CN105889015B - Fluid power system - Google Patents

Abstract

The present invention provides a hydraulic drive system that suppresses the excessive drop of the rotational speed of the engine and has high reliability when the engine load increases. The hydraulic drive system (1) includes: an engine (E); variable capacity hydraulic pumps (17L, 17R); a tilt angle adjustment device (20); a rotational speed sensor (22); and a control device (30). The control device (30) controls the operation of the tilt angle adjusting device (20) to change the discharge capacity of the hydraulic pump (17L, 17R) so that the pump torque of the hydraulic pump (17L, 17R) reaches the target command torque. In addition, when the control device (30) raises the pump torque to the target command torque, if the real-time rotational speed of the engine E detected by the rotational speed sensor 22 is lower than the control start rotational speed, the pump torque is varied by a preset upper limit The rate of change below the rate increases from the standby torque which is smaller than the target command torque to the target command torque.

Description

hydraulic drive system

technical field

The present invention relates to a hydraulic drive system capable of controlling the discharge capacity of a variable capacity hydraulic pump that is driven by an engine and discharges pressure fluid.

Background technique

Construction machines and the like are equipped with hydraulic pumps that are rotationally driven by engines, and pressurized oil is discharged from the hydraulic pumps when operating elements such as operating levers are manipulated. The discharged pressure oil is introduced into hydraulic actuators such as hydraulic cylinders to operate the hydraulic actuators. Since the hydraulic actuator works, the stick (arm) or the boom (boom) etc. executes the movement. When the hydraulic actuator is operated by the pressurized oil from the hydraulic pump, the load applied to the engine increases and the rotational speed of the engine decreases. As a device for suppressing the above-mentioned decrease in engine rotation speed, devices of Patent Document 1 and Patent Document 2 are known, for example.

In the discharge amount control device of Patent Document 1, a set reference rotation speed is set, and when the actual rotation speed of the engine is lower than the set reference rotation speed, the rotation speed deviation between the set reference rotation speed and the actual engine rotation speed is reduced. The pump absorbs torque (ie, discharge flow), thereby reducing the load on the engine.

Also, the engine control device of Patent Document 2 has a control valve that controls the flow rate of hydraulic oil flowing into the hydraulic actuator, and pilot oil from a remote control valve is input to the control valve through a pilot oil passage. A pressure switch is provided in the pilot oil circuit, and the operation of the hydraulic actuator is detected through the pressure switch. When the operation of the hydraulic actuator is detected, the torque of the main pump is increased from the low torque to the specified high torque.

Prior art literature:

Patent documents:

Patent Document 1: Japanese Patent Publication No. 6-58111;

Patent Document 2: Specification of Japanese Patent No. 3688969.

Contents of the invention

Problems to be solved by the invention:

In the discharge amount control device of Patent Document 1, the pump absorption torque (i.e., the discharge flow rate) is reduced in accordance with the rotational speed deviation between the set reference rotational speed and the actual rotational speed of the engine, so it is necessary to set the set reference rotational speed relatively low. Low. At this time, the pump absorption torque is reduced after the speed at which the actual rotational speed drops increases, so the actual rotational speed drops greatly. In order to solve such a problem, in the engine control device of Patent Document 2, the torque of the main pump is raised from a low torque to a predetermined high torque at the same time as the operation of the hydraulic actuator is started.

However, in the engine control device of Patent Document 2, the start of operation of the hydraulic actuator is detected by the pressure switch. Therefore, the number of parts increases, and the cost of the system structure increases. Also, since the pressure switch has a contact structure, the number of operations is limited, and the reliability is lowered.

Therefore, an object of the present invention is to provide a highly reliable hydraulic drive system that suppresses an excessive drop in engine speed when the engine load increases.

Means to solve the problem:

The hydraulic drive system of the present invention includes: an engine controlled by a rotational speed control device in the form of rotational drive at a preset set rotational speed; a variable capacity hydraulic pump that is rotationally driven by the engine and discharges pressure fluid; a variable displacement mechanism for adjusting the pump torque of the hydraulic pump by adjusting the discharge capacity of the hydraulic pump; a load sensor for detecting the load of the engine; and controlling the operation of the variable displacement mechanism so that the A control device for changing the discharge capacity of the hydraulic pump in such a manner that the pump torque of the hydraulic pump reaches a preset target command torque; the control device determines whether the load of the engine is based on the detection result detected by the load sensor The pump torque of the hydraulic pump is changed at a preset upper limit by controlling the operation of the variable displacement mechanism when the load of the engine reaches a preset control start threshold or more. The rate of change below the rate increases from the standby torque smaller than the target command torque to the target command torque.

According to the present invention, since the pump torque of the hydraulic pump can be gradually increased, it is possible to prevent a sudden increase in the load on the engine that operates the hydraulic pump. With this, it is possible to suppress an excessive drop in the real-time rotational speed of the engine. In addition, the control device controls the operation of the variable displacement mechanism based on the load of the engine, thereby reducing the number of operations of pressure sensors with mechanically movable mechanisms, such as pressure switches, and improving the reliability of the hydraulic drive system.

It may also be in the above invention that the hydraulic pump changes the discharge capacity by adjusting its inclination angle; the variable capacity mechanism has a servo mechanism for switching the inclination angle of the hydraulic pump, and shifts gears based on inputted power command to adjust the control valve of the servo mechanism; the control device has a target current calculation unit, a standby current calculation unit, a current command value selection unit, a control execution determination unit, and a change rate limitation unit; The pump torque of the hydraulic pump reaches the target command torque, and a target current is calculated as a current command value to be input to the control valve; torque reaches the standby torque, and calculates the standby current as the current command value to be input to the control valve; the current command value selection unit determines the load of the engine in the control execution determination unit When the value is less than the control start threshold, the standby current calculated by the standby current calculation unit is selected as the current command value, and when the control execution determination unit determines that the load on the engine is equal to or greater than the control start threshold, selecting the target current calculated by the target current calculation unit as the current command value; the rate-of-change limiting unit calculating a power shift command value that limits the rate of change of the current command value to be equal to or less than the upper limit rate of change , and output the power shift command corresponding to the power shift command value to the control valve.

According to the above configuration, when the engine load is lower than the control start threshold, a power shift command corresponding to the standby current is output to the control valve, and the pump torque of the hydraulic pump can be made to be the standby torque. Also, when the load on the engine is equal to or greater than the control start threshold value, the current command value is switched from the standby current to the target current so that the pump torque of the hydraulic pump reaches the target command torque. When the current command value is switched to increase from the standby current to the target current, the rate of change of the power shift command value is limited to the upper limit rate of change by the change rate limiting unit, so that the power shift command value can be gradually increased. With this, the pump torque of the hydraulic pump can be gradually increased, and as a result, the load on the engine driving the hydraulic pump can be prevented from suddenly increasing.

In the above invention, when the pump torque of the hydraulic pump is increased from the standby torque to the target command torque, the control device may change The upper limit rate of change.

According to the above structure, the upper limit change rate of the change rate of the pump torque can be changed according to the characteristics of the engine or the hydraulic pump, or the like. For example, the upper limit change rate can be reduced in a low torque state where the response speed of the engine is slow, and the upper limit change rate can be increased as the pump torque increases. With this, it is possible to suppress an excessive decrease in the real-time rotation speed of the engine, and to shorten the time required for the pump torque to reach the target command torque.

In the above invention, the control device may set a torque upper limit value corresponding to the detection result detected by the load sensor, and set a value between the standby torque and the target command torque. When changing the pump torque of the hydraulic pump, the pump torque of the hydraulic pump is limited to be equal to or less than the torque upper limit value.

According to the above configuration, the torque upper limit value can be set according to the engine load, for example, the torque upper limit value can be lowered as the engine load decreases. With this, the pump torque can be reduced as the engine load decreases, and the torque upper limit value changes with the engine load, so even if the engine load suddenly increases in the middle of the engine load decrease, the Since the pump torque is limited to be equal to or less than the torque upper limit, it is possible to gradually increase the pump torque from a relatively low torque to the target command torque. With this, even if the engine load increases again while the engine load is decreasing, it is possible to suppress an excessive drop in the real-time rotation speed of the engine.

