JP6389384B2 - Hydraulic drive system - Google Patents

Description

  The present invention relates to a hydraulic drive system capable of controlling the discharge capacity of a variable displacement hydraulic pump that is driven by an engine to discharge pressurized liquid.

  A construction machine or the like includes a hydraulic pump that is rotationally driven by an engine. When an operation tool such as an operation lever is operated, pressure oil is discharged from the hydraulic pump. The discharged pressure oil is guided to a hydraulic actuator such as a hydraulic cylinder. Accordingly, the hydraulic actuator is operated, and the arm, the boom, and the like are moved by the operation of the hydraulic actuator. On the other hand, when the hydraulic actuator is operated with the pressure oil from the hydraulic pump, the load on the engine increases and the engine speed decreases. As a device for suppressing such a decrease in engine speed, for example, a discharge amount control device disclosed in Patent Document 1 is known.

  In the discharge amount control device of Patent Document 1, a set reference rotational speed is set, and when the actual engine speed falls below the set reference rotational speed, the rotational speed deviation between the set reference rotational speed and the actual engine speed. Accordingly, the pump absorption torque (i.e., the discharge flow rate) is lowered to reduce the engine load.

Japanese Patent Publication No. 6-58111

  In the discharge amount control device of Patent Document 1, the pump absorption torque is not reduced unless the actual engine speed is less than the set reference engine speed. If the engine speed decreases rapidly due to the load on the hydraulic pump, that is, if the deceleration of the actual engine speed is large, unless the engine load condition is improved, it is necessary to Can be predicted. However, even in such a case, the pump absorption torque is not reduced until it falls below the set reference rotation speed, so that the drop in the actual rotation speed after falling below the set reference rotation speed becomes large.

  Therefore, an object of the present invention is to provide a hydraulic drive system that can prevent the engine speed from excessively decreasing.

  The hydraulic drive system according to the present invention includes a variable displacement hydraulic pump that is driven to rotate by an engine to discharge pressurized liquid, and a capacity that adjusts a pump flow rate of the hydraulic pump by switching a discharge capacity of the hydraulic pump. A variable mechanism, a rotation speed sensor for detecting the actual rotation speed of the engine, and a control for controlling the movement of the displacement variable mechanism so as to control the discharge capacity of the hydraulic pump to a predetermined target discharge capacity The controller calculates a deceleration of the actual rotational speed based on the actual rotational speed detected by the rotational speed sensor, and starts a control in which the deceleration of the actual rotational speed is predetermined. When it becomes less than the threshold value, the movement of the variable capacity mechanism is controlled so that the pump output of the hydraulic pump is lower than the target output.

  According to the present invention, since the pump output of the hydraulic pump is reduced based on the deceleration of the actual rotational speed, before the drop in speed is relatively large (that is, the absolute value of deceleration is relatively large). In addition, the pump output of the hydraulic pump can be suppressed (the pump flow rate can be reduced). That is, since the pump output is reduced by predicting in advance that the actual rotational speed falls, it is possible to prevent the actual rotational speed from excessively decreasing.

  In the above invention, the control device calculates a reduction amount that is an output to be reduced with respect to the target output and increases in accordance with the deceleration of the actual rotational speed, and reduces the reduction amount from the target output. The movement of the variable capacity mechanism may be controlled so that the pump output of the hydraulic pump is output to the corrected pump output.

  According to the above configuration, the amount of reduction increases as the deceleration of the actual rotational speed is large, that is, as the actual rotational speed decreases rapidly. Thereby, the engine load can be reduced in accordance with the deceleration of the actual rotational speed, and the engine can be prevented from dropping excessively.

  In the above invention, the engine is controlled to rotate at a predetermined target rotational speed, and the controller is configured to reduce the reduction amount when the actual rotational speed is equal to or higher than the target rotational speed. May be set to zero.

  If the said structure is followed, when the load concerning an engine will reduce rapidly etc. and an actual rotation speed becomes more than a target rotation speed, the fall of the deceleration of an actual rotation speed will not be suppressed. Thereby, the output fall when the load concerning an engine is light can be prevented.

  In the above invention, the engine is controlled so as to be driven to rotate at a predetermined target rotational speed, and the controller is configured to reduce the amount of reduction when the actual rotational speed is less than the target rotational speed. May be increased in accordance with the amount of decrease in the actual rotational speed.

  According to the above configuration, it is possible to reduce the amount of reduction when the actual rotational speed is near the target rotational speed. As a result, it is possible to promote a decrease in the actual rotational speed in the vicinity of the target rotational speed, and promote an increase in the output of the engine E accompanying the decrease in the actual rotational speed.

  In the above invention, the control device calculates a first reduction amount that is an output to be reduced with respect to the target output, based on a rotational speed difference that is a difference between a preset rotational speed set in advance and the actual rotational speed. When the second reduction amount, which is the output that should be reduced with respect to the target output and increases in accordance with the deceleration of the actual rotational speed, is smaller than the first reduction amount, The output to be reduced may be changed from the second reduction amount to the first reduction amount.

  According to the above configuration, even when the decrease in the actual rotational speed is moderate, the actual rotational speed can be returned to the set rotational speed by falling below the set rotational speed.

  In the above invention, the control start threshold value may be set such that a dead zone is generated in which the control device does not lower the pump output of the hydraulic pump below the target output even when the actual rotational speed decreases.

  If the said structure is followed, when the fall of an actual rotation speed is moderate, the fall of the pump output of a hydraulic pump can be suppressed.

  ADVANTAGE OF THE INVENTION According to this invention, it can prevent that the rotation speed of an engine falls too much.

It is a block diagram which shows the hydraulic drive system which concerns on 1st thru | or 3rd embodiment of this invention. It is a circuit diagram which shows the outline of a structure of the tilt angle adjustment apparatus of a hydraulic drive system. It is the functional block diagram which made the block the function which the control apparatus with which the hydraulic drive system of 1st Embodiment has was shown. It is a flowchart which shows the procedure of the rotation speed fall suppression process which the control apparatus of FIG. 3 performs. It is a flowchart which shows the procedure of the ESS control calculation process in the rotation speed fall suppression process of FIG. It is a flowchart which shows the procedure of the DSS control calculation process in the rotation speed fall suppression process of FIG. FIG. 5 is a graph showing a change over time in the engine speed when the engine speed reduction suppressing process of FIG. 4 is executed. FIG. It is the functional block diagram which showed the function which the control apparatus with which the hydraulic drive system of 2nd Embodiment has was made into a block. It is a flowchart which shows the procedure of the DSS control calculation process in the rotation speed fall suppression process of 2nd Embodiment. It is the functional block diagram which showed the function which the control apparatus with which the hydraulic drive system of 3rd Embodiment has was shown as a block. It is a graph which shows the torque diagram regarding the relationship between an engine output torque and an actual rotation speed.

