JP4922963B2 - Pump tilt control device for hydraulic working machine - Google Patents

Description

  The present invention relates to a pump tilt control device for a hydraulic working machine such as a hydraulic excavator.

  2. Description of the Related Art Conventionally, there has been known an apparatus that controls pump tilting by a tilt control signal corresponding to an operation amount of an operation lever (see, for example, Patent Document 1). In the device described in Patent Literature 1, a proportional control valve is driven by outputting a tilt control signal corresponding to the operation amount of the control lever, and the pilot pressure acting on the switching valve is adjusted by driving the proportional control valve. The pump tilt is controlled to the target pump tilt by driving the switching valve.

JP-A-8-302755

  However, in the apparatus described in Patent Document 1, the pressure in the casing that opposes the pilot pressure acts on the switching valve. For this reason, when the pressure in the casing rises, the switching valve is not driven according to the command value, and the pump tilt may not be accurately controlled to the target pump tilt.

A pump tilt control device for a hydraulic working machine according to the present invention is a variable displacement hydraulic pump that supplies a drive pressure to a hydraulic actuator, a valve means that generates a control pressure for pump tilt control, and a drive for the valve means. In response, the capacity changing means for changing the pump capacity of the hydraulic pump, the command pressure output means for outputting the command pressure for driving the valve means, and the back pressure for obtaining the back pressure acting on the valve means against the command pressure. The apparatus includes a pressure acquisition unit and a correction unit that corrects the command pressure according to the back pressure acquired by the back pressure acquisition unit.
The command pressure output means includes a pilot hydraulic pump for generating a pilot pressure, an input means for inputting a target pump tilt, and a pressure reducing means for reducing the pilot pressure from the pilot hydraulic pump in accordance with the target pump tilt. be able to.
The back pressure acquisition means stores the discharge pressure detection means for detecting the discharge pressure of the hydraulic pump, the storage means for storing the relationship between the pump discharge pressure and the back pressure in advance, and the discharge pressure detected by the discharge pressure detection means. Further, back pressure calculating means for calculating the back pressure based on the relationship between the pump discharge pressure and the back pressure can be provided.
The back pressure acquisition means may include back pressure detection means for detecting back pressure.
Command pressure detecting means for detecting command pressure acting on the valve means, and control means for controlling the command pressure output means so that the command pressure detected by the command pressure detecting means becomes the command pressure corrected by the correcting means. Furthermore, it is good also as what has.

  According to the present invention, since the command pressure is corrected according to the back pressure acting against the command pressure to the valve means for pump tilt control, the pump tilt is considered in consideration of the effect of the back pressure. Can be accurately controlled to the target pump tilt.

Hereinafter, an embodiment of a pump tilt control device for a hydraulic working machine according to the present invention will be described with reference to FIGS.
FIG. 1 is an external side view of a hydraulic excavator that is an example of a hydraulic working machine to which a pump tilt control device according to the present embodiment is applied. The hydraulic excavator includes a traveling body 101, a swingable swinging body 102, and a work device 103 including a boom BM, an arm AM, and a bucket BK that are pivotally supported by the swinging body 102. Boom BM, arm AM, and bucket BK are driven by boom cylinder 103a, arm cylinder 103b, and bucket cylinder 103c, respectively.

  Fig.2 (a) is a figure which shows the structure of the pump tilt control apparatus based on this Embodiment. The output shaft of the engine 1 is connected to the input shafts of the variable displacement main pump 2 and the sub pump 3, and the hydraulic oil is discharged from the hydraulic pumps 2 and 3 by driving the engine 1. Pressure oil from the main pump 2 is supplied to a hydraulic actuator 5 such as a hydraulic cylinder (such as a boom cylinder) or a hydraulic motor (such as a swing motor) via a direction control valve 4.

  Pilot pressure from the sub pump 3 is supplied to the direction control valve 4 via the pilot valve 7. The pilot valve 7 is driven by the operation of the operation lever 6, and the flow of pressure oil to the hydraulic actuator 5 is controlled according to the operation amount of the operation lever 6. Although not shown, a relief valve is provided between the main pump 2 and the control valve 4 to limit the upper limit of the pump discharge pressure to the relief pressure Pr.

  A lock valve 9 is provided between the pilot valve 7 and the sub pump 3. The lock valve 9 is switched to the lock position by a lock operation of a gate lock lever (not shown) provided at the entrance of the driver's seat, and is switched to the unlock position by an unlock operation. When the lock valve 9 is switched to the locked position, the flow of pressure oil to the pilot valve 7 is prohibited. In this state, the pilot pressure is not supplied to the direction control valve 4 regardless of the operation of the operation lever 6, the direction control valve 4 is held at the neutral position, and the flow of pressure oil to the hydraulic actuator 5 is blocked. When the lock valve 9 is switched to the unlock position, the flow of pressure oil to the pilot valve 7 is allowed.