Preferably, in the above invention, the load sensor includes a rotation speed sensor for detecting a real-time rotation speed of the engine; and the control execution determination section determines the load of the engine based on the real-time rotation speed detected by the rotation speed sensor. Whether it reaches above the control start threshold.

The variation of the load of the engine can be indirectly detected by the rotation speed sensor according to the variation of the real-time rotation speed of the engine. According to the above configuration, the pump torque can be controlled based on the detected real-time rotation speed, and the pump torque can be controlled by the rotation speed sensor attached to the engine.

In the above invention, the control device may be configured as follows: when the real-time rotational speed detected by the rotational speed sensor is lower than a reference rotational speed, based on the rotational speed between the real-time rotational speed and the set rotational speed, The difference reduces the pump torque of the hydraulic pump, and the reference rotational speed is smaller than the control start rotational speed corresponding to the control start threshold.

According to the above-mentioned configuration, when the real-time engine speed is significantly lower than the control start threshold value and becomes smaller than the reference speed, the pump torque can be reduced based on the difference in speed. The pump torque is reduced based on the rotational speed difference while limiting the upper limit change rate of the pump torque, thereby preventing an excessive drop in the real-time rotational speed of the engine.

Preferably, in the above invention, the load sensor includes a pump pressure sensor that detects a pump pressure that is the discharge pressure of the hydraulic pump; and the control execution determination unit is based on the pump pressure detected by the pump pressure sensor. It is determined whether or not the engine load is equal to or greater than the control start threshold.

The change in the load of the engine can be detected indirectly from the change in the pump pressure of the hydraulic pump by the pump pressure sensor. According to the above configuration, the pump torque can be controlled based on the detected pump pressure, and the pump torque can be controlled based on the pump pressure that quickly reflects the load fluctuation of the engine. With this, the responsiveness to engine load fluctuations can be improved, a sudden increase in engine load can be further suppressed, and excessive fuel injection during transition can be suppressed.

Preferably, in the above invention, the load sensor includes a speed sensor for detecting the real-time speed of the engine; the control device, when the real-time speed detected by the speed sensor is lower than the reference speed, The pump torque of the hydraulic pump is reduced by the difference in rotation speed between the real-time rotation speed and the set rotation speed, the reference rotation speed being set as the engine load in a state where the load of the engine is greater than the control start threshold value. Rotating speed.

According to the above-mentioned configuration, when the real-time engine speed is significantly lower than the control start threshold value and becomes smaller than the reference speed, the pump torque can be reduced based on the difference in speed. The pump torque is reduced based on the rotational speed difference while limiting the upper limit change rate of the pump torque, thereby preventing an excessive drop in the real-time rotational speed of the engine.

Invention effect:

According to the present invention, it is possible to suppress an excessive drop in the rotational speed of the engine when the engine load increases, and to improve reliability.

Description of drawings

1 is a block diagram showing a hydraulic drive system according to the first embodiment to the fourth embodiment of the present invention;

2 is a schematic circuit diagram showing the structure of a tilt angle adjusting device of a hydraulic drive system;

Fig. 3 is a functional block diagram showing the functions of the control device equipped in the hydraulic drive system of the first embodiment and the second embodiment in blocks;

Fig. 4 is a flow chart showing steps when the control device of Fig. 3 boosts the torque of the hydraulic pump;

Fig. 5 is a graph showing changes with time of various values when the hydraulic drive system of the first embodiment is operated;

6 is a graph showing the relationship between various values and the engine speed when the hydraulic drive system of the first embodiment is operated;

7 is a flow chart showing steps when the control device according to the second embodiment increases the torque of the hydraulic pump;

Fig. 8 is a graph showing changes with time of various values when the hydraulic drive system of the second embodiment is operated;

Fig. 9 is a functional block diagram showing the functions of the control device equipped in the hydraulic drive system of the third embodiment in blocks;

Fig. 10 is a flow chart showing steps when the control device according to the third embodiment increases the torque of the hydraulic pump;

11 is a graph showing the relationship between various values and the engine speed when the hydraulic drive system of the third embodiment is operated;

Fig. 12 is a functional block diagram showing the functions of the control device equipped in the hydraulic drive system of the fourth embodiment in blocks;

Fig. 13 is a flow chart showing steps when the control device according to the fourth embodiment increases the torque of the hydraulic pump;

14 is a graph showing the relationship between pump torque and pump pressure in the hydraulic drive system of the fourth embodiment;

15 is a graph showing the relationship between pump torque and engine speed in the hydraulic drive system of the fourth embodiment;

Symbol Description:

E engine;

1. 1A, 1B hydraulic drive system;

17L, 17R hydraulic pump (hydraulic pump);

20 Tilt angle adjustment device (variable capacity mechanism);

21 Engine speed control equipment;

22 speed sensor;

30, 30A, 30B, 30C control gear;

31 target current calculation unit;

32 Standby current setting part (standby current calculation part);

33. 33C control execution judgment part;

34 current command value selection unit;

38, 38A, 38B rate-of-change limiting section;

39, 39C upper limit limit department;

51 the first pump pressure sensor;

52 Second pump pressure sensor.

detailed description

Hereinafter, hydraulic drive systems 1 , 1A, 1B, and 1C according to the first embodiment to the fourth embodiment 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 of description, and is not intended to limit the direction etc. of the structure of this invention to this direction. In addition, the hydraulic drive systems 1, 1A, and 1B described below are merely one embodiment of the present invention. Therefore, the present invention is not limited to the embodiments, and additions, deletions, and changes are possible within a range not departing from the gist of the invention.

[First Embodiment]

Construction machinery has various accessories such as buckets, loaders, scrapers, and hoists, and can be driven by hydraulic actuators such as hydraulic cylinders or hydraulic motors. For example, a hydraulic excavator, which is one type of construction machinery, includes a bucket, an arm, and a boom, and can perform operations such as excavation while operating these three components. The bucket, the arm, and the boom are respectively provided with hydraulic cylinders 11 to 13 , and the bucket, the arm, and the boom are operated by supplying pressurized oil to the respective cylinders 11 to 13 .

Moreover, the hydraulic excavator has a traveling device, and a revolving body is rotatably attached to the traveling device. A boom is attached to the rotary body so as to be swingable in the up and down direction. A hydraulic rotation motor 14 is attached to the rotating body, and the rotating body is rotated by supplying pressure oil to the rotating motor 14 . Also, hydraulic travel motors 15 (left travel motor 15L and right travel motor 15R) are attached to the travel device, and the travel motor 15 is supplied with pressure oil to move forward or backward.

In addition, in the hydraulic excavator, the following operation valves 19 are provided corresponding to the hydraulic actuators 11 to 15, respectively. In addition, only one operating valve 19 is shown in FIG. 1 . The hydraulic actuators 11-15 (that is, hydraulic cylinders 11-13 and hydraulic motors 14, 15) are connected to the hydraulic supply device 16, and when any one of the operating parts of the plurality of operating valves 19 is operated, oil The pressure supply device 16 supplies pressure oil to the hydraulic actuators 11 to 15 corresponding to the operation valve 19 to operate the corresponding hydraulic actuators 11 to 15 .

As described in more detail, the hydraulic supply device 16 has two hydraulic pumps 17L, 17R, a hydraulic control valve 18 , a plurality of operation valves 19 , and two tilt angle adjustment devices 20 . The two hydraulic pumps 17L and 17R share one rotating shaft 17a, and the pressure oil is discharged by rotating the rotating shaft 17a. Pressurized oil discharged from hydraulic pumps 17L and 17R is introduced into hydraulic control valve 18 . The hydraulic control valve 18 is connected to a plurality of operation valves 19 . The operating valve 19 has an unillustrated operating member (operating rod, etc.), and when any one of the operating rods of the plurality of operating valves 19 is operated, pressure oil flows into the hydraulic actuator corresponding to the operated operating member. 11 to 15 forms control the flow of pressure oil.