  Hereinafter, hydraulic drive systems 1, 1A, and 1B according to first to third embodiments of the present invention will be described with reference to the drawings. In addition, the concept of the direction used in the following description is used for convenience in description, and does not limit the direction of the configuration of the invention in that direction. Moreover, the hydraulic drive systems 1, 1A, 1B described below are only one embodiment of the present invention. Therefore, the present invention is not limited to the embodiments, and additions, deletions, and changes can be made without departing from the spirit of the invention.

[First Embodiment]
A construction machine includes various attachments such as a bucket, a loader, a blade, and a hoisting machine, and is moved by a hydraulic actuator such as a hydraulic cylinder or a hydraulic motor (electric oil motor). For example, a hydraulic excavator that is a kind of construction machine includes a bucket, an arm, and a boom, and can perform operations such as excavation while moving these three members. Each of the bucket, arm, and boom is provided with hydraulic cylinders 11-13, and the bucket, arm, and boom are moved by supplying pressure oil to each cylinder 11-13.

  Moreover, the hydraulic excavator has a traveling device, and a revolving body is mounted on the traveling device so as to be capable of turning. A boom is attached to the revolving structure so as to be swingable in the vertical direction. A hydraulic turning motor 14 is attached to the turning body, and the turning body is turned by supplying pressure oil to the turning motor 14. Further, the traveling device is provided with a hydraulic traveling motor 15 (left traveling motor 15L and right traveling motor 15R) so that the traveling motor 15 is moved forward or backward by supplying pressure oil. It has become.

  The hydraulic excavator is provided with an operation valve 19 described later in association with each of the hydraulic actuators 11 to 15. FIG. 1 shows only one operation valve 19. A hydraulic pressure supply device 16 is connected to the hydraulic actuators 11 to 15 (that is, the hydraulic cylinders 11 to 13 and the hydraulic motors 14 and 15). When any one of the operation tools of the plurality of operation valves 19 is operated, pressure oil is supplied from the hydraulic pressure supply device 16 to the hydraulic actuators 11 to 15 associated with the operation valve 19, and the associated hydraulic actuator 11. ~ 15 are activated.

  More specifically, the hydraulic pressure supply device 16 includes two hydraulic pumps 17L and 17R, a hydraulic control valve 18, a plurality of operation valves 19, and two tilt angle adjusting devices 20. The two hydraulic pumps 17L and 17R share one rotating shaft 17a, and discharge the pressure oil by rotating the rotating shaft 17a. The pressure oil discharged from the hydraulic pumps 17L and 17R is guided to the hydraulic control valve 18. A plurality of operation valves 19 are connected to the hydraulic control valve 18. The operation valve 19 has an operation tool (operation lever or the like) (not shown), and when any of the operation levers of the plurality of operation valves 19 is operated, the hydraulic actuators 11 to 15 corresponding to the operated operation tool. The flow of the pressure oil is controlled so as to flow the pressure oil.

  When the operation tool is operated, each operation valve 19 outputs pilot oil having a pressure corresponding to the operation amount (for example, the tilt amount) of the operation tool in a direction corresponding to the operation direction (for example, the tilt direction) of the operation tool. It is supposed to be. The output pilot oil is guided to the hydraulic control valve 18, and the hydraulic control valve 18 controls the flow of the pressure oil discharged from the hydraulic pumps 17L and 17R according to the output pilot oil. In other words, the hydraulic control valve 18 is configured to flow pressure oil to the hydraulic actuators 11 to 15 corresponding to the operation tool to be operated to operate them. Further, the hydraulic control valve 18 supplies pressure oil having a flow rate corresponding to the pilot pressure output from the operation tool to the corresponding hydraulic actuators 11 to 15, and the hydraulic actuators 11 to 15 at a speed corresponding to the operation amount of the operation tool. Is to move. In this way, the bucket, arm, boom, and the like can be moved at a speed corresponding to the operation amount of the operation tool.

  In the hydraulic pressure supply device 16 configured as described above, variable displacement pumps are employed as the hydraulic pumps 17L and 17R, and in this embodiment, variable displacement swash plate pumps are employed. Since the hydraulic pumps 17L and 17R have the same configuration, only the configuration of one hydraulic pump 17L will be described, and the description of the configuration of the other hydraulic pump 17R will be omitted.

The hydraulic pump 17L has a swash plate 17b, and the discharge capacity can be changed by changing the tilt angle. The hydraulic pump 17 has a tilt angle to change the tilt angle of the swash plate 17b. An adjusting device 20 is provided. The tilt angle adjusting device 20 includes a power shift valve 20a and a servo mechanism 20b. The power shift valve 20a is an electromagnetic proportional valve, for example, and is connected to a pilot pump (not shown). Power shift valve 20a is adapted to output a power shift pressure p ₁ in accordance with the power shift command (the maximum output command) output from the controller 30 to be described later. The power shift valve 20a is connected to the servo mechanism 20b, and the output drive oil is guided to the servo mechanism 20b.

The servo mechanism 20b has a servo piston (not shown). A swash plate 17b is connected to the servo piston, and the tilt angle of the swash plate 17b can be changed by moving the servo piston. Servo piston is adapted to limit the maximum pump output according to the power shift pressure p _1. That is, the tilting angle of the swash plate 17b is adapted to be adjusted in accordance with the power shift pressure p _1. In the present embodiment, the servo mechanism 20b, when the power shift pressure p ₁ increases to reduce the tilting angle of the swash plate 17b, so power shift pressure p ₁ is to increase the tilt angle of the small becomes the swash plate 17b ing. Thus, the tilt angle adjusting device 20 adjusts the tilt angle to control the discharge capacity of the hydraulic pump 17L, thereby adjusting the pump torque of the hydraulic pump 17L.

The hydraulic pressure supply device 16 constitutes a negative control type hydraulic system, and outputs a negative control pressure to the tilt angle adjusting device 20. The servo mechanism 20b, which is an angle corresponding to one higher pressure of the negative control pressure and power shift pressure p ₁ to adjust the tilting angle of the swash plate 17b. In this configuration, so that it limits the hydraulic pump 17L, the maximum discharge capacity of the 17R (i.e., the maximum pump flow rate) by the power shift pressure p _1. An engine E is provided on the rotary shaft 17a of the hydraulic pumps 17L and 17R configured as described above.