  The tilt of the main pump 2 is changed by a pump regulator. The pump regulator includes a tilt control piston 12, a hydraulic switching valve 13, and a proportional solenoid valve 14. The discharge pressure Pp of the main pump 2 acts on the small-diameter side oil chamber 12 a of the tilt control piston 12, and the discharge pressures of the main pump 2 and the sub pump 3 are applied to the large-diameter side oil chamber 12 b via the hydraulic switching valve 13. Works. The piston 12 is driven in accordance with the oil pressure acting on each oil chamber 12a, 12b, and the tilt of the main pump 2 is changed.

  The pilot pressure (secondary pressure Pa) from the sub pump 3 via the proportional solenoid valve 14 acts on the hydraulic pressure switching valve 13, and the hydraulic pressure switching valve 13 is switched according to the secondary pressure Pa. That is, when the secondary pressure Pa of the proportional solenoid valve 14 increases, the hydraulic switching valve 13 is switched to the position A side. As a result, the oil pressure acting on the oil chamber 12b increases and the pump tilt increases. On the other hand, when the secondary pressure Pa decreases, the hydraulic switching valve 13 is switched to the position B side. As a result, the oil pressure acting on the oil chamber 12b is reduced, and the pump tilt is reduced. When the pump tilt increases or decreases in this manner, the pump discharge amount changes between the minimum flow rate Qmin and the maximum flow rate Qmax.

  The main pump 2 and the regulator are integrally formed by a pump block 10, and the inside of the block 10 is filled with oil leaked from the pump 2. For this reason, as shown in FIG. 2B, the pressure in the block (casing pressure Pb) acts on the spool of the hydraulic pressure switching valve 13 as a back pressure against the secondary pressure Pa. Since oil in the pump block is discharged to the tank via the drain port and filter, the drain port pressure (drain pressure) is affected by the pressure loss (pressure loss) of the discharge path from the drain port to the tank and the viscosity of the hydraulic oil. When the pressure Pd) increases, the casing pressure Pd (internal pressure in the pump block) also increases. Hereinafter, description will be made assuming that the casing pressure Pb and the drain pressure Pd are equivalent.

  FIG. 3 is a diagram showing the relationship between the pump discharge pressure Pp and the drain pressure Pd. As shown in FIG. 3, when the pump discharge pressure Pp increases, the amount of oil leakage from the main pump 2 increases, and the drain pressure Pd increases proportionally. When the pump discharge pressure Pp is the maximum Pp1 (relief pressure Pr), the drain pressure is also the maximum Pd1.

  FIG. 4 is a diagram showing a tilt control characteristic that is a relationship between the secondary pressure Pa and the pump discharge amount Q. A characteristic a in the figure is a reference characteristic when the drain pressure Pd is 0, and a characteristic b is a characteristic when the drain pressure Pd is the maximum Pd1. As shown in the characteristic a, when the drain pressure Pd is 0, the secondary pressure is a predetermined value Pa1 and the pump discharge amount is Q1.

  On the other hand, as shown in the characteristic b, when the drain pressure Pd is Pd1, since the casing pressure (drain pressure Pd1) acts as a drag of the secondary pressure Pa, the secondary pressure Pa acting on the hydraulic pressure switching valve 13 is It decreases by the substantial drain pressure Pd1. For this reason, the tilt control characteristic is shifted to the right, and the pump discharge amount is smaller than Q1. If the proportional solenoid valve 14 is controlled based on the reference characteristic a when the drain pressure Pd increases in this way, there is a possibility that the desired pump discharge amount Q cannot be obtained. In particular, since the hydraulic switching valve 13 is switched by the pilot pressure from the sub pump 3 that is lower in pressure than the main pump 2, the influence of the casing pressure is great. Therefore, in this embodiment, as described below, a relationship (drain pressure characteristic) between the pump discharge pressure Pp and the drain pressure Pd as shown in FIG. 3 is determined in advance, and the pump tilt is controlled based on this relationship.