Each operation valve 19 outputs pilot oil at a pressure corresponding to the operation amount of the operation element (for example, pouring amount) in a direction corresponding to the operation direction of the operation element (for example, pouring direction) when the operation element is operated. The output pilot oil is introduced into the hydraulic control valve 18, and the hydraulic control valve 18 controls the flow of the pressure oil discharged from the hydraulic pumps 17L, 17R according to the output pilot oil. That is, the oil pressure control valve 18 flows pressurized oil into the oil pressure actuators 11 to 15 corresponding to the operated operating elements to operate them. In addition, the hydraulic control valve 18 supplies pressure oil at a flow rate corresponding to the pilot pressure output from the operating member to the corresponding hydraulic actuators 11 to 15, so that the hydraulic actuators 11 to 15 are controlled at the same rate as the operating amount of the operating member. corresponding speed work. In this way, the bucket, the arm, the boom, and the like can be operated at a speed corresponding to the amount of operation of the operating element.

In the hydraulic supply device 16 having such a structure, variable displacement type pumps can be used as the hydraulic pumps 17L, 17R, and variable displacement type swash plate pumps are used in this embodiment. In addition, since the hydraulic pumps 17L and 17R have the same structure, only the structure of one hydraulic pump 17L will be described, and the description of the structure 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 17L is provided with a tilt angle adjusting device 20 to change the tilt angle of the swash plate 17b. The tilt angle adjusting device 20 has a power shift valve 20a and a servo mechanism 20b. The power shift valve 20a is, for example, an electromagnetic proportional valve, and is connected to an unillustrated pilot pump. The power shift valve 20 a outputs a power shift pressure p ₁ corresponding to a power shift command (tilt angle command) output from a control device 30 described later. The power shift valve 20a is connected to the servomechanism 20b, and the output drive oil is introduced into the servomechanism 20b.

The servo mechanism 20b has an unillustrated servo piston. The servo piston is connected to the swash plate 17b, and the inclination angle of the swash plate 17b can be changed by moving the servo piston. _The servo piston moves with the power shift pressure p1. That is, the inclination angle of the swash plate 17b is adjusted to _an angle corresponding to the power shift pressure p1. In this embodiment, the servo mechanism 20b decreases the inclination angle _of the swash plate 17b when the power shift pressure p1 increases, and increases the inclination angle _of the swash plate 17b when the power shift pressure p1 decreases. In this way, the tilt angle adjusting device 20 adjusts the tilt angle to change the discharge capacity of the hydraulic pump 17L, thereby adjusting the pump torque of the hydraulic pump 17L.

In the present embodiment, the hydraulic supply device 16 is configured as a negative control type hydraulic system, and outputs a negative control pressure to the tilt angle adjusting device 20 . In addition, the hydraulic supply device 16 may be constituted by a positive control type hydraulic system. The servo mechanism 20b adjusts the inclination angle of the swash plate 17b to an angle corresponding to the smaller _one of the inclination angle determined by the negative control pressure and the inclination angle determined by the power shift pressure p1. In such a configuration, the maximum discharge capacity (that is, the maximum pump torque) of the hydraulic pumps 17L, 17R can be limited by the power shift pressure p1. The engine E is provided on the rotary shafts 17a of the hydraulic pumps 17L and 17R configured in this way.

The engine E rotationally drives the rotary shafts 17a of the hydraulic pumps 17L, 17R. In this embodiment, a diesel engine can be used as the engine E, and the engine E has the engine rotation speed control device 21 . The engine rotational speed control device 21 is a so-called mechanical governor, and has a governor motor for adjusting a speed adjustment lever. The engine rotation speed control device 21 controls the rotation speed of the engine E by changing the position of the speed adjustment lever through the governor motor. In the engine rotation speed control device 21, a set rotation speed command value for adjusting the position of the speed adjustment lever is input to the governor motor. Also, the engine rotational speed control device 21 adjusts the fuel injection amount of the engine E in such a manner that the rotational speed of the rotary shaft 17a is adjusted to a set rotational speed command value. In addition, the engine E does not necessarily have to be a mechanical governor engine, and may be an electronic governor engine. In the case of an electronic governor engine, the ECU can be used as the engine rotation speed control device 21, and the fuel injection amount of the fuel injection device is electronically controlled by the ECU, thereby adjusting the rotation speed of the rotary shaft 17a to the set rotation speed command value.

Also, a rotational speed sensor 22 is attached to the rotational shaft 17a. The rotational speed sensor 22 is a load sensor for detecting the load of the engine E and outputs a signal corresponding to the rotational speed of the rotational shaft 17a. The rotational speed sensor 22 is electrically connected to the control device 30 . The control device 30 calculates the actual rotational speed of the engine E, that is, the real rotational speed based on the signal from the rotational speed sensor 22 . In addition, the control device 30 is electrically connected to an accelerator dial 24 and a power mode input device 25 .

The accelerator dial 24 is a disk-type rotational speed setting device for setting the rank of the set rotational speed, that is, an accelerator rank, and the power mode input device 25 is an operation instruction device for inputting a power mode. The accelerator dial 24 and the power mode input device 25 output a signal corresponding to an instruction value set by the driver to the control device 30 .

The control device 30 has a set rotation speed calculation map in which the set rotation speed corresponds to signals output from the accelerator dial 24 and the power mode input device 25 . Here, the set rotation speed is the rotation speed of the engine E set as a target during standby (idling). The control device 30 calculates the set rotation speed based on the two signals respectively output from the accelerator dial 24 and the power mode input device 25 using the set rotation speed calculation map. Furthermore, the control device 30 outputs a set rotation speed command corresponding to the calculated set rotation speed to the engine rotation speed control device 21, and controls the fuel consumption of the engine E through the engine speed control device 21 so that the rotation speed of the engine E reaches the set rotation speed. Injection volume.

The control device 30 configured in this way outputs a power shift command to the power shift valve 20 a of the tilt angle adjusting device 20 to adjust the pump torque of the swash plate 17 b of the hydraulic pumps 17L, 17R. The control device 30 has a functional part for calculating various values shown in FIG. 3 in order to output a power shift command, and various values are calculated at predetermined intervals. Hereinafter, each functional portion that calculates various values is divided into modules and described.

The control device 30 has a target current calculation unit 31 , a standby current setting unit 32 , a control execution determination unit 33 , a current command value selection unit 34 , an engine speed sensing control unit (abbreviation: ESS control unit) 36 , and a current command subtraction unit. 37 and rate of change limiting unit 38. The target current calculation unit 31 calculates a target current which is a current command value to be output to the power shift valve 20a in order to achieve the target command torque of the pump torque of the hydraulic pumps 17L, 17R. The target command torque is a pump torque set based on the real-time rotation speed detected by the rotation speed sensor 22 and the power mode. In addition, the pump torque does not necessarily have to be set according to the real-time rotation speed and power mode, but can also be set according to the accelerator level and power mode.

In the present embodiment, the direct target current is calculated from the real-time rotational speed and the power mode as follows. That is, the target current calculation unit 31 has a target current calculation map. In the target current calculation map, the target current corresponds to the real-time speed and power mode. The target current calculation unit 31 calculates the real-time rotational speed based on the signal output from the rotational speed sensor 22 . Furthermore, target current calculation unit 31 determines a power mode based on a signal output from power mode input device 25 . Furthermore, the target current calculation unit 31 can calculate the target current based on the real-time rotational speed and the power mode by using the target current calculation map. In this way, the target current calculation unit 31 calculates a target current corresponding to the target command torque.

Also, the standby current setting unit 32 sets the standby current. The standby current is a current command value to be output to the power shift valve 20a so that the pump torque of the hydraulic pumps 17L, 17R becomes the standby torque. The standby torque is the pump torque of the hydraulic pumps 17L, 17R when the tilt angle of the hydraulic pumps 17L, 17R is set to a small tilt angle, and is a preset torque of the hydraulic pumps 17L, 17R, for example is the necessary minimum torque.