  The engine E is configured to rotationally drive the rotary shafts 17a of the hydraulic pumps 17L and 17R. In the present embodiment, a diesel engine is employed as the engine E, and the engine E has an engine speed control device 21. The engine speed control device 21 is a so-called mechanical governor, to which an accelerator opening degree command is input. The engine speed control device 21 adjusts the fuel injection amount of the engine E according to the droop characteristic. An ECU may be used as the rotation speed control device 21. At this time, the fuel injection amount of the fuel injection device is electronically controlled by the ECU so that the rotational speed of the rotary shaft 17a is adjusted to the set rotational speed command value. The engine E is not necessarily a diesel engine, and may be a gasoline engine.

  A rotation speed sensor 22 is attached to the rotation shaft 17a, and the rotation speed sensor 22 outputs a signal corresponding to the rotation speed of the rotation shaft 17a. The rotation speed sensor 22 is electrically connected to the control device 30, and the control device 30 calculates the actual rotation speed of the engine E, that is, the actual rotation speed, based on the signal from the rotation speed sensor 22. ing. In the case of the electronic control type, the control device 30 is communicably connected to the ECU by communication means such as CAN communication, and receives signals from the ECU. Further, an accelerator dial 24 and a mode input device 25 are connected to the control device 30 via communication means using CAN communication or the like.

  The accelerator dial 24 is a dial type rotation speed setting device for setting the rank of the set rotation speed. The accelerator dial 24 outputs a signal corresponding to the scale adjusted by the driver to the control device 30. The mode input device 25 is a device for inputting a mode, and is an input means constituted by, for example, a panel. The mode input device 25 is configured to output a command input by the driver via the input means to the control device 30 as a CAN signal.

The controller 30 has a target speed calculation map, the target rotation speed calculation map is associated with the signal target rotational speed N _t is outputted from the accelerator dial 24 and the mode input device 25. Controller 30, and calculates the target rotational speed N _t based on the two signals are respectively output from the accelerator dial 24 and the mode input unit 25 using the target rotational speed calculation map. Further, the control unit 30, the accelerator opening command corresponding to the calculated target rotation speed N _t to output to the engine speed control device 21, to control the fuel injection amount of the engine E by the engine speed control device 21 It has become.

  The control device 30 configured as described above outputs a power shift command to the power shift valve 20a of the tilt angle adjusting device 20 to adjust the pump output of the swash plate 17b of the hydraulic pumps 17L and 17R. ing. The control device 30 has a functional part for calculating various values as shown in FIG. 3 to output a power shift command, and calculates various values at predetermined intervals. In the following, each functional part for calculating various values will be described in blocks.

The control device 30 includes an engine speed sensing control block (abbreviation: ESS control block) 31, a transient characteristic speed sensing control block (abbreviation: DSS control block) 32, a reduction amount selection unit 33, and a power shift amount setting unit 34. The power shift amount correcting unit 35 and the power shift command output unit 36 are provided. When the actual rotational speed N of the engine E becomes less than a preset rotational speed N _set , the ESS control block 31 is based on a rotational speed difference that is a difference between the set rotational speed N _set and the actual rotational speed N. The power shift amounts of 17L and 17R are controlled (that is, ESS controlled). In the present embodiment, the ESS control block 31 calculates a first reduction amount that is a power shift amount to be reduced in order to perform PID control of the power shift amount of the hydraulic pumps 17L and 17R based on the rotational speed difference. ing. Note that the ESS control executed in the ESS control block 31 is not necessarily PID control, and may be PI control or PD control. Hereinafter, the configuration of the ESS control block 31 will be described in more detail.

The ESS control block 31 includes a set rotation speed calculation unit 41, a rotation speed difference calculation unit 42, a PID control unit 43, and a first lower limit limiting unit 44. The set rotational speed calculation unit 41 determines a rank based on a signal from the accelerator dial 24 and determines a mode based on a signal from the mode input device 25. Further, the set rotation speed calculation unit 41 has a set rotation speed calculation map 41a as shown in FIG. 3, and in the set rotation speed calculation map 41a, the set rotation speed N _set is associated with the rank and mode. ing. The set rotation speed calculation unit 41 calculates a set rotation speed N _set based on the determined rank and mode by using the set rotation speed calculation map 41a. The calculated set rotational speed N _set is used by the rotational speed difference calculation unit 42.

The rotation speed difference calculation unit 42 calculates a rotation speed difference that is a difference between the set rotation speed N _set and the actual rotation speed N. More specifically, the rotation speed difference calculation unit 42 calculates a rotation speed difference obtained by subtracting the actual rotation speed N from the set rotation speed N _set . The calculated rotational speed difference is used by the PID control unit 43. The PID control unit 43 uses a PID control control arithmetic expression to calculate a first reduction amount that is a power shift amount that should be reduced to bring the actual rotational speed N closer to the set rotational speed N _set based on the rotational speed difference. Is calculated. In the PID control unit 43 of the present embodiment, when the actual rotational speed N is equal to or higher than the set rotational speed N _set , the first reduction amount is calculated as a negative value so as to increase the power shift amount of the hydraulic pumps 17L and 17R. Is done.

The first lower limit limiting unit 44 is a limiter for preventing the ESS control from being executed when the actual rotational speed N is equal to or greater than the set rotational speed N _set , and is the first when the first reduction amount is less than zero. The amount of reduction is set to zero (see the graph of the first lower limit limiting unit 44 in FIG. 3). In addition, when the 1st increase / decrease amount is zero or more, the 1st minimum limit part 44 makes 1st reduction amount a value as it is. As described above, the first lower limit limiting unit 44 is configured to limit the lower limit value of the first reduction amount. The limited first reduction amount is used by the reduction amount selection unit 33 together with the second reduction amount. The second reduction amount is calculated by the DSS control block 32.

The DSS control block 32 controls the pump output of the hydraulic pumps 17L and 17R, that is, performs DSS control when the deceleration of the actual rotational speed N of the engine E becomes less than a predetermined value. In the present embodiment, when the differential value ΔN of the actual rotational speed N becomes less than a predetermined differential value ΔN _set (control start threshold position), the DSS control block 32 determines the hydraulic pump based on the differential value ΔN. The pump outputs of 17L and 17R are controlled. More specifically, the DSS control block 32 calculates the second reduction amount to control the pump outputs of the hydraulic pumps 17L and 17R based on the differential value ΔN of the actual rotational speed N. The second reduction amount is a power shift amount that should be reduced in order to prevent a sudden drop in the actual rotational speed N. Hereinafter, the configuration of the DSS control block 32 will be described in more detail.