  The drain pressure characteristic is obtained as follows. First, the pressure sensor 25 for detecting the drain pressure Pd is attached to the drain port of the pump block 10, and the signal line is connected to the controller 20. Next, the hydraulic working machine is warmed up until the temperature T of the hydraulic oil falls within a predetermined range. That is, in consideration of the fact that the oil viscosity changes due to the oil temperature T and the drain pressure Pd is affected, the hydraulic working machine is operated until the oil temperature T reaches the oil temperature during normal operation (for example, 50 to 60 ° C.). Warm up. Further, since the pump discharge amount Q increases as the engine speed N increases, the engine speed N is set to the rated speed Na.

  Further, the boom raising and lowering operation lever 6 is operated to raise the boom BM to the maximum, and the oil discharged from the main pump 2 is relieved from the relief valve. That is, the maximum value of the drain pressure Pd is acquired. In this state, the pump discharge pressure Pp (= Pp1) and the drain pressure Pd (= Pd1) are detected by the pressure sensors 23 and 25, respectively, and the straight line connecting this and the origin is defined as the drain pressure characteristic.

  The controller 20 shown in FIG. 2 includes an arithmetic processing unit having a CPU, ROM, RAM, and other peripheral circuits. The controller 20 includes a rotation speed sensor 21 that detects the rotation speed N of the engine 1, a pressure sensor 22 that detects an operation pressure Pn (positive control pressure) corresponding to the operation amount of the operation lever 6, and a discharge pressure of the main pump 2. A pressure sensor 23 for detecting Pp, a pressure sensor 24 for detecting the secondary pressure Pa acting on the proportional solenoid valve 14, a pressure sensor 25 for detecting the drain pressure Pd, and a temperature sensor 26 for detecting the hydraulic oil temperature T , A command switch 27 for instructing a process (automatic adjustment) for automatically calculating a drain pressure characteristic, a mode switch 28 for selecting one of a learning mode and a normal mode, and a limit for detecting a lock operation of the gate lock lever A switch 29 is connected. The controller 20 executes the following processing based on signals from the sensors 21 to 26 and the switches 27 to 29.

(1) Automatic Adjustment FIG. 5 is a flowchart illustrating an example of automatic adjustment executed by the controller 20. The process shown in this flowchart is started when the command switch 27 is turned on. In addition, when performing automatic adjustment, the drain pressure sensor 25 is connected to the controller 20 in advance. The drain pressure sensor 25 is removed when the automatic adjustment is completed.

  In step S1, it is determined whether or not the hydraulic oil temperature T detected by the temperature sensor 26 is within a predetermined range (50 to 60 ° C.). In step S2, it is determined whether or not the engine speed N detected by the speed sensor 21 is the rated speed Na. In step S3, it is determined whether or not the boom sensor BM raising operation is detected by the pressure sensor 22. In step S4, it is determined whether or not the discharge pressure of the main pump is equal to or higher than the relief pressure. When all of step S1 to step S4 are affirmed, the process proceeds to step S5, and when any one is denied, the process proceeds to step S10.

  In step S5, it is determined whether or not the detection value Pd of the pressure sensor 25 for detecting the drain pressure is within a normal range. When step S5 is affirmed, the process proceeds to step S6, and the detection value Pd (= Pd1) of the pressure sensor 25 is read and stored in the memory. In step S7, it is determined whether or not the detection value Pp of the pressure sensor 23 for detecting the pump discharge pressure is within a normal range. If step S7 is affirmed, the process proceeds to step S8, and the detection value Pp (= Pp1) of the pressure sensor 23 is read and stored in the memory.

  Next, in step S9, for example, a signal is output to the display monitor to notify the worker that the automatic adjustment has been normally completed. If any of step S1 to step S5 or step S7 is denied, the process proceeds to step S10 to notify the worker that the automatic adjustment has ended abnormally. The drain pressure characteristic of FIG. 3 is obtained by the above processing. This drain pressure characteristic is stored in the drain pressure calculation circuit 36 of FIG. 12, and the pump tilt is controlled as will be described later.

  In the present embodiment, pump tilt control is performed in consideration of characteristic variations due to individual differences of the proportional solenoid valve 14. Hereinafter, this point will be described. 6 is a diagram illustrating an example of input / output characteristics of the proportional solenoid valve 14, and FIG. 7 is a diagram illustrating a relationship between the secondary pressure Pa and the pump tilt θ.

  In FIG. 6, a characteristic A0 is a reference characteristic, and the secondary pressure Pa increases as the drive current i to the proportional solenoid valve 14 increases. Since there are individual differences in the characteristics of the proportional solenoid valve 14, the characteristics vary within the tolerance ± Δα with respect to the reference characteristic A 0, and the actual characteristic A deviates from the reference characteristic A 0. For this reason, for example, when the drive current i1 is output to the proportional solenoid valve 14 based on the reference characteristic A0 in order to generate the secondary pressure Pa1, the actual secondary pressure becomes Pa1 'and deviates from the target value Pa1.