The control execution determination section 33 sets the control start rotation speed r1, and determines whether or not the real-time rotation speed of the engine E as a detection result is smaller than the control start rotation speed r1. As described in more detail, the control execution determination unit 33 has a control start rotation speed calculation map corresponding to the control start rotation speed r1 and the set rotation speed. The control execution determination unit 33 calculates and sets the control start rotation speed r1 based on the set rotation speed using the control start rotation speed calculation map. Furthermore, the control execution determination unit 33 calculates the real-time rotational speed of the engine E based on the signal from the rotational speed sensor 22, and determines whether the real-time rotational speed is smaller than the control start rotational speed r1. The real-time rotational speed of the engine E as a determination object decreases when the load on the engine E increases, and increases when the load on the engine E decreases. The control execution determination unit 33 determines whether the real-time rotation speed of the engine E is lower than the control start rotation speed r1, thereby determining whether the load on the engine E is equal to or greater than a preset control start threshold. That is, the control execution determination unit 33 determines based on the real-time rotation speed of the engine E whether or not the load on the engine E is equal to or greater than a control start threshold value corresponding to the control start rotation speed r1.

Further, the control execution determination unit 33 sets the control end rotation speed r3, and determines whether the real time rotation speed of the engine E is smaller than the control end rotation speed r3. As described in more detail, the control execution determination unit 33 has a control-completed rotational speed calculation map in which the controlled-completed rotational speed r3 corresponds to the set rotational speed. The control execution determination unit 33 calculates and sets the control-end rotation speed r3 based on the set rotation speed using the control-end rotation speed calculation map. After setting, the control execution determination unit 33 determines whether or not the real-time rotation speed is smaller than the control end rotation speed r3. The above-mentioned relationship exists between the real-time rotation speed of the engine E and the load, so the control execution determination unit 33 determines whether the real-time rotation speed of the engine E is lower than the control-end rotation speed r3 to determine whether the load of the engine E is equal to or greater than the control-end threshold. That is, the control execution determination unit 33 determines based on the real-time rotation speed of the engine E whether or not the load on the engine E is equal to or greater than a control termination threshold value corresponding to the control termination rotation speed r3.

In addition, in the present embodiment, the maps for calculating the control start rotation speed r1 and the control end rotation speed r3 are respectively used, and the same map is used, and the control start rotation speed r1 and the control end rotation speed r3 are set to the same value. However, each map may be different, and the control start rotation speed r1 and the control end rotation speed r3 may have hysteresis (control start rotation speed r1<control end rotation speed r3 ) according to the different maps. The determination result in the control execution determination unit 33 is used in the current command value selection unit 34 together with the target current and the standby current.

The current command value selection unit 34 selects either one of the target current and the standby current as the first current command value based on the determination result of the control execution determination unit 33 . Specifically, the current command value selection unit 34 selects the standby current as the first current command value when the control execution determination unit 33 determines that the real-time rotation speed is greater than or equal to the control start rotation speed r1 or the control end rotation speed r3 . On the other hand, when the control execution determination unit 33 determines that the real-time rotation speed is lower than the control start rotation speed r1 or the control end rotation speed r3 , the current command value selection unit 34 selects the target current as the first current command value. Also, the ESS control unit 36 executes calculation processing in parallel with the setting of the first current command value.

The ESS control unit 36 further restricts the pump torques of the hydraulic pumps 17L, 17R in order to suppress a further drop in the real-time rotational speed of the engine E when the reference rotational speed r2 which is lower than the control start rotational speed r1 is reached. That is, the ESS control unit 36 calculates a reduction current command value for reducing the pump torque of the hydraulic pumps 17L, 17R based on the rotational speed difference of the difference between the real rotational speed and the reference rotational speed r2. As described in more detail, the ESS control unit 36 determines whether or not the real-time rotation speed is equal to or less than the reference rotation speed r2. When the real-time rotation speed is equal to or greater than the reference rotation speed r2, the ESS control unit 36 sets the reduction current command value to zero. On the other hand, when the real-time rotation speed is lower than the reference rotation speed r2, the ESS control unit 36 calculates a rotation speed difference, and calculates a reduction current command value using a control calculation formula of PID control based on the calculated rotation speed difference. In addition, the control calculation formula used is not limited to the control calculation formula of PID control, The control calculation formula of PI control may be sufficient. The calculated reduced current command value is used in the current command subtraction unit 37 together with the set first current command value.

The current command subtraction unit 37 subtracts the reduced current command value calculated by the ESS control unit 36 from the first current command value set by the current command value selection unit 34 . Therefore, when the real-time rotation speed is equal to or greater than the reference rotation speed r2 (that is, when ESS control is not performed), the reduced current command value is zero, and the second current command value, which is a value obtained by subtraction, becomes the first current command value. On the other hand, when the real-time rotation speed is lower than the reference rotation speed r2 (that is, when ESS control is being performed), a value obtained by subtracting the reduced current command value from the first current command value is calculated as the second current command value. The calculated second current command value is used in the rate-of-change limiting unit 38 .

The change rate limiting unit 38 limits the change rate of the power shift command value calculated based on the second current command value so as to prevent it from exceeding a preset upper limit change rate. As described in more detail, the rate-of-change limiting unit 38 holds the power shift command value just calculated, and divides the second current command value calculated by the current command subtraction unit 37 by the held power shift command value to calculate the relative power shift command value. The rate of change of the power shift command value. When the calculated rate of change is equal to or greater than the upper limit rate of change, rate-of-change limiting unit 38 multiplies the held power shift command value by the upper limit rate of change of the rate of change to calculate and hold a new power shift command value. On the other hand, when the calculated rate of change is smaller than the upper limit rate of change, rate-of-change limiting unit 38 calculates and holds the second current command value as a new power shift command value as it is. In this way, the change rate limiting unit 38 limits the power shift command value (that is, the pump torque of the hydraulic pumps 17L, 17R) so as not to exceed the upper limit change rate.

Furthermore, the rate-of-change limiting unit 38 outputs a power shift command corresponding to the calculated power shift command value to the power shift valve 20a. The power shift valve 20a outputs a power shift pressure p ₁ corresponding to a power shift command (tilt angle command). When the output power shift pressure p1 is greater _than the oil pressure of the pilot oil from the operating member, the inclination angle of the swash plate 17b of the servo mechanism 20b is adjusted to _an angle corresponding to the power shift pressure p1.

In this way, the change rate limiting unit 38 limits the power shift command value so that the change rate of the power shift command value does not exceed the upper limit change rate. The rate of change limiting unit 38 limits the rate of change of the power shift command value below the upper limit rate of change when the first current command value is switched from the standby current to the target current, and increases the power shift command value to the target current. In this way, the control device 30 controls the operation of the tilt angle adjusting device 20 to change the discharge capacity of the hydraulic pumps 17L, 17R, and the pump torque of the hydraulic pumps 17L, 17R can be changed from the standby mode at a rate of change equal to or less than the upper limit rate of change. torque up to the target command torque.

The hydraulic drive system 1 having such a structure adjusts the inclination angle of the swash plate 17b to suppress the pump torque of the hydraulic pumps 17L, 17R when the load on the hydraulic pumps 17L, 17R increases and the rotational speed of the engine E decreases. Hereinafter, the engine load suppression control processing (ie, engine load control processing) of the control device 30 will be described with reference to FIGS. In addition, FIG. 5 shows a graph sequentially showing the rotational speed of the engine E, the pump torques of the hydraulic pumps 17L and 17R, and the power shift command value over time from the top, the vertical axis represents various values, and the horizontal axis The axis represents time. In addition, FIG. 6 shows a graph sequentially showing changes in the output torque of the engine E and the power shift command value with respect to the rotation speed of the engine E from above. The vertical axis represents various values, and the horizontal axis represents the engine speed. In the hydraulic drive system 1, when the engine E is driven, the control device 30 starts the engine load suppression process, and proceeds to step S1.

In the standby current output process as step S1, the standby current set by the standby current setting unit 32 is selected as the first current command value. The first current command value as the standby current is calculated as the power shift command value without being restricted by the rate-of-change limiting unit 38 . Also, with this, a power shift command corresponding to the standby current is output from the control device 30 to the power shift valve 20a, and the inclination angle of the swash plate 17b of the hydraulic pumps 17L, 17R becomes small. Then, the pump torque of the hydraulic pumps 17L, 17R becomes the standby torque, and the load acting on the engine E from the hydraulic pumps 17L, 17R can be made to a necessary minimum limit. In this way, when the load on the engine E reaches the necessary minimum, step S1 ends, and the process proceeds to step S2.