  The DSS control block 32 includes a filter unit 51, a differential calculation unit 52, a dead zone setting unit 53, a reference reduction amount calculation unit 54, and a second lower limit limiting unit 57. The filter unit 51 is a so-called low-pass filter, and gradually reduces (that is, filters) a high-frequency component of the actual engine speed N of the engine E calculated based on a signal from the engine speed sensor 22. The filter unit 51 does not necessarily need to gradually decrease the high frequency component of the actual rotational speed N, and may decrease the high frequency component of the differential value ΔN of the actual rotational speed N that is calculated later. The reduced actual rotational speed N is used in the differential operation unit 52. The differential calculation unit 52 calculates a deceleration of the actual rotation number N, that is, a differential value ΔN of the actual rotation number N based on the actual rotation number N calculated by the filter unit 51. The calculated differential value ΔN of the actual rotational speed N is used by the dead zone setting unit 53.

The dead zone setting unit 53 has a filtering function, and the differential value ΔN of the actual rotational speed N is calculated like a ramp function. More specifically, the dead zone setting unit 53 sets the differential value ΔN of the actual rotational speed N to zero when the differential value ΔN of the actual rotational speed N is greater than or equal to a predetermined differential value ΔN _set . (Refer to the graph in the block of the dead zone setting unit 53 in FIG. 3). On the other hand, when the differential value ΔN of the actual rotational speed N is less than the set differential value ΔN _set , the dead zone setting unit 53 subtracts the differential value ΔN that is a value obtained by subtracting the set differential value ΔN _set from the differential value ΔN of the actual rotational speed N. -ΔN _set is calculated. The dead zone setting unit 53 sets the differential value ΔN to zero when the differential value ΔN of the actual rotational speed N is equal to or larger than the set differential value ΔN _set in this way, and the differential value ΔN of the actual rotational speed N is equal to or larger than the set differential value ΔN _set. The dead zone is set in the area. Thus, the dead zone setting unit 53 performs filtering on the differential value ΔN, and the filtered differential value ΔN _fill is used by the reference reduction amount calculation unit 54. The reference reduction amount calculation unit 54 calculates a reference reduction amount obtained by multiplying the differential value ΔN _file filtered by the dead zone setting unit 53 by a predetermined gain. In the present embodiment, the gain is set to a negative value, and the calculated reference reduction amount is a positive value.

  The second lower limit limiting unit 57 is a limiter for preventing the DSS control from being executed when the reference reduction amount is less than zero (that is, when the calculation result is such that the pump flow rate is increased). The second lower limit limiting unit 57 sets the reference reduction amount to zero when the reference reduction amount is less than zero (see the graph of the second lower limit limiting unit 57 in FIG. 3). When the reference increase / decrease flow rate is zero or more, the second lower limit restricting unit 57 sets the second reduction amount as the value of the reference reduction amount. Thus, the second lower limit restricting unit 57 is configured to restrict the lower limit value of the reference reduction amount. The limited reference reduction amount is used by the reduction amount selection unit 33 together with the first reduction amount calculated by the ESS control block 31 as the second reduction amount.

  The reduction amount selection unit 33 compares the first reduction amount and the second reduction amount, and selects the one with the larger reduction amount. The selected reduction amount, which is the selected reduction amount, is used by the power shift amount correction unit 35 together with the target power shift amount calculated by the power shift amount setting unit 34. The power shift amount setting unit 34 calculates a target power shift amount based on a rank and a mode determined based on signals from the accelerator dial 24 and the mode input device 25, respectively. More specifically, the power shift amount setting unit 34 has a power shift amount calculation map, and the target power shift amount is associated with the rank and mode in the power shift amount calculation map. The power shift amount setting unit 34 calculates the target power shift amount based on the determined rank and mode by using the power shift amount calculation map. The calculated target power shift amount is used by the power shift amount correction unit 35 together with the selection reduction amount selected by the reduction amount selection unit 33.

The power shift amount correction unit 35 calculates a correction power shift amount based on the target power shift amount and the selection reduction amount. More specifically, the power shift amount correction unit 35 calculates the correction power shift amount by subtracting the selection reduction amount from the target power shift amount. The correction power shift amount calculated in this way is such that the first reduction amount is the second reduction amount as in the case where the decrease in the actual rotation speed N is gradual and the actual rotation speed N is equal to or less than the set rotation speed N _set. When larger, the value is obtained by subtracting the first reduction amount from the target power shift amount. On the other hand, when the first reduction amount is smaller than the second reduction amount, such as when the actual rotational speed N decreases rapidly, the correction power shift amount is a value obtained by subtracting the second reduction amount from the target power shift amount. . The power shift command output unit 36 outputs a power shift command, which is a current command corresponding to the corrected power shift amount, to the power shift valve 20a so that the power shift amount of the hydraulic pumps 17L and 17R becomes the calculated corrected power shift amount. The movement of the power shift valve 20a is controlled.

  In the hydraulic drive system 1 having such a configuration, when the load on the hydraulic pumps 17L and 17R increases and the rotational speed of the engine E decreases, the swash plate 17b tilts to suppress the pump output of the hydraulic pumps 17L and 17R. The corner is adjusted. Hereinafter, FIGS. 4 to 6 will be described with reference to FIGS. 4 to 6 regarding the processing of the rotational speed reduction suppression control (that is, the rotational reduction suppression processing) of the control device 30 when any of the operating tools is operated and the load on the hydraulic pumps 17L and 17R increases. The description will be given with reference. In the hydraulic drive system 1, when the engine E is driven, the control device 30 starts the rotation reduction suppressing process and proceeds to step S1.

In the set rotation speed calculation step that is step S1, first, the set rotation speed calculation unit 41 of the ESS control block 31 determines the rank and mode based on signals from the accelerator dial 24 and the mode input device 25. Next, the set rotation speed calculation unit 41 calculates the set rotation speed N _set based on the determined rank and mode. When the set rotation speed N _set is calculated, the process proceeds to step S2 and step S3. In the ESS control calculation process which is Step S2, ESS control calculation processing is executed to control the pump output of the hydraulic pumps 17L and 17R based on the rotation speed difference which is the difference between the actual rotation speed N and the set rotation speed N _set. Then, the first reduction amount is calculated. On the other hand, in the DSS control calculation step, which is Step S3, the DSS control calculation process is executed to control the pump output based on the differential value of the actual rotation speed N (that is, the deceleration of the actual rotation speed), and the second reduction. The quantity is calculated. Hereinafter, the details of the ESS control calculation process executed in the ESS control calculation process will be described with reference to FIG.