  As a result, as shown in FIG. 7, the actual pump tilt θ 1 ′ deviates from the target pump tilt θ 1, and it becomes impossible to perform good work according to the operation of the operation lever 6. In consideration of this point, in the present embodiment, a correction characteristic that takes into account the variation of the proportional solenoid valve 14 is set in advance (learning control), and the pump tilt θ is controlled based on the correction characteristic obtained by the learning control ( Normal control).

(2) Learning Control FIG. 8 is a flowchart illustrating an example of learning control processing. A reference characteristic F0 (design value) of the proportional solenoid valve 14 as shown in FIG. 9 is stored in the controller 10 in advance, and driving current (reference control signal iAmin corresponding to three points on this characteristic, that is, the minimum pump tilt θmin is stored. ), The drive current (reference control signal iAmax) corresponding to the pump maximum tilt θmax, and the drive current (reference control signal iAmea) corresponding to the intermediate tilt θmea that is intermediate between θmin and θmax are stored as reference values. . Design secondary pressures (reference control pressures) Pmin, Pmea, and Pmax respectively corresponding to θmin, θmea, and θmax are also stored as reference values.

  The process of FIG. 8 is started when the learning mode is selected by operating the mode switch 28. In step S11, it is determined whether or not the hydraulic oil temperature T detected by the temperature sensor 27 is within a predetermined range (50 to 60 ° C.). In step S12, it is determined whether or not the engine speed N detected by the speed sensor 21 is the rated speed Na. Steps S11 and S12 are processes for performing learning control in accordance with actual work conditions. If both step S11 and step S12 are affirmed, the process proceeds to step S13, and if either is denied, the process proceeds to step S11. Return.

  In step S13, it is determined based on a signal from the limit switch 29 whether or not the gate lock lever is locked. This is a process for preventing the machine from malfunctioning during the learning control, and the learning control is performed only in a state where the supply of the pilot pressure to the directional control valve 4 is cut off. When step S13 is affirmed, the process proceeds to step S14, and when negative, the process returns to step S11.

  In step S14, a drive current i11 (for example, iAmin) corresponding to the minimum pump tilt θmin or the tilt θ in the vicinity thereof is calculated based on the reference characteristic F0 of FIG. 9 and this drive current i11 is output to the proportional solenoid valve 14. In step S15, a predetermined time (for example, 5 seconds) is counted until the secondary pressure data is stabilized, the secondary pressure Pa is read after the lapse of the predetermined time, and is stored in the memory as the actually measured secondary pressure P11.

  In step S16, a drive current i12 (for example, iAmax) corresponding to the pump maximum tilt θmax or the tilt θ in the vicinity thereof is calculated based on the reference characteristic F0 of FIG. 9 and this drive current i12 is output to the proportional solenoid valve 14. In step S17, a predetermined time (for example, 5 seconds) is counted until the secondary pressure data is stabilized, the secondary pressure Pa is read after the lapse of the predetermined time, and the measured secondary pressure P12 is stored in the memory.

  In step S18, a drive current i13 (for example, iAmea) corresponding to the intermediate tilt θmea or the tilt θ in the vicinity thereof is calculated based on the reference characteristic F0 of FIG. 9, and this drive current i13 is output to the proportional solenoid valve 14. In step S19, a predetermined time (for example, 5 seconds) is counted until the secondary pressure data is stabilized, the secondary pressure Pa is read after the lapse of the predetermined time, and is stored in the memory as the actually measured secondary pressure P13. The relationship between the secondary pressure and the control signal (current) is obtained by connecting the secondary pressure data P11, P12, and P13 obtained as described above with a straight line as shown in FIG.

In step S20, drive currents imin, imea and imax corresponding to predetermined reference control pressures Pmin, Pmea and Pmax are calculated by the following equation (I) using the relationship shown in FIG.
imin = i11− (P11−Pmin) × (i13−i11) / (P13−P11)
imea = i13− (P13−Pmea) × (i13−i11) / (P13−P11); when P13> Pmea imea = i13 + (Pmea−P13) × (i12−i13) / (P12−P13); P13 < Pmea)
imax = i12 + (Pmax−P12) × (i12−i13) / (P12−P13) (I)

  The imin, imea, and imax obtained here mean drive currents corresponding to the minimum tilt θmin, the intermediate tilt θmea, and the maximum tilt θmax of the proportional solenoid valve 14, respectively. That is, when currents imin, imea, and imax are output to the proportional solenoid valve 14, the secondary pressures are Pmin, Pmea, and Pmax, respectively, and the actual pump tilts are θmin, θmea, and θmax, respectively.