In the first engine rotation speed determination step as step S2, the control execution determination unit 33 determines whether or not the real-time rotation speed of the engine E is lower than the control start rotation speed r1. As described in detail, the control execution determination unit 33 uses the control start rotation speed calculation map to set the control start rotation speed based on the accelerator level (more specifically, the engine speed at standby determined by the accelerator dial and the power mode) and the power mode. r1, and determine whether the real-time rotational speed of the engine E is lower than the control start rotational speed r1. When the control execution determination unit 33 determines that the real-time rotation speed has reached the control start rotation speed r1 or more (that is, the load on the engine E is smaller than the control start threshold value) (refer to time t0 to time t1 in FIG. The corresponding power shift command is continuously output from the control device 30 to the power shift valve 20a. That is, the pump torque of the hydraulic pumps 17L, 17R is maintained at the standby torque until the real rotation speed is lower than the control start rotation speed r1 (that is, until the load on the engine E becomes equal to or greater than the control start threshold). On the other hand, when the control execution determination unit 33 determines that the real-time rotation speed is lower than the control start rotation speed r1 (see time t1 to time t3 in FIG. 5 ), the process proceeds to step S3.

In the current switching process as step S3, based on the determination result of the control execution determination unit 33, the current command value selection unit 34 selects the target current as the first current command value, and switches the first current command value from the standby current to the target current. . When the first current command value is switched from the standby current to the target current, the process proceeds to step S4.

In the rate of change limiting process as step S4, the rate of change of the power shift command value is limited by the rate of change limiting unit 38 so as to prevent it from exceeding the upper limit rate of change. That is, the rate-of-change limiting unit 38 calculates the power shift command value based on the second current command value. In addition, when the real-time rotation speed is equal to or higher than the reference rotation speed r2, the low current command value is zero, so the second current command value is equal to the first current command value. As a result, the change rate limiting unit 38 calculates a power shift command value based on the first current command value. By calculating the power shift command value in this way, the rate of change of the power shift command value is limited, and the power shift command value is gradually increased (see times t1 to t2 in FIG. 5 ). As a result, the pump torques of the hydraulic pumps 17L and 17R can be ramped up gradually, thereby suppressing an excessive drop in the real-time rotational speed due to a sudden increase in the load on the engine E. In addition, in the hydraulic drive system 1, the determination of the start of control is performed based on the real-time rotational speed. Therefore, in the hydraulic drive system 1 , it is possible to reduce the number of operations of the pressure sensor having a mechanically movable mechanism, such as a pressure switch, which has a limited number of operations, thereby improving the reliability of the hydraulic drive system 1 . In addition, by omitting the pressure sensor, the number of parts can be reduced, and the manufacturing cost of the hydraulic drive system 1 can be reduced. In this way, the power shift command value is increased while limiting the rate of change of the power shift command value, and the process proceeds to step S5.

In the ESS control process as step S5, the ESS control unit 36 executes the ESS control when the real-time rotation speed is lower than the reference rotation speed r2. ESS control is engine speed sensing control, and is a control to reduce the pump torque of hydraulic pumps 17L, 17R by PID control based on the difference between the actual rotation speed and the set rotation speed when the actual rotation speed is lower than the reference rotation speed r2.

In the present embodiment, when the ESS control unit 36 determines that the real-time rotational speed is lower than the reference rotational speed r2 , it calculates the reduction current command value based on the rotational speed difference that is the difference between the real-time rotational speed and the set rotational speed. The current command subtraction unit 37 subtracts the reduced current command value from the first current command value set by the current command value selection unit 34 to calculate a second current command value. The change rate limiting unit 38 calculates a power shift command value based on the calculated second current command value, and outputs a power shift command corresponding to the power shift command value to the power shift valve 20a. By executing such ESS control, when the real-time rotational speed falls below the reference rotational speed r2, the pump torques of the hydraulic pumps 17L, 17R can be gradually reduced according to the drop of the real-time rotational speed (in the graph of the power shift command value in FIG. 6 , refer to the left of the reference speed r2). With this, when the real-time rotation speed of the engine E drops even though the rate of change of the power shift command value is suppressed, further drops can be prevented. After execution of the ESS control, when the ESS control unit 36 determines that the real-time rotation speed is equal to or greater than the reference rotation speed r2, the ESS control ends and the process proceeds to step S6.

On the other hand, when the ESS control unit 36 determines that the real-time rotation speed is equal to or greater than the reference rotation speed r2, the ESS control unit 36 sets the current reduction command value to zero and does not execute the ESS control. In addition, in the graph shown in FIG. 5 , the ESS control is not executed, and the pump torque of the hydraulic pumps 17L, 17R can be quickly raised to a desired torque. Even when the ESS control is not executed in this way, the process proceeds to step S6.

In the target current attainment determination process as step S6 , the rate-of-change limiting unit 38 determines whether or not the power shift command value has reached the target current. That is, the control device 30 determines whether the pump torque of the hydraulic pumps 17L, 17R has reached the target command torque. When the rate-of-change limiting unit 38 determines that the power shift command value has not reached the target current (that is, the pump torque has not reached the target command torque), it returns to step S4 and the control device 30 increases the power shift command value. On the other hand, when the rate-of-change limiting unit 38 determines that the power shift command value has reached the target current (that is, the pump torque has reached the target command torque), the process proceeds to step S7.

In the second engine rotation speed determination process as step S7, the control execution determination unit 33 determines whether or not the real-time rotation speed of the engine E is lower than the control end rotation speed r3. When the control execution determination unit 33 determines that the real-time rotational speed is lower than the control termination rotational speed r3 (that is, the load on the engine E is equal to or greater than the control termination threshold value) (see time t2 to time t3 in FIG. 5 ), the current command value selection unit 34 continues to select the target The current is used as the first current command value, and the process returns to step S5. On the other hand, when the control execution determination unit 33 determines that the real-time rotation speed has reached the control end rotation speed r3 or more (that is, the load on the engine E is less than the control end threshold value), return to step S1, and the first current command The value switches from target current to standby current. As a result, the power shift command value is reduced to the standby current, and the pump torques of the hydraulic pumps 17L, 17R are reduced to the necessary minimum (see time t3 in FIG. 5 ).

The hydraulic drive system 1 having such a configuration can suppress an excessive drop in the real-time rotational speed due to a sudden increase in the load on the engine E as described above, and as a result, excessive fuel injection at the time of transition can be suppressed. Also, the reliability of the hydraulic drive system 1 can be improved.

In addition, in the hydraulic drive system 1 , it is possible to indirectly detect a change in the load of the engine E through a change in the real-time rotational speed of the engine E, and it is possible to control the pump torque based on the detected real-time rotational speed. Therefore, the pump torque can be controlled by the rotational speed sensor 22 attached to the engine E. As shown in FIG.

[Second Embodiment]

A hydraulic drive system 1A of the second embodiment is similar in structure to the hydraulic drive system 1 of the first embodiment. Hereinafter, with regard to the hydraulic pump drive system 1A, only the configurations different from the configuration of the hydraulic pump drive system 1 according to the first embodiment will be described, and the description of the same configuration will be omitted. The same applies to the hydraulic drive system 1B of the third embodiment and the hydraulic drive system 1C of the fourth embodiment.

In the hydraulic drive system 1A of the second embodiment, the control device 30A has a change rate limiting unit 38A. The change rate limiting unit 38A can change the upper limit change rate according to the first current command value. As described specifically, the rate-of-change limiting unit 38A determines whether or not the first current command value is smaller than a preset current threshold (that is, whether or not the change condition is satisfied). When the rate-of-change limiting unit 38A determines that the first current command value is smaller than the current threshold value (that is, the change condition is satisfied), the rate-of-change limiting unit 38A changes the rate of change of the power shift command value within a preset first upper limit. The power shift command value is limited in the form of a rate. In this embodiment, the change rate of the power shift command value is calculated by the same method as that of the change rate limiting unit 38, but the change rate limiting units 38 and 38A may calculate the power shift command value by a method different from the method described above. The rate of change of the block command value. On the other hand, when the rate-of-change limiting unit 38A determines that the first current command value exceeds the current threshold value (that is, the change condition is not satisfied), the rate-of-change limiting unit 38A prevents the rate of change of the power shift command value from exceeding a predetermined value. The power shift command value is limited in the form of a predetermined second upper limit change rate. In addition, the first upper limit change rate and the second upper limit change rate are preset according to the characteristics of the engine, and can be set as first upper limit change rate>second upper limit change rate or first upper limit change rate<second upper limit change rate any of the.