In the ESS control calculation process, when the process starts, the process proceeds to step S11. In the rotation speed difference calculation step that is step S11, the rotation speed difference calculation unit 42 calculates the rotation speed difference based on the actual rotation speed N and the set rotation speed N _set . When the rotation speed difference is calculated, the process proceeds to step S12. In the first reduction amount calculation step that is step S12, the PID control unit 43 calculates the first reduction amount based on the rotation speed difference calculated by the rotation speed difference calculation unit. When the first reduction amount is calculated, the process proceeds from step S12 to step S13. In the first lower limit limiting step that is Step S13, when the first reduction amount is less than zero (that is, when the actual rotational speed N is equal to or greater than the set rotational speed N _set ), the first lower limit limiting unit 44 performs the first reduction. Set the amount to zero. On the other hand, when the first reduction amount is equal to or greater than zero (that is, when the actual rotation speed N is less than the set rotation speed N _set ), the first lower limit limiting unit 44 sets the first reduction amount as it is. Thus, in the first lower limit limiting step, the first reduction amount is limited so that the first reduction amount does not become a value less than zero. As a result, the ESS control is not executed when the actual rotational speed N is equal to or greater than the set rotational speed _Nset . When the lower limit of the first reduction amount is performed, the ESS control calculation process ends. Next, the details of the DSS control calculation process executed in the DSS control calculation step, which is step S3, will be described with reference to FIG.

  In the DSS control calculation process, when the process starts, the process proceeds to step S21. In the filtering step that is Step S21, the filter unit 51 gradually reduces the high-frequency component of the actual rotational speed N. When it is decreased, the process proceeds to step S22. In the differential value calculation step that is step S22, the differential calculation unit 52 calculates the differential value ΔN based on the reduced actual rotational speed N. When the differential value ΔN is calculated, the process proceeds to step S23.

In the dead zone setting step, which is step S23, the dead zone setting section 53 performs the dead zone setting section 53 in a region where the differential value ΔN is equal to or larger than a predetermined differential value ΔN _set (that is, when the actual rotational speed N increases or gently decreases). The differential value ΔN is set to zero. On the other hand, in a region where the differential value ΔN is less than a predetermined set differential value ΔN _set (that is, when the actual rotational speed N is rapidly decreasing), the dead zone setting unit 53 calculates the set differential value ΔN _set from the differential value ΔN. A subtracted differential value ΔN−ΔN _set which is a subtracted value is calculated. As described above, in the dead zone setting step, the differential value ΔN is set to zero when the actual rotational speed N increases or decreases slowly, and the pump outputs of the hydraulic pumps 17L and 17R are not increased or decreased unnecessarily. When the differential value ΔN is filtered, the process proceeds to step S24. The reference reduction amount calculating step is a step S24, by multiplying a predetermined gain to the filtered differential value .DELTA.N _fil in step S23 to calculate the reference reduction amount. When the reference reduction amount is calculated, the process proceeds to step S25.

  In the second lower limit restricting step, which is Step S25, when the second reduction amount is less than zero, the second lower limit restricting unit 57 sets the second reduction amount to zero. On the other hand, when the second reduction amount is zero or more, the second lower limit restricting unit 57 sets the second reduction amount as the reference reduction amount. When the lower limit of the second reduction amount is performed, the DSS control calculation process ends. When the DSS control calculation process is completed together with the ESS control calculation process, the process proceeds from step S2 and step S3 to step S4. Hereinafter, returning to FIG. 4 again, the procedure after step S4 will be described.

  In the reduction amount selection step that is step S4, the calculated first reduction amount and second reduction amount are compared, and the larger reduction amount is selected as the selection reduction amount. When the selection reduction amount is determined, the process proceeds to step S5. In the pump output determination step that is step S5, the power shift amount setting unit 34 calculates the target power shift amount based on the rank and mode determined in step S1 by using the pump output calculation map. Next, the power shift amount correction unit 35 calculates the corrected power shift amount by subtracting the selection reduction amount from the calculated target power shift amount. The corrected power shift amount calculated in this way is determined as the power shift amount of the hydraulic pumps 17L and 17R, and the process proceeds to step S6. In the power shift amount reduction process, which is step S6, the power shift command output unit 36 outputs a power shift command corresponding to the corrected power shift amount to the power shift valve 20a, and corrects the power shift amount of the hydraulic pumps 17L and 17R. Adjust to the amount. When the power shift amount of the hydraulic pumps 17L and 17R is adjusted to the correction power shift amount, the process returns to step S1. Thereby, the adjustment of the power shift amount of the hydraulic pumps 17L and 17R is repeatedly performed.

  Thus, in the rotational speed reduction suppression control of the hydraulic drive system 1, when the actual rotational speed N of the engine E decreases, the power shift amount of the hydraulic pumps 17L and 17R is reduced to the power shift amount obtained by subtracting the selected reduction amount from the target power shift amount. To suppress a decrease in the actual rotational speed N. Thereby, even if the operating tool is operated and the load on the engine E increases, it is possible to prevent the actual rotational speed N from dropping excessively. Thereby, the fluctuation | variation of the actual rotation speed N can be suppressed, and the fuel consumption of the engine E can be improved. Hereinafter, the effect of suppressing the decrease in the actual rotational speed N by the rotational speed decrease suppression control when the operation tool is operated to increase the load on the hydraulic pumps 17L and 17R will be described with reference to the graph of FIG. The graph of FIG. 7 shows a change with time of the actual rotational speed N of the engine E when any of the operation tools is operated and the load on the hydraulic pumps 17L and 17R increases. In FIG. 7, the vertical axis indicates the actual rotational speed N, and the horizontal axis indicates time t. Also, the solid line in FIG. 7 is a form in which both ESS control and DSS control can be performed, that is, a change with time of the actual rotational speed N of the hydraulic pump drive system 1 of the present embodiment. On the other hand, the alternate long and two short dashes line in FIG. 7 shows a case where only the ESS control can be executed, that is, a change with time of the actual rotational speed N of the hydraulic pump drive system of the prior art.

In the hydraulic pump drive system 1, in a state where the operation member is not operated and the engine E is rotated at the target rotation speed N _t, it decreases the actual rotational speed N the load increases the operating tool is operated by the engine E (Time t1). Although the actual rotational speed N starts to decrease, the ESS control is not executed because it is greater than the set rotational speed N _set determined based on the rank and mode. However, the second reduction amount increases in the DSS control process. As a result, the drop in the actual rotational speed N is reduced after time t11 compared to the hydraulic pump drive system of the prior art. Thereafter, both the hydraulic pump drive system 1 and the prior art hydraulic pump drive system continue to decrease in the actual rotational speed N, and eventually falls below the set rotational speed N _{set in the} prior art hydraulic pump drive system (see time t12). If it does so, in the hydraulic pump drive system of a prior art, ESS control will be performed and the fall of the actual rotation speed N will be relieved. On the other hand, the hydraulic pump drive system 1, the actual rotational speed N is maintained above the set rotational speed N _set by the DSS control.