  In step S21, current correction values Δimin, Δimea, Δimax are calculated by subtracting predetermined driving currents iAmin, iAmea, iAmax from the driving currents imin, imea, imax, respectively, and stored in the memory. As a result, as shown in FIG. 11, a correction characteristic f1 unique to the proportional solenoid valve 14 is obtained, and this characteristic is stored in the memory of the controller 20. This completes the learning control. Note that, for example, a lamp in the driver's seat may be turned on at the end of the learning control to notify the worker that the learning control has ended.

(3) Normal Control FIG. 12 is a block diagram showing normal control processing in the controller. After the learning control is finished, when the normal mode is selected by operating the mode switch 28, the normal control is started. A signal from the rotation speed sensor 21 is input to the torque calculation circuit 31. The torque calculation circuit 31 stores in advance the relationship between the engine speed N and the output torque Tr as shown in the figure. Based on this relationship, the torque calculation circuit 31 calculates an output torque Tr corresponding to the engine speed N and outputs it to the capacity calculation circuit 32.

  A pump discharge pressure Pp detected by the pressure sensor 23 is input to the capacity calculation circuit 32. In the capacity calculation circuit 32, in order to prevent the pump absorption torque from exceeding the engine output torque Tr, a horsepower characteristic with a constant engine output torque Tr is set in advance as illustrated. The capacity calculation circuit 32 calculates the target pump tilt θ1 corresponding to the pump discharge pressure Pp based on this characteristic.

  A positive control pressure Pn detected by the pressure sensor 22 is input to the capacity calculation circuit 33. In the capacity calculation circuit 33, as shown in the drawing, the relationship between the positive control pressure Pn and the target pump tilt θ2 due to the operation of the operation lever 6, that is, the relationship in which the target pump tilt θ2 increases as the positive control pressure Pn increases. Is remembered. The capacity calculation circuit 33 calculates a target pump tilt θ2 corresponding to the positive control pressure Pn based on this characteristic.

  The target pump tilts θ1 and θ2 calculated by the capacity calculation circuits 32 and 33 are input to the selection circuit 34, respectively. The selection circuit 34 selects the smaller one of the target pump tilts θ 1 and θ 2 as the target pump tilt θ, and outputs the target pump tilt θ to the command pressure calculation circuit 35.

  The command pressure calculation circuit 35 stores in advance a reference characteristic of the command pressure P0 as shown in the drawing, that is, a characteristic that the command pressure P0 increases as the target pump tilt θ increases. Based on this characteristic, the command pressure calculation circuit 35 calculates a target command pressure P0 (command value of the secondary pressure Pa) corresponding to the target pump tilt θ.

  The drain pressure calculation circuit 36 receives the pump discharge pressure Pp detected by the pressure sensor 23. The drain pressure calculation circuit 36 stores a relationship (FIG. 3) between the pump discharge pressure Pp and the drain pressure Pd obtained in advance by automatic adjustment control. The drain pressure calculation circuit 36 calculates a drain pressure Pd corresponding to the pump discharge pressure Pp based on this characteristic. In the adding circuit 37, the drain pressure Pd is added to the target command pressure P0 to correct the target command pressure P0.

  The feedback control circuit 40 feedback-controls the target command pressure P0 and outputs the command pressure Px. That is, the subtraction circuit 41 subtracts the secondary pressure Pa detected by the pressure sensor 24 from the target command pressure P0 to calculate a pressure deviation ΔP (= P0−Pa). The gain circuit 42 multiplies the deviation ΔP by the feedback gain K to calculate the deviation ΔPK. The addition circuit 43 adds the deviation ΔPK to the target command pressure P0 and outputs the command pressure Px. Thereby, the feedback control circuit 40 outputs the feedback command pressure Px so that the secondary pressure Pa detected by the pressure sensor 24 becomes equal to the target command pressure P0.

  The command pressure Px is output to the reference calculation circuit 44 and the correction calculation circuit 45, respectively. The reference calculation circuit 44 stores in advance the relationship (design value) between the command pressure Px of the proportional solenoid valve 14 and the drive current I0 as shown in the figure. The reference calculation circuit 44 calculates a target drive current I0 corresponding to the command pressure Px based on the reference characteristic f0 of the drive current.