In this way, when the pump torque of the hydraulic pumps 17L and 17R is increased, the change rate limiting unit 38A can change the upper limit change rate of the power shift command value if the change condition that the first current command value is equal to or greater than the current threshold value is satisfied. . In addition, the change condition does not necessarily need to be the first current command value, and may be changed according to the control time.

In the hydraulic drive system 1A configured as above, the pump torque is suppressed through steps similar to the engine load suppression processing of the hydraulic drive system 1 according to the first embodiment, except for the control in the rate-of-change limiting step S4. Hereinafter, only the specific content of step S4 of the engine load suppression process of the hydraulic drive system 1A will be described. The hydraulic drive system 1A causes the control device 30A to execute the rate-of-change limiting process shown in FIG. 7 in the rate-of-change limiting process as step S4. Hereinafter, the rate-of-change limiting process will be described with reference to FIGS. 7 and 8 . 8 shows a graph sequentially showing changes in the rotational speed, output torque, and power shift command value of the engine E from above, the vertical axis represents various values, and the horizontal axis represents the rotational speed.

In the hydraulic drive system 1A, when the process proceeds to step S4, the rate-of-change limiting process is executed and the process proceeds to step S11. In the current threshold determination step as step S11 , rate-of-change limiting unit 38A determines whether or not the first current command value is smaller than the current threshold. When the rate-of-change limiting unit 38A determines that the first current command value is smaller than the current threshold, the process proceeds to step S12 , and when the rate-of-change limiting unit 38A determines that the first current command value exceeds the current threshold, the process proceeds to step S13 .

In the first rate-of-change limiting process as step S12, the rate-of-change limiting unit 38A calculates the power shift command value, and passes the rate of change so that the rate of change of the power shift command value does not exceed the first upper limit rate of change. Limiting unit 38A limits the power shift command value (see time t1 to t11 in FIG. 8 ). When calculating the power shift command value, the rate-of-change limiting unit 38A outputs the power shift command corresponding to the calculated power shift command value to the power shift valve 20a, and makes the pump torque of the hydraulic pumps 17L, 17R Rise slowly in a slash. When the power shift command value is calculated, the rate-of-change limiting process is terminated and the process proceeds to step S5.

In the second rate-of-change limiting process as step S13, the rate-of-change limiting unit 38A calculates the power shift command value, and passes the rate of change so that the rate of change of the power shift command value does not exceed the second upper limit rate of change. The restriction unit 38A restricts the power shift command (see time t11 to t2 in FIG. 8 ). When the change rate limiting unit 38A has calculated the power shift command value, it outputs the power shift command corresponding to the calculated power shift command value to the power shift valve 20a. With this, the pump torque of the hydraulic pumps 17L, 17R can be rapidly increased. When the power shift command is output, the process proceeds to step S5.

The response speed of the hydraulic pumps 17L and 17R is slow in a low-torque state when the pump torque has just started to increase, but becomes faster as the pump torque increases. In the hydraulic drive system 1A having such a configuration, when the response speed is slow, by reducing the upper limit change rate, the combustion state can be improved and the fuel consumption can be improved. In addition, in the hydraulic drive system 1A, when the response speed is high, the time required for the power shift command value to reach the target current, that is, the time required for the pump torque to reach the target torque can be shortened by increasing the upper limit change rate. . With this, the responsiveness of the hydraulic actuators 11 to 15 to the operating elements can be improved.

Other than that, the hydraulic drive system 1A exhibits the same effects as those of the hydraulic drive system 1 of the first embodiment.

[Third Embodiment]

In the hydraulic drive system 1B, as shown in FIG. 9 , the control device 30B further includes an upper limit limiting unit 39 . The upper limit limiting unit 39 limits the first current command value so that the pump torque of the hydraulic pumps 17L, 17R does not exceed the torque upper limit determined based on the real-time rotational speed of the engine E. In the present embodiment, the upper limit limiting unit 39 sets the current upper limit based on the real-time rotational speed of the engine E, and limits the first current command value so that the first current command value does not exceed the current upper limit.

As described in more detail, the upper limit limiting unit 39 has a plurality of upper limit maps corresponding to the real-time rotational speed of the engine E and the current upper limit, and each upper limit map is determined according to the accelerator level (or the set rotational speed). And the power mode corresponds to each. In addition, the upper limit map is set so that as the real-time rotation speed increases, the current upper limit value decreases, and as the real-time rotation speed decreases, the current upper limit value increases. The upper limit limiting unit 39 determines an upper limit map to be used based on an accelerator level (or a set rotation speed) and a power mode, and uses the determined upper limit map to calculate a current upper limit based on a real-time rotation speed. Furthermore, the upper limit limiting unit 39 limits the first current command value to be equal to or smaller than the calculated current upper limit. The first current command value limited to the current upper limit value in this way is used in the current command subtraction unit 37 together with the reduced current command value calculated by the ESS control unit 36 .

The engine load suppression control of the hydraulic drive system 1B having such a configuration includes a torque limiting process as step S8 as shown in FIG. 10 . The torque limiting process of step S8 is transferred from step S3. In step S8, first, the upper limit limiting unit 39 determines an upper limit map based on the accelerator level (or set rotational speed) and the power mode, and uses the determined upper limit map to calculate the current upper limit value from the real-time rotational speed. . After the calculation, the upper limit limiting unit 39 compares the first current command value with the current upper limit value, and when the first current command value is less than the current upper limit value, the first current command value is not limited, and when the first current command value is When the current upper limit value is greater than or equal to the current upper limit value, the first current command value is increased or decreased while limiting the first current command value to be equal to or less than the current upper limit value. In this way, when the first current command value is limited to the current upper limit value or less, the process proceeds to step S4. In step S4, the rate-of-change limiting unit 38 outputs a power shift command corresponding to the first current command value limited by the upper limit value limiting unit 39 to the power shift valve 20a (refer to the power shift command value in FIG. 11 between the reference rotation speed r2 and the control start rotation speed r1 of the graph), the inclination angle of the swash plate 17b of the hydraulic pumps 17L, 17R is adjusted to an angle corresponding to the power shift command value. With this, the pump torque of the hydraulic pumps 17L, 17R can be suppressed. In addition, in step S7, when the control execution determination part 33 determines that the real-time rotational speed is smaller than the control end rotational speed r3, it transfers to step S8.

In the hydraulic drive system 1B having such a structure, as the load on the engine E decreases and the real-time rotation speed gradually returns to the set rotation speed, the upper limit limiting unit 39 reduces the current upper limit, that is, reduces the torque. Upper limit. Therefore, the pump torque of the hydraulic pumps 17L, 17R can be reduced as the real-time rotation speed gradually returns to the set rotation speed. Also, when the real-time speed is less than the control end speed r3, return from step S7 to step S8, in step S8, the real-time speed changes the torque upper limit value according to the set speed, so even if the operating member is operated in the middle of the speed recovery, the engine E Even if the load suddenly increases and the real-time speed decreases, the pump torque can also be slowly increased from the low torque to the target command torque. With this, it is possible to further suppress an excessive drop in the actual rotational speed of the engine E, and as a result, it is possible to suppress excessive fuel injection at the time of transition.

Other than that, the hydraulic drive system 1B exhibits the same effects as those of the hydraulic drive system 1 of the first embodiment.

[Fourth Embodiment]

The tilt angle adjusting device 20 of the hydraulic drive system 1C shown in FIG. 1 has a horsepower control function of adjusting the tilt angle according to the pump torque of the hydraulic pumps 17L, 17R. More specifically, in the tilt angle adjusting device 20, the pump pressure discharged from the hydraulic pumps 17L and 17R as shown in FIG. tilt angle.