When the time further elapses, the actual rotational speed N of the hydraulic pump drive system 1 eventually decreases below the set rotational speed N _set (see time t2). Then, either ESS control or DSS control is executed according to the magnitude of the reduction amount, but since the drop in the actual rotational speed N is mitigated by the DSS control, the actual rotational speed N is set to the set rotational speed N _set. Even if it becomes below, it is maintained near the set rotational speed _Nset . In this way, by using DSS control, it is possible to suppress the actual rotational speed from drastically dropping with respect to the set rotational speed N _set as in the conventional hydraulic pump drive system, and the actual rotational speed N is excessively large. It can suppress that it falls.

After that, when the operating tool is returned to the original position, that is, the neutral position (see time t3), so-called load loss of the engine E occurs. Thus, the load of the engine E is reduced, the actual rotational speed N is gradually restored to the target rotation speed N _t. At this time, the differential value ΔN of the actual rotational speed N becomes a positive value, but a region where the differential value ΔN becomes a positive value is set as a dead zone by the dead zone setting unit 53. Therefore, never hydraulic pump 17L, pump output 17R is corrected, that is, never to extra compensation, it is possible to restore the actual rotational speed N to quickly target rotational speed N _t.

Since the hydraulic drive system 1 configured in this way changes the amount of reduction from the target power shift amount according to the deceleration of the actual rotational speed N by DSS control, the drop in speed is relatively large (that is, hydraulic pump 17L before the absolute value of the deceleration is relatively larger) What the actual rotational speed N falls below the set rotational speed N _{the set,} it is possible to reduce the pump output 17R. That is, since the pump output is reduced by predicting in advance that the actual rotational speed N of the engine E will be low, it is possible to prevent the actual rotational speed N from excessively decreasing. Further, in the hydraulic drive system 1, even if the DSS control is not executed when the actual rotational speed N decreases gradually, ESS control is executed becomes below the set rotational speed N _{The set.} Therefore, it is possible to prevent the actual rotational speed N from dropping excessively with respect to the set rotational speed N _set .

[Second Embodiment]
The hydraulic drive system 1A of the second embodiment is similar in configuration to the hydraulic drive system 1 of the first embodiment. Below, about the hydraulic pump drive system 1A, only a different structure from the structure of the hydraulic pump drive system 1 of 1st Embodiment is demonstrated, and description is abbreviate | omitted about the same structure. The same applies to the hydraulic drive system 1B of the third embodiment.

  In the hydraulic drive system 1A of the second embodiment, as shown in FIG. 8, the DSS control block 32A of the control device 30A corrects the reference power shift amount calculated by the reference reduction amount calculation unit 54 with the correction coefficient k. The second reference limit 57 is used to filter the reference reduction amount. The DSS control block 32 </ b> A having such a function includes a correction coefficient calculation unit 55 and a reduction amount correction unit 56.

The correction coefficient calculation unit 55 calculates a correction coefficient for correcting the reference reduction amount separately from the reference reduction amount calculated by the reference reduction amount calculation unit 54. More specifically, the correction coefficient calculation unit 55 has a correction coefficient calculation map. In the correction coefficient calculation map, the actual rotation speed N of the engine E and the correction coefficient k are corrected coefficient calculation unit 55 in FIG. Corresponding as in the graph in the block. That is, in the correction coefficient calculation map, when the actual rotation speed N is less than the limit start rotation speed N _lim , the correction coefficient k is predetermined A1 (A1 = 1 in the present embodiment). The limit start rotation speed N _lim is a value obtained by offsetting a predetermined offset value N _of to the set rotation speed N _set . When the actual rotational speed N is equal to or higher than the limit starting rotational speed N _{lim and} less than the target rotational speed N _t , the correction coefficient k decreases linearly according to the actual rotational speed N. In the present embodiment, the actual rotation speed N is the limit start rotation speed N _lim and the correction coefficient k is the first parameter A1 (A1 = 1 in the present embodiment), and the actual rotation speed N is the target rotation speed N _t and the correction coefficient. Is linearly decreased so that the second parameter A2 becomes A2 (A2 = 0 in the present embodiment). Note that the manner in which the correction coefficient k decreases when the actual rotational speed N is greater than or equal to the limit start rotational speed N _{lim and} less than the target rotational speed N _t is not necessarily linear but may be curvilinear. You may make it have a primary delay. Further, in the correction coefficient calculation map, when the actual rotation speed N is _{equal to} or greater than the target rotation speed Nt, the correction coefficient k is A2. The threshold of the actual rotational speed N of the correction coefficient k to A2 is a not necessarily limited to the target rotational speed N _t, the rotational speed offset a predetermined value N _W to limit start rotational speed N _lim Also good. In this case, it is preferable rotational speed offset is equal to or less than the target rotational speed N _t. The correction coefficient calculation unit 55 calculates a limit start rotation number N _lim based on the _set rotation number N _set calculated by the set rotation number calculation unit 41, and calculates a correction coefficient calculation map based on the calculated limit start rotation number N _lim . Set. The correction coefficient calculator 55 calculates the correction coefficient k based on the actual rotational speed N by using the set correction coefficient calculation map. The calculated correction coefficient k is used by the reduction amount correction unit 56 together with the reference reduction amount calculated by the reference reduction amount calculation unit 54.

The reduction amount correction unit 56 calculates the second reduction amount based on the correction coefficient k and the reference reduction amount. More specifically, the reduction amount correction unit 56 corrects the reference reduction amount by the correction coefficient k, that is, calculates the second reduction amount by multiplying the reference reduction amount by the correction coefficient k. The second reduction amount calculated in the present embodiment, becomes zero when the actual rotational speed N is equal to or higher than the target rotational speed N _t, the actual rotational speed N is the hydraulic pump 17L when larger than the target rotation speed N _t, the 17R The power shift amount is prevented from being reduced. Thus, the actual rotational speed N can be lowered quickly to the target rotational speed N _t. On the other hand, if the actual rotation speed N is less than the target rotational speed N _t, the second reduction amount is adapted to the actual rotational speed N and the differential value ΔN increases as decreases. Therefore, the reduction amount correction unit 56 increases the second reduction amount as the actual rotational speed N decreases, thereby preventing the actual rotational speed N from becoming smaller. The calculated second reduction amount is used by the second lower limit limiting unit 57.

The control device 30A corrects the reference reduction amount calculated by the reference reduction amount calculation unit 54 in accordance with the actual rotational speed N of the engine E. Therefore, the hydraulic pump drive system 1, when the actual rotational speed N when the operating tool is lowered operated by the actual rotational speed N is close to the target rotational speed N _t, the correction amount of power shift amount by DSS control is small Become. As a result, the amount of reduction in the para-shift amount immediately after the operation tool is operated can be suppressed, and the pump outputs of the hydraulic pumps 17L and 17R can be quickly increased.