  The correction calculation circuit 45 stores a relationship (FIG. 11) between the command pressure Px and the correction current ΔI0 determined in advance in the learning mode. The correction calculation circuit 45 calculates a correction current ΔI0 corresponding to the command pressure Px based on the correction characteristic of the drive current. The adder circuit 46 adds the target drive current I0 and the correction current ΔI0, calculates the corrected target drive current I, and outputs it to the proportional solenoid valve 14. The normal control process described above is repeated during work.

  The operations according to the present embodiment are summarized as follows. First, in the learning mode, the process of FIG. 8 is performed by the controller 20, and the correction characteristic f1 unique to the proportional solenoid valve 14 is obtained. In this case, the mode switch 28 is switched to the learning mode, the hydraulic oil temperature T is kept within a predetermined range, the engine speed N is controlled to the rated speed Na, and the gate lock lever is locked. (Step S11 to Step S13).

  When the above conditions are established, the controller 20 outputs predetermined drive currents i11, i12, and i13 to the proportional solenoid valve 14, and detects the secondary pressures P11, P12, and P13, and calculates the secondary pressure Pa and the current i. The relationship (FIG. 10) is obtained. From this relationship, drive currents imin, imea, imax corresponding to the reference control pressures Pmin, Pmea, Pmax are calculated (step S20). The reference drive currents iAmin, iAmea, iAmax are subtracted from the drive currents imin, imea, imax, respectively, and the current correction values Δimin, Δimea, Δimax are stored in the memory (step S21).

  Next, the automatic adjustment process shown in FIG. 5 is performed to obtain the drain pressure characteristic (FIG. 3). In this case, the pressure sensor 25 for detecting the drain pressure is connected to the controller 20, the command switch 27 is operated, the hydraulic oil temperature T is kept within a predetermined range, and the engine speed N is set to the rated speed Na. And the boom BM is raised to release the discharge pressure of the main pump 2 (steps S1 to S4).

  When the above conditions are satisfied, the controller 20 detects the drain pressure Pd and the pump discharge pressure Pp and stores them in the memory (steps S6 and S8). Thereafter, the worker removes the pressure sensor 25 from the controller 20. Note that learning control and automatic adjustment are performed for setting correction characteristics and drain pressure characteristics used in normal control, and are usually performed by a manufacturer at the time of factory shipment.

  During normal work, the mode switch 28 is switched to the normal mode. In the normal mode, the controller 20 outputs the target drive current I to the proportional solenoid valve 14 so that the secondary pressure Pa detected by the pressure sensor 24 becomes equal to the target command pressure P0 corresponding to the operation amount of the operation lever 6. That is, the command pressure Px is output by feedback control so that the secondary pressure Pa detected by the pressure sensor 24 becomes equal to the target command pressure P0, and the target drive current I0 corresponding to the command pressure Px is determined by the learning mode. The corrected target drive current I (= I0 + ΔI0) is output to the proportional solenoid valve 14 by correcting the corrected current ΔI0 with the characteristic f1.

  At this time, the controller 20 calculates the drain pressure Pd based on the drain pressure characteristic, and corrects the target command pressure P0 by adding the drain pressure Pd to the target command pressure P0. For this reason, the secondary pressure Pa acting on the hydraulic pressure switching valve 13 increases by the drain pressure Pd corresponding to the back pressure, and the casing pressure (drain pressure Pd) acting on the hydraulic pressure switching valve 13 is cancelled. As a result, the pump discharge amount Q can be changed along the reference characteristic a shown in FIG. 4, and a desired pump discharge amount Q can be obtained.

  The relationship between the discharge pressure P and the discharge amount Q of the main pump 2 in this case is shown in FIG. The characteristic a in the figure is a PQ characteristic (reference characteristic) when the drain pressure Pd is 0, and further is a PQ characteristic when the drain pressure Pd is Pd1 and the command pressure P0 is corrected with the drain pressure Pd1. The characteristic b is a PQ characteristic when the drain pressure Pd is Pd1 and the command pressure P0 is not corrected.

  When the command pressure P0 is not corrected, the secondary pressure Pa acting on the hydraulic pressure switching valve 13 is insufficient by the drain pressure Pd. Therefore, the actual pump tilt does not become the target pump tilt θ, and the pump discharge amount Q decreases by ΔQ from the target value when the drain pressure Pd is 0, that is, the target value. On the other hand, when the command pressure P0 is corrected as in the present embodiment, the secondary pressure Pa with the drain pressure Pd added to the hydraulic pressure switching valve 13 acts. Therefore, the actual pump tilt becomes the target pump tilt θ, and the pump discharge amount Q can be accurately controlled to the target value.