In addition, as shown in FIG. 1 , the hydraulic drive system 1C includes a first pump pressure sensor 51 and a second pump pressure sensor 52 for detecting the pump pressures of the hydraulic pumps 17L and 17R, respectively, and the first pump pressure sensor 51 and the second pump pressure The sensor 52 is a load sensor for detecting the load of the engine E, and outputs a signal corresponding to the pump pressure of the oil pressure pumps 17L, 17R. Moreover, the first pump pressure sensor 51 and the second pump pressure sensor 52 are electrically connected to the control device 30C, and the control device 30C calculates the pressure of the hydraulic pump 17L based on the signals from the first pump pressure sensor 51 and the second pump pressure sensor 52 . , 17R pump pressure.

Also, as shown in FIG. 12 , the control device 30C has a control execution determination unit 33C that uses the pump pressure of the hydraulic pumps 17L, 17R instead of the real-time rotational speed of the engine E to determine whether the pump pressure is less than a threshold value. Specifically, the control execution determination unit 33C has a control start pump pressure calculation map, and in the control start pump pressure calculation map, the average value of the pump pressure corresponds to the control start pump pressure P1. The control execution determination unit 33C sets the control start pump pressure P1 from the control start pump pressure calculation map based on the average value of the pump pressure. Furthermore, the control execution determination unit 33C calculates the pump pressures of the hydraulic pumps 17L, 17R based on the signals from the first pump pressure sensor 51 and the second pump pressure sensor 52 as load sensors, and calculates the pump pressures from the two pump pressures. average value. The control execution determination unit 33C determines whether or not the calculated average value of the pump pressures is equal to or greater than the control start pump pressure P1. The load on the engine E increases when the average value of the pump pressure to be determined increases, and decreases when the average value of the pump pressure decreases. The control execution determination unit 33 determines whether or not the load on the engine E is equal to or greater than a preset control start threshold value by determining whether the average value of the pump pressure is equal to or greater than the control start pump pressure P1. That is, the control execution determination unit 33 determines whether or not the load on the engine E is equal to or greater than the control start threshold value corresponding to the control start pump pressure P1 based on the average value of the pump pressure.

In addition, the control execution determination unit 33C has a control end pump pressure calculation map in which the average value of the pump pressure corresponds to the control end pump pressure P3 (control end threshold value). The control execution determination unit 33C sets the control end pump pressure P3 from the control end pump pressure calculation map based on the average value of the pump pressure. Furthermore, control execution determination unit 33C calculates the pump pressures of hydraulic pumps 17L and 17R based on the signals from first pump pressure sensor 51 and second pump pressure sensor 52 , and calculates their average value from the two pump pressures. In addition, the control execution determination unit 33C determines whether or not the calculated average value of the pump pressures is equal to or greater than the control end pump pressure P3. Since the above-mentioned relationship exists between the average value of the pump pressure and the load on the engine E, the control execution determination unit 33 determines whether the average value of the pump pressure is equal to or greater than the control end pump pressure P3, thereby determining whether the load on the engine E is Control ends above the threshold. That is, the control execution determination unit 33 determines based on the pump pressure whether or not the load on the engine E is equal to or greater than the control end threshold value corresponding to the control end pump pressure P3.

In addition, the determination result in the control execution determination unit 33 is used in the current command value selection unit 34 together with the target current and the standby current, and the current command value selection unit 34 selects any one of the target current and the standby current as the current based on the determination result. The first current command value.

In addition, the control device 30C further includes an upper limit limiting unit 39C. The upper limit limiting unit 39C limits the pump torque of the hydraulic pumps 17L, 17R so as not to exceed the torque upper limit determined based on the average value of the pump pressure. In the present embodiment, the upper limit limiting unit 39C sets the current upper limit based on the average value of the two pump pressures, and limits the power shift command value so that the current upper limit does not exceed the current upper limit.

In more detail, the upper limit limiting unit 39C has an upper limit map in which the average value of the pump pressure and the current upper limit are associated. In addition, in the upper limit value map, in the non-horsepower control state in which the average value of the pump pressure is lowered, the current upper limit value is set based on the average value of the pump pressure. Specifically, the upper limit map is set so that the current upper limit increases as the average value of the pump pressure increases. The non-horsepower control state refers to the following state: in the case of a negative control system, the pump pressures of the hydraulic pumps 17L and 17R are small, and the tilt angle determined by the negative control pressure is smaller _than the tilt angle determined by the power shift pressure p1 , so the servo mechanism 20b controls the inclination angle of the swash plate 17b according to the negative control pressure. In addition, the non-horsepower control state in the case of the electric positive control system refers to a state in which the flow command value determined by the pilot pressure of the remote control valve is smaller than the target pump horsepower limit value. In the upper limit value map, the average value of the pump pressure is such that the torque upper limit value does not drop too much and the inclination angle of the swash plate 17b is not determined by the power shift pressure p1 in such _a non-horsepower control state. The value corresponds to the torque upper limit (specifically, the current upper limit), and the upper limit limiting unit 39C calculates the current upper limit from the upper limit map based on the average value of the pump pressure. Furthermore, upper limit limiting unit 39C limits the first current command value to be equal to or smaller than the calculated current upper limit. The first current command value thus limited to the current upper limit value or less is used in the current command subtraction unit 37 together with the reduced current command value calculated in the ESS control unit 36 .

In the engine load suppression control of the hydraulic drive system 1C having such a structure, as shown in FIG. The third pump pressure determination process of S11. The process proceeds from step S1 to the first pump pressure determination process of step S9, in which the control execution determination unit 33C determines whether or not the average value of the pump pressure is equal to or greater than the control start pump pressure P1. In detail, the control execution determination unit 33C sets the control start pump pressure P1 from the control start pump pressure calculation map based on the average value of the pump pressures, and determines whether the average value of the pump pressures is equal to or greater than the control start pump pressure P1. When the control execution determination unit 33C determines that the average value is smaller than the control start pump pressure P1, it returns to step S1 and continues to output the power shift command corresponding to the standby current from the control device 30 to the power shift valve 20a. That is, the pump torque of the hydraulic pumps 17L and 17R is maintained at the standby torque until the average value of the pump pressure reaches the control start pump pressure P1 or higher. On the other hand, when the control execution determination unit 33C determines that the average value of the pump pressure is equal to or greater than the control start pump pressure P1, the process proceeds to step S3, and the current switching process is executed in step S3.

When the rate-of-change limiting unit 38 determines in step S6 that the power shift command value has reached the target current, the process proceeds to a second pump pressure determination step in step S10 . In step S10 , the control execution determination unit 33C determines whether or not the average value of the pump pressure is equal to or greater than the control end pump pressure P3 . When the control execution determination unit 33C determines that the average value is equal to or greater than the control end pump pressure P3, the current command value selection unit 34 continues to select the target current as the first current command value, and returns to step S8. On the other hand, when the average value of the pump pressure is less than the control end pump pressure P3, the process returns to step S1, and the first current command value is switched from the target current to the standby current by the control execution determination unit 33 . With this, the power shift command value is reduced to the standby current, and the pump torque of the hydraulic pumps 17L, 17R is reduced to the necessary minimum torque.

Moreover, in the torque limiting process as step S8, first, the upper limit limiting unit 39C calculates the current upper limit from the upper limit map based on the pump average pressure. After the calculation, the upper limit limiting unit 39C compares the first current command value with the current upper limit value, and when the first current command value is smaller than the current upper limit value, the power shift command value is not limited, and the first current command value When it is equal to or greater than the current upper limit value, the power shift command value is increased or decreased while limiting the power shift command value to be equal to or less than the current upper limit value. After increasing or decreasing while limiting the first current command value to be equal to or less than the current upper limit value in this way, the process proceeds to step S4, and a change rate limiting process is executed in step S4. In step S4, the change rate limiting unit 38 outputs a power shift command corresponding to the first current command value limited by the upper limit value limiting unit 39 to the power shift valve 20a (see the graph of the pump torque in FIG. 14 ), and the inclination angle of the swash plate 17b of the hydraulic pumps 17L, 17R is adjusted to an angle corresponding to the power shift command value. With this, the pump torque of the hydraulic pumps 17L, 17R can be suppressed.