  Further, the control process of the hydraulic drive system 1A of the second embodiment differs from the hydraulic drive system 1 of the first embodiment only in terms of the DSS control calculation process. Hereinafter, DSS control calculation processing of the hydraulic drive system 1A of the second embodiment will be described with reference to FIG.

  In the DSS control calculation process of the second embodiment, when the process starts, the process proceeds to step S21. In the filtering step that is Step S21, the filter unit 51 gradually reduces the high-frequency component of the actual rotational speed N. When it is decreased, the process proceeds to step S22 and step S26. In the differential value calculation step that is step S22, the differential calculation unit 52 calculates the differential value ΔN based on the reduced actual rotational speed N. When the differential value ΔN is calculated, the process proceeds to step S23.

In the dead zone setting step, which is step S23, the dead zone setting section 53 performs the dead zone setting section 53 in a region where the differential value ΔN is equal to or larger than a predetermined differential value ΔN _set (that is, when the actual rotational speed N increases or gently decreases). The differential value ΔN is set to zero. On the other hand, in a region where the differential value ΔN is less than a predetermined set differential value ΔN _set (that is, when the actual rotational speed N is rapidly decreasing), the dead zone setting unit 53 calculates the set differential value ΔN _set from the differential value ΔN. A subtracted differential value ΔN−ΔN _set which is a subtracted value is calculated. As described above, in the dead zone setting step, the differential value ΔN is set to zero when the actual rotational speed N increases or decreases slowly, and the pump outputs of the hydraulic pumps 17L and 17R are not increased or decreased unnecessarily. When the differential value ΔN is filtered, the process proceeds to step S24. The reference reduction amount calculating step is a step S24, by multiplying a predetermined gain to the filtered differential value .DELTA.N _fil in step S23 to calculate the reference reduction amount.

In this way, the reference reduction amount is calculated in steps S22 to S24. In the DSS control calculation process, as described above, the process proceeds from step S21 to step S22 and also to step S26, and step S26 is executed separately from steps S22 to S24. In the correction coefficient calculation step that is step S26, first, the correction coefficient calculation unit 55 calculates the limit start rotation speed N _lim based on the _set rotation speed N _set calculated in step S1. Next, the correction coefficient calculation unit 55 sets a correction coefficient calculation map based on the calculated limit start rotation speed N _lim . Finally, the correction coefficient calculator 55 calculates the correction coefficient k based on the actual rotational speed N by using the set correction coefficient calculation map. When the reference reduction amount and the correction coefficient k are calculated in this way, the process proceeds to step S27.

  The second reduction amount calculation unit in step S27 corrects the reference reduction amount by the correction coefficient k, that is, calculates the second reduction amount by multiplying the reference reduction amount by the correction coefficient k. When the second reduction amount is calculated, the process proceeds to step S25. In the second lower limit restricting step, which is Step S25, when the second reduction amount is less than zero, the second lower limit restricting unit 57 sets the second reduction amount to zero. On the other hand, when the second reduction amount is zero or more, the second lower limit restricting unit 57 sets the second reduction amount as it is. When the lower limit of the second reduction amount is performed, the DSS control calculation process ends. The subsequent processing is the same as the control processing of the first embodiment.

  The hydraulic drive system 1 </ b> A configured as described above has the same effects as the hydraulic drive system 1 of the first embodiment.

[Third Embodiment]
In the hydraulic drive system 1B, as shown in FIG. 10, the control device 30B has an ESS control block 31B, a DSS control block 32B, and a control selection unit 37. The ESS control block 31B includes a set rotation speed calculation unit 41, a rotation speed difference calculation unit 42, a PID control unit 43, and a first lower limit limiting unit 44, and further includes a power shift amount setting unit 34, A reduction amount subtraction unit 35B. The first reduction amount subtraction unit 35B calculates the first correction amount by subtracting the first reduction amount limited by the first lower limit limiting unit 44 from the target power shift amount calculated by the power shift amount setting unit 34. It has become. In this way, the ESS control block 39 calculates the first correction amount to be set for the hydraulic pumps 17L and 17R when the ESS control is executed.

The DSS control block 39 includes a filter unit 51, a differential calculation unit 52, a control switching determination unit 58, and a second reduction amount determination unit 59. The control switching determination unit 58 determines whether or not the differential value ΔN calculated by the differential calculation unit 52 is less than a predetermined differential value ΔN _set . When the differential value ΔN is less than the set differential value ΔN _set , the control switching determination unit 58 calculates an output value of 1 to execute DSS control. On the other hand, when the differential value ΔN is equal to or greater than the set differential value ΔN _set , the control switching determination unit 58 calculates an output value of 0 so as not to execute the DSS control.

In the DSS control block 39, the second reduction amount determination unit 59 determines the second reduction amount based on the actual rotational speed N filtered by the filter unit 51. More specifically, in the second reduction amount determination unit 59, the actual rotational speed N is divided into a plurality of bands (four bands in the present embodiment), and different set flow rates are associated with each band. In the present embodiment, a range where the actual rotational speed N is less than the first rotational speed N1 (N _set > N1) is set as the first band, and the first set flow rate Q1 is associated with the first band. The range where the actual rotation speed N is greater than or equal to the first rotation speed N1 and the second rotation speed N2 (N2> N1) is set as the second band, and the second set flow rate Q2 (Q2 <Q1) is associated with the second band. It has been. Further, the range of the actual rotation speed N is equal to or higher than the second rotation speed N2 and the third rotation speed N3 (N3> N1, N2) is set as the third band, and the third set flow rate Q3 (Q3 <Q3 < Q1, Q2) are associated with each other. A range where the actual rotational speed N is equal to or greater than the third rotational speed N3 is set as the fourth band, and the fourth set flow rate Q4 (Q4 <Q1, Q2, Q3) is associated with the fourth band.

  The first rotation speed N1 is set in advance based on a torque diagram as shown in FIG. The torque diagram in FIG. 11 is a graph showing the relationship between the output torque of the engine E and the actual rotational speed N when the output torque of the engine E and the pump torque of the hydraulic pumps 17L and 17R are balanced. In FIG. 11, the vertical axis represents the output torque, and the horizontal axis represents the rotational speed. The first rotational speed N1 is set near the rotational speed at which the output torque is maximum in the torque diagram of FIG. 11, specifically, slightly larger than the rotational speed. Further, the second rotation speed N2 and the third rotation speed N3 are set with reference to the torque diagram of FIG. 11 so as to divide the region where the rotation speed is larger than the first rotation speed N1, and each band is determined. The

  The second reduction amount determination unit 59 determines in which of the first to fourth bands determined in this way the actual rotation speed N is accommodated, and the set amount associated with the accommodated band Is the second correction amount. The second correction amount determined in this way is used by the control selection unit 37 together with the first correction flow rate calculated by the ESS control block 31B.