According to the present embodiment, the following operational effects can be achieved.
(1) The drain pressure Pd is calculated from the drain pressure characteristic set in the drain pressure calculation unit 36, and the command pressure P0 corresponding to the target pump tilt θ is added by the amount corresponding to the drain pressure Pd and output. As a result, a decrease in the switching amount of the hydraulic switching valve 13 due to the casing pressure (drain pressure Pd) acting on the hydraulic switching valve 13 is suppressed, and the pump tilt can be accurately controlled to the target pump tilt θ.
(2) Since the drain pressure Pd is detected by attaching the drain pressure detection hydraulic sensor 25 during automatic adjustment, the drain pressure Pd is calculated based on the drain pressure characteristics in normal control. It is not necessary to provide the hydraulic sensor 25, and the cost can be reduced.
(3) The low pressure pilot pressure from the sub pump 3, not the pressure oil from the main pump 2, is reduced by the proportional solenoid valve 14 and applied to the hydraulic pressure switching valve 13, and the hydraulic pressure switching valve 13 is switched. As a result, it is not necessary to increase the pressure resistance of the proportional solenoid valve 14 and the hydraulic switching valve 13 so much, and it can be configured at low cost.
(4) Automatic adjustment is performed when the hydraulic oil temperature T is within a predetermined range, the engine speed N is the rated speed Na, and the boom is raised. That is, since the automatic adjustment is performed according to the actual working conditions, the drain pressure characteristic can be obtained with high accuracy.

(5) In the learning control, the correction characteristic f1 for the pump tilt control is obtained using the detection value Pa of the pressure sensor 24, and in the normal control, the drive current I is obtained by feedback control using the detection value Pa of the pressure sensor 24. In addition to correction, the drive current I is corrected based on the correction characteristic f1. Thus, since the tilt control is performed without using the tilt angle sensor, the tilt control device can be configured at low cost. Further, since the pressure sensor 24 has better temperature characteristics than the tilt angle sensor, the pump tilt can be accurately corrected even when the pressure sensor 24 is operated under a high temperature condition.
(6) Since the command pressure Px is output by feedback control and the drive current I is corrected, when the target pump tilt θ changes due to the operation of the operation lever 6, the actual pump tilt can be responsive to the target pump tilt. It can be controlled to θ.
(7) Since the tilt control is performed based on the inherent correction characteristic f1 of the proportional solenoid valve 14, there is little variation in dynamic characteristics among individual products, and uniform operating characteristics can be obtained.
(8) Since the reference control pressure is set at three points (Pmin, Pmea, Pmax) to obtain the correction characteristic f1, the correction characteristic f1 corresponds well to the characteristic of the proportional solenoid valve 14, and the drive current I is accurately corrected. can do.

  In the above, the pressure sensor 25 for detecting the drain pressure is removed from the controller 20 during normal control, and the drain pressure Pd is obtained by calculation. However, the drain pressure Pd is directly detected by the pressure sensor 25 during normal control. May be. That is, the automatic adjustment process for obtaining the drain pressure characteristic may be omitted. An example of processing in the controller 20 in that case is shown in FIG.

  In FIG. 14, the drain pressure calculation unit 36 is not provided, and the drain pressure Pd detected by the pressure sensor 25 is input to the addition circuit 37. As a result, even when the relationship between the pump discharge pressure Pp and the drain pressure Pd deviates from the characteristics shown in FIG. 3, the command pressure P0 can be accurately corrected by the drain pressure Pd, and the pump tilt can be controlled with high accuracy. can do. In such a configuration, since automatic adjustment is not necessary, the command pressure P0 can be corrected immediately.

  In the above embodiment, the hydraulic pressure switching valve 13 is switched by the secondary pressure Pa from the proportional solenoid valve 14 to generate the control pressure to the piston 12. However, the back pressure against the secondary pressure Pa is applied. Any hydraulic switching valve 13 may be used as the valve means for generating the control pressure as long as it is configured to act. The pump tilt (pump capacity) is changed by driving the tilt control piston 12 in accordance with the switching of the hydraulic switching valve 13, but the capacity changing means is not limited to this. The pressure oil from the sub pump 3 is reduced by the proportional solenoid valve 14 and the secondary pressure Pa (command pressure P0) is output to the hydraulic pressure switching valve 13. However, the command pressure output means is not limited to this. For example, the valve means may be switched by pressure oil from the main pump 2.

