain back pressure, based on the output of the pressure sensor 25, and is about 0.5 to 0.8 times the pressure at full cut-off. The pressure-rotation number of the pressure chamber 18 of the control piston 17 is calculated so as to be the minimum rotation number.

The outline of the backlash calculation in the backlash element unit 29 will be described. The two-dot chain line of the backlash element portion 29 shown in FIG. 3 represents the relationship between the calculated rotational speed command when the backlash calculation is not performed and the rotational speed command to the inverter device, and has a one-to-one correspondence. ing. Originally, it should be a straight line extending from the intersection of the X axis and the Y axis (not shown), but in order to avoid that the rotation speed command to the inverter device becomes a negative rotation command, d Is offset by the width of. Since the actual minimum rotational speed is larger than the backlash width 2d, there is no need to add an offset by calculation.
Since the rotation speed (calculated value) is offset by the width of d, it starts from the intersection of the two-dot chain line and the X axis. When the rotational speed (calculated value) gradually increases and becomes larger than the two-dot chain line by the width d, a rotational speed command is issued to the inverter device. Since the rotational speed command to the inverter device is smaller than the rotational speed (calculated value) by d, it rises along the right solid line. The rotational speed command to the inverter device is the rotational speed at the point where the Y axis is intersected when a parallel line is drawn from the point of interest to the X axis. Here, even if the rotational speed (calculated value) decreases, the rotational speed command is not changed to the inverter device until it becomes smaller than the d width from the two-dot chain line to the left, and when the rotational speed becomes smaller than the d width, Is added to the inverter device as a rotational speed command, so that it has hysteresis as shown in the figure and can be used as a backlash element.

Next, the backlash element unit 29 performs an operation for giving backlash from the rotational speed command currently given to the inverter device 30 and the calculated rotational speed to obtain a command voltage to the inverter device 30. In the inverter device 30, an acceleration / deceleration time according to an acceleration / deceleration parameter is changed to a three-phase AC voltage having a frequency in accordance with a command voltage and applied to the three-phase induction motor 27.
The feature of this control is that the number of revolutions of the variable displacement piston pump 10 at a certain discharge amount is not fixed, but only for the purpose of making the minimum number of revolutions at the full cut-off point. It is to leave. For example, if the minimum rotation speed is 1/4 of the maximum rotation speed and the discharge flow rate is 1/4, the variable displacement piston pump 10 is at the maximum discharge amount and the rotation speed is 1/4. In addition, the case where the rotational speed is the maximum rotational speed and the capacity of the variable displacement pump is ¼ is allowed.

It is a longitudinal section showing a schematic structure of a variable capacity type piston pump concerning an embodiment of the invention. It is the schematic which shows the change of the discharge flow volume and rotation speed at the time of rotational speed control when a hysteresis is large, and the pressure in the pressure chamber of a control piston. It is a block diagram of the control apparatus regarding the inverter drive control method of the hydraulic pump of this invention. It is a discharge pressure-discharge flow rate characteristic diagram of a variable capacity pump with small hysteresis. FIG. 5 is a discharge flow rate related to the present invention of the pump of FIG. 4 -pressure characteristics in the pressure chamber of the control piston. It is a discharge pressure-discharge flow rate characteristic diagram of a variable capacity pump with a large hysteresis. FIG. 7 is a discharge flow rate related to the present invention of the pump of FIG. 6 -pressure characteristics in the pressure chamber of the control piston.

Explanation of symbols

1 Cut-off point 2 Full cut-off point
DESCRIPTION OF SYMBOLS 10 Variable displacement type piston pump 11 Discharge port 12 Compensator 13, 18 Pressure chamber 14 Spool 15, 21 Spring member 16 Load port 17 Control piston 20 Swash plate 22 Drain port 23 Supply port 25 Pressure sensor 28 Command value calculation part 29 Backlash element Part 30 Inverter device

Claims (1)

In the inverter drive of a variable displacement pump, a pressure sensor with a pressure detection port is provided between the pressure port of the control piston that controls the tilt angle of the compensator load port and the swash plate, and the pressure in the pressure chamber of the control piston is detected. The rotation speed command to the inverter device is calculated based on the detected pressure in the pressure chamber of the control piston, and the calculated rotation speed is compared with the rotation speed currently commanded. If the rotation speed is greater than a certain value d, the value obtained by subtracting the value d from the calculated value is used as a rotation speed command to the inverter device, and the calculated rotation speed is a value that is greater than the rotation speed currently commanded. If it is smaller than d, the value obtained by adding a certain value d from the calculated value is used as the rotation speed command to the inverter device, and the calculated rotation speed and the current When the absolute value of the difference between the rotational speeds is less than a certain value d, a backlash calculation that does not change the rotational speed command value to the inverter device is performed to obtain the rotational speed command to the inverter device. An inverter drive control method for a hydraulic pump.

Images