In addition, in the ESS control process as step S5, it is judged whether or not to execute the ESS control by judging whether the real-time rotation speed calculated based on the signal from the rotation speed sensor 22 is smaller than the reference rotation speed r2. Here, the reference rotation speed r2 is set as the real-time rotation speed at which the average value of the pump pressure is equal to or higher than the control end pump pressure P3, that is, the engine load is greater than the control start threshold value, and is set to the same value as the first embodiment to the third embodiment. The reference rotational speed r2 of the embodiment is the same. With this, the ESS control is executed when a load greater than that of the engine E is applied to the engine E and the real-time rotational speed of the engine E becomes smaller than the reference rotational speed r2. With this, when the load on the engine E increases so that the real-time rotational speed is lower than the reference rotational speed r2, the pump torques of the hydraulic pumps 17L and 17R can be gradually reduced as the real-time rotational speed drops (refer to less than at engine speed r2).

In the hydraulic drive system 1C having such a configuration, the pump pressure of the hydraulic pumps 17L, 17R decreases as the load on the hydraulic pumps 17L, 17R decreases, and the upper limit limiting unit 39 decreases the current upper limit, That is, reduce the torque upper limit value. Moreover, when the average value of pump pressure is equal to or more than control end pump pressure P3, it returns to step S8 from step S10. Therefore, even in a situation where the pump pressure of the hydraulic pumps 17L, 17R is suddenly increased by operating the operating member in the middle of the pump pressure drop, and the load on the engine E increases again, the pump torque can be gradually increased from the low torque. to the target command torque. With this, an excessive drop in the real-time rotational speed of the engine E can be further suppressed.

In addition, in the hydraulic drive system 1C, the first pump pressure sensor 51 and the second pump pressure sensor 52 can indirectly detect the change in the load of the engine E from the change in the pump pressure of the hydraulic pumps 17L, 17R. That is, in the hydraulic drive system 1C, the pump torque can be controlled based on the detected pump pressure, and the control can be performed based on the pump pressure that can quickly reflect fluctuations in the pump load. Therefore, the responsiveness to the load fluctuation of the engine E can be improved, the sudden increase of the load on the engine E can be further suppressed, and excessive fuel injection at the time of transition can be suppressed.

In the present embodiment, the average value of the pump pressures of the hydraulic pumps 17L and 17R is used in the engine load suppression process, but the average value does not necessarily need to be the average value. In particular, in the case of a system capable of independently controlling the pump torques of the two hydraulic pumps 17L, 17R, each pump torque upper limit value may be limited according to the pump pressure of each hydraulic pump 17L, 17R.

Other than that, the hydraulic drive system 1C exhibits the same effects as those of the hydraulic drive system 1 of the first embodiment.

[Other Embodiments]

In the hydraulic pump driving systems 1, 1A, 1B, and 1C of the present embodiment, the power shift command value is increased in a ramp by the rate-of-change limiting unit 38, but it does not necessarily have to be increased in a ramp. Curved or first-order lag-like rise. Also, in the hydraulic pump drive systems 1, 1A, 1B, and 1C of the present embodiment, the hydraulic actuators 11-15 are driven by the two hydraulic pumps 17L, 17R, but one hydraulic pump may be used. Also, the input means for setting the set rotational speed does not necessarily need to be an accelerator dial, and may be an accelerator pedal or an accelerator lever.

Also, in the hydraulic pump drive systems 1, 1A, 1B, and 1C of the present embodiment, an example using a hydraulic negative control system was described, but an electric positive control system that calculates pump torque electrically may also be used.

In the hydraulic drive system 1C of the fourth embodiment, the control device 30C includes the upper limit limiting unit 39C, but it is not necessary to necessarily include the upper limit limiting unit 39C.

Also, the construction machines to which the hydraulic pump driving systems 1, 1A, 1B, and 1C are installed are not limited to hydraulic excavators, and may be other construction machines such as cranes and bulldozers, as long as they are equipped with hydraulic actuators. Also, in the hydraulic pump driving systems 1 , 1A, 1B, and 1C, the hydraulic pump is given as an example of the hydraulic pump, but the hydraulic pump is not limited to the hydraulic pump, and any pump may discharge liquid such as water.

Claims (8)

1. a kind of fluid power system, possesses：

Engine, the action of the engine is in the form of the setting speed rotation driving being preset by apparatus for controlling speed Control；

The hydraulic pump of the variable capacity type of discharge pressure liquid by the engine rotation driving；

The variable displacement mechanism for the pump running torque for changing the discharge capacity of the hydraulic pump and adjusting the hydraulic pump；

For the load sensor for the load for detecting the engine；With

The action of the variable displacement mechanism is controlled, so that the pump running torque of the hydraulic pump reaches target instruction target word set in advance and turned The form of square changes the control device of the discharge capacity of the hydraulic pump；

The control device based on the testing result that is detected by the load sensor judge the engine load whether be Control starts more than threshold value, when the load of the engine reaches more than control beginning threshold value set in advance, passes through control The action of the variable displacement mechanism, make the pump running torque of the hydraulic pump with the rate of change below upper limit rate of change set in advance The target instruction target word torque is risen to from the standby torque less than the target instruction target word torque.

2. fluid power system according to claim 1, it is characterised in that

The hydraulic pump changes discharge capacity by adjusting its tilt angle；

The variable displacement mechanism is had the servo control mechanism for the tilt angle for switching the hydraulic pump and moved based on what is inputted Power shifting commands adjust the control valve of the servo control mechanism；

There is the control device target current calculating part, standby current calculating part, current instruction value selector, control execution to sentence Determine portion and rate of change limiting unit；

The target current calculating part is in order that the pump running torque of the hydraulic pump reaches the target instruction target word torque, and calculates work For the target current of the current instruction value to the control valve should be inputted；

The standby current calculating part is in order that the pump running torque of the hydraulic pump reaches the standby torque, and is calculated as answering Input to the standby current of the current instruction value of the control valve；

The current instruction value selector, perform determination unit in the control and be determined as that the load of the engine is less than the control When system starts threshold value, the standby current for selecting to be calculated by the standby current calculating part is as the current instruction value, and in institute When stating the load for controlling execution determination unit to judge the engine to be more than the control beginning threshold value, select electric by the target The target current that stream calculation portion calculates is as the current instruction value；

The rate of change limiting unit, which calculates, is limited in the rate of change of the current instruction value below the upper limit rate of change Power shifting command value, and the power shifting instruction corresponding with the power shifting command value is exported to the control Valve processed.

3. fluid power system according to claim 1 or 2, it is characterised in that

The control device when making the pump running torque of the hydraulic pump rise to the target instruction target word torque from the standby torque, If meeting change condition set in advance, the upper limit rate of change can be changed.

4. fluid power system according to claim 2, it is characterised in that

The control device sets the torque upper limit value corresponding with the testing result detected in the load sensor, and When changing the pump running torque of the hydraulic pump between the standby torque and the target instruction target word torque, by the pump of the hydraulic pump Torque limit is below the torque upper limit value.

5. fluid power system according to claim 2, it is characterised in that

The load sensor includes the speed probe for being used to detect the real-time rotating speed of the engine；

The control performs determination unit and judges the engine based on the rotating speed in real time detected in the speed probe Whether load, which reaches the control, starts more than threshold value.

6. fluid power system according to claim 5, it is characterised in that

The control device is formed as structure：

When the real-time rotating speed detected by the speed probe is less than reference rotation speed, based on rotating speed and the institute in real time The pump running torque that the speed discrepancy between setting speed reduces the hydraulic pump is stated, the reference rotation speed is less than starts threshold with the control It is worth corresponding control and starts rotating speed.

7. fluid power system according to claim 2, it is characterised in that

The load sensor includes pump pressure sensor of the detection as the pump pressure of the discharge pressure of the hydraulic pump；

The control performs determination unit and judges the negative of the engine based on the pump pressure detected by the pump pressure sensor Whether lotus, which reaches the control, starts more than threshold value.

8. fluid power system according to claim 7, it is characterised in that

The load sensor includes the speed probe for being used to detect the real-time rotating speed of the engine；

The control device is when the real-time rotating speed detected by the speed probe is less than reference rotation speed, based on described The speed discrepancy between rotating speed and the setting speed reduces the pump running torque of the hydraulic pump in real time；

What the reference rotation speed was set as that the load of the engine is more than that the control starts in the state of threshold value described starts The rotating speed of machine.