  The pump discharge pressure Pp is detected by the pressure sensor 23 as the discharge pressure detection means, and the relationship between the pump discharge pressure Pp and the drain pressure Pd is stored in advance in the memory as the storage means, and the pump discharge pressure is determined based on this relationship. The drain pressure Pd corresponding to Pp is calculated by the drain pressure calculation circuit 36 (back pressure calculation means), but the back pressure acquisition means is not limited to this. As shown in FIG. 14, the back pressure may be acquired by detecting the drain pressure Pd by the pressure sensor 25 as the back pressure detecting means. As long as the command pressure P0 is corrected according to the back pressure acting on the hydraulic pressure switching valve 13, the configuration of the controller 20 as the correction means may be any.

  Although the positive pump pressure Pn is generated by the operation of the operation lever 6 and the target pump tilt is input, other input means may be used. Although the pilot pressure from the sub pump 3 is reduced by the proportional solenoid valve 14, the pressure reducing means is not limited to this. The secondary pressure Pa (command pressure) is detected by the pressure sensor 24 as command pressure detection means, and the proportional solenoid valve 14 is controlled so that the detected secondary pressure Pa becomes the corrected command pressure P0. However, any configuration of the controller 20 as the control means may be used.

  The example in which the tilt control device is applied to a hydraulic excavator has been described above, but the present invention can be similarly applied to other hydraulic working machines having a variable displacement pump. That is, as long as the features and functions of the present invention can be realized, the present invention is not limited to the pump tilt control device for the hydraulic working machine according to the embodiment.

1 is an external side view of a hydraulic excavator to which a pump tilt control device according to the present embodiment is applied. The figure which shows the structure of the pump tilt control apparatus which concerns on this Embodiment. The figure which shows the relationship between the discharge pressure of a hydraulic pump, and drain pressure. The figure which shows the relationship between the secondary pressure and pump discharge amount which act on the pilot port of a hydraulic switching valve. The flowchart which shows an example of the process of the automatic adjustment in a controller. The figure which shows the relationship between the drive current and secondary pressure which act on a proportional solenoid valve. The figure which shows the relationship between secondary pressure and pump tilting. The flowchart which shows an example of the learning control in a controller. The figure which shows the relationship between the target inclination and electric current in learning control. The figure which shows the relationship between the secondary pressure and electric current in learning control. The figure which shows the correction characteristic of a proportional solenoid valve. The block diagram which shows an example of the normal control in a controller. The PQ diagram showing operation | movement of this Embodiment. The figure which shows the modification of FIG.

Explanation of symbols

2 Main pump 3 Sub pump 6 Operation lever 12 Tilt control piston 14 Proportional solenoid valve 20 Controllers 23 to 25 Pressure sensor 36 Drain pressure calculation circuit

Claims (5)

A variable displacement hydraulic pump that supplies drive pressure to the hydraulic actuator;
Valve means for generating a control pressure for pump tilt control;
Capacity changing means for changing the pump capacity of the hydraulic pump according to the driving of the valve means;
Command pressure output means for outputting a command pressure for driving the valve means;
Back pressure acquisition means for acquiring back pressure acting on the valve means against the command pressure;
A pump tilt control device for a hydraulic working machine, comprising: correction means for correcting the command pressure according to the back pressure acquired by the back pressure acquisition means. The pump tilt control device for a hydraulic working machine according to claim 1,
The command pressure output means includes
A pilot hydraulic pump for generating pilot pressure;
Input means for inputting the target pump tilt;
A pump tilt control device for a hydraulic working machine, comprising: a pressure reducing means for reducing a pilot pressure from the pilot hydraulic pump in accordance with a target pump tilt. The pump tilt control device for a hydraulic working machine according to claim 1 or 2,
The back pressure acquisition means includes
A discharge pressure detecting means for detecting a discharge pressure of the hydraulic pump;
Storage means for storing the relationship between pump discharge pressure and back pressure in advance;
A hydraulic working machine pump comprising back pressure calculating means for calculating a back pressure based on the relationship between the discharge pressure detected by the discharge pressure detecting means and the stored pump discharge pressure and back pressure. Tilt control device. The pump tilt control device for a hydraulic working machine according to claim 1 or 2,
The back pressure acquisition means includes back pressure detection means for detecting back pressure. The pump tilt control device for a hydraulic working machine according to any one of claims 1 to 4,
Command pressure detecting means for detecting command pressure acting on the valve means;
And a control means for controlling the command pressure output means so that the command pressure detected by the command pressure detection means becomes the command pressure corrected by the correction means. Roll control device.

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