  The control selection unit 37 selects a control to be executed out of the ESS control and the DSS control based on the output value of the control switching determination unit 58. More specifically, when the output value of the control switching determination unit 58 is 0, the control selection unit 37 selects the ESS control as the control to be executed, that is, selects the first correction flow rate as the correction power shift amount. On the other hand, when the output value of the control switching determination unit 58 is 1, the control selection unit 37 selects the smaller one of the first correction flow rate and the second correction flow rate as the control to be executed. The corrected power shift amount selected in this way is used in the power shift command output unit 36, and the power shift command output unit 36 outputs a power shift command that is a current command corresponding to the corrected power shift amount to the power shift valve. 20a to control the movement of the power shift valve 20a.

In the hydraulic drive system 1B configured as described above, when the differential value ΔN of the actual rotational speed N is equal to or greater than the set differential value ΔN _set and the actual rotational speed N is less than the set rotational speed N _set , ESS control is executed. . When the actual rotational speed N falls below the set rotational speed N _set while gradually decreasing, it is possible to suppress the actual rotational speed N from dropping further.

On the other hand, when the differential value ΔN becomes less than the set differential value ΔN _set , DSS control is basically executed. In the DSS control, the correction power shift amount is switched stepwise in accordance with the actual rotational speed N, and the power shift amount of the hydraulic pumps 17L and 17R is changed when the actual rotational speed N suddenly drops as in the first embodiment. It is possible to reduce the actual rotational speed N from being excessively reduced. Further, since the correction power shift amount is switched stepwise in accordance with the actual rotational speed N, when the drop in the actual rotational speed N is small, the power shift amount of the hydraulic pumps 17L and 17R is not corrected or the power shift amount is reduced. The correction is small. Therefore, it is possible to prevent the pump output of the hydraulic pumps 17L and 17R from being hindered by the correction of the power shift amount.

Further, even if the differential value ΔN is less than the set differential value ΔN _set , the actual rotation speed N is less than the first rotation speed N1, or the drop of the actual rotation speed N with respect to the set rotation speed N _set becomes large, so that the first correction is performed. When the amount becomes smaller than the second correction amount, ESS control is executed. As described above, when the actual rotational speed N is less than the first rotational speed N1 or greatly falls with respect to the set rotational speed _Nset to increase the rotational speed difference, the ESS control can be executed. This allows the actual rotational speed N is prevented from falling excessively with respect to the set rotational speed N _{The set.}

  In addition, the hydraulic drive system 1B has the same effects as the hydraulic drive system 1 of the first embodiment.

[Other Embodiments]
In the hydraulic drive systems 1, 1 </ b> A, 1 </ b> B, the correction amount of the hydraulic pumps 17 </ b> L, 17 </ b> R is calculated based on the actual rotational speed N and the differential value ΔN, and the tilt angle adjusting device 20 moves based on the calculated correction amount. However, it is not always necessary to calculate the correction amount. For example, the correction torque of the hydraulic pumps 17L and 17R and the command current input to the power shift valve 20a may be calculated, and the movement of the tilt angle adjusting device 20 may be controlled based on the calculated correction torque and command current. Further, the pump tilt angle adjusting mechanism 20 may be a mechanism in which the discharge capacity is controlled according to the command current. In the hydraulic drive systems 1, 1 </ b> A, 1 </ b> B of the present embodiment, the differential value ΔN is used as the deceleration, but a deceleration rate or a difference between the actual rotational speeds N per unit time may be used as the deceleration.

  Further, in the hydraulic drive systems 1, 1A, 1B of the present embodiment, the hydraulic actuators 11-15 are driven by the two hydraulic pumps 17L, 17R, but there may be one hydraulic pump. Further, the input means for setting the target rotational speed is not necessarily an accelerator dial, and may be an accelerator pedal or an accelerator lever.

  The construction machine on which the hydraulic pump drive systems 1, 1A, 1B are mounted is not limited to a hydraulic excavator, and may be another construction machine such as a crane or a dozer, or a construction machine provided with a hydraulic actuator. I just need it. In the hydraulic pump drive systems 1, 1 </ b> A, and 1 </ b> B, the hydraulic pump is described as an example of the hydraulic pump. However, the hydraulic pump is not limited to the hydraulic pump and may be any pump that discharges liquid such as water.

E Engine 1, 1A, 1B Hydraulic drive system 17L, 17R Hydraulic pump (hydraulic pump)
20 Tilt angle adjustment device (capacity variable mechanism)
22 Rotational speed sensor 30, 30A, 30B Control device

Claims (5)

A variable displacement hydraulic pump that is driven by an engine to discharge pressurized fluid;
A variable capacity mechanism for adjusting the pump flow rate of the hydraulic pump by controlling the discharge capacity of the hydraulic pump; and a rotational speed sensor for detecting the actual rotational speed of the engine;
A controller for controlling the movement of the variable capacity mechanism so as to control the discharge capacity of the hydraulic pump to be a predetermined target discharge capacity;
The control device calculates a deceleration of the actual rotational speed based on the actual rotational speed detected by the rotational speed sensor, and the deceleration of the actual rotational speed is a predetermined control start threshold (a non-zero negative value ). If the output is less than the target output, a reduction amount that is an output to be reduced with respect to the target output and increases in accordance with the deceleration of the actual rotational speed is calculated, and the reduction amount is reduced from the target output. A hydraulic drive system configured to control the movement of the variable capacity mechanism so that the output of the hydraulic pump is output. The movement of the engine is controlled so as to rotate at a predetermined target rotational speed,
The control device, wherein when the actual rotation speed is the higher target rotation speed is adapted to the reduction amount to zero, hydraulic drive system according to claim 1. The movement of the engine is controlled so as to rotate at a predetermined target rotational speed,
The control device, wherein when the actual rotational speed is lower than the target speed, which is the reduction amount so as to increase according to the decrease amount of the actual rotation speed, the liquid according to claim 1 or 2 Pressure drive system. The control device calculates a first reduction amount that is a correction output to be reduced with respect to the target output based on a rotational speed difference that is a difference between a preset rotational speed set in advance and the actual rotational speed, When the second reduction amount, which is a correction output that should be reduced with respect to the target output and becomes larger according to the deceleration of the actual rotational speed, is smaller than the first reduction amount, the correction is reduced from the target output. The hydraulic drive system according to any one of claims 1 to 3 , wherein a power correction output is changed from a second reduction amount to the first reduction amount. The control start threshold value, the is set as a dead zone, also the actual rotation speed is reduced and the control device does not pump output of the hydraulic pump lower than the target output occurs, one of claims 1 to 4 The hydraulic drive system as described in any one.

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