Construction machine

Abstract

Provided is a construction machine that can further improve the energy consumption rate of a prime mover by using regenerative energy.　A shovel according to the present invention comprises: a swing hydraulic motor; a hydraulic pump that, together with the swing hydraulic motor, constitutes a closed circuit; a prime mover that drives the hydraulic pump; an operation device that provides instruction for operation of the swing hydraulic motor; a controller that controls the discharge direction and capacity of the hydraulic pump in accordance with the instruction from the operation device; an accumulator that stores pressurized oil; and an assist valve that is disposed in an oil passage between the accumulator and the swing hydraulic motor. The controller determines whether the swing hydraulic motor is accelerating, and when it is determined that the swing hydraulic motor is accelerating, the controller controls the assist valve to supply pressurized oil from the accumulator to the swing hydraulic motor and limit the capacity of the hydraulic pump.

Description

Construction Machinery

[0001] The present invention relates to a construction machine such as an excavator.

[0002] In construction machines such as excavators, there is known a configuration that uses pressure oil discharged from, for example, a hydraulic actuator as regenerative energy to improve the energy consumption rate (specifically, the fuel consumption rate or the electricity consumption rate) of a prime mover (specifically, an engine or an electric motor).

[0003] The excavator of Patent Document 1 includes a dedicated assist hydraulic motor mechanically coupled to a prime mover. This hydraulic motor is driven by pressure oil discharged from a hydraulic actuator (specifically, a boom hydraulic cylinder or a swing hydraulic motor) to assist the prime mover. This reduces the load on the prime mover and improves the energy consumption rate of the prime mover.

[0004] Japanese Unexamined Patent Publication No. 2019-94608

[0005] Although the excavator of Patent Document 1 includes a dedicated assist hydraulic motor, pressure oil is not always supplied to this hydraulic motor. In a state where no pressure oil is supplied to the dedicated assist hydraulic motor, the dedicated assist hydraulic motor causes dragging loss, which increases the load on the prime mover. As a result, part of the effect of improving the energy consumption rate of the prime mover is offset.

[0006] An object of the present invention is to provide a construction machine capable of further improving the energy consumption rate of a prime mover by using regenerative energy.

[0007] To achieve the above objective, the present invention provides a construction machine comprising a hydraulic motor, a hydraulic pump that forms a closed circuit together with the hydraulic motor, a prime mover for driving the hydraulic pump, an operating device for instructing the operation of the hydraulic motor, and a controller for controlling the discharge direction and capacity of the hydraulic pump in accordance with the instructions of the operating device, wherein the machine further comprises an accumulator for storing pressurized oil and an assist valve arranged in the oil passage between the accumulator and the hydraulic motor, the controller determines whether the hydraulic motor is accelerating, and if it determines that the hydraulic motor is accelerating, controls the assist valve to supply pressurized oil from the accumulator to the hydraulic motor and limits the capacity of the hydraulic pump.

[0008] According to the present invention, the energy consumption rate of the prime mover can be further improved by utilizing regenerative energy.

[0009] This is a side view showing the structure of an excavator in the first embodiment of the present invention. This is a diagram showing the configuration of the excavator drive system in the first embodiment of the present invention. This is a block diagram showing the functional configuration of the controller in the first embodiment of the present invention. This is a diagram showing the change over time of the operating amount of the operating lever of the operating device, the speed of the swing hydraulic motor, the pressure of the accumulator, the pressure on the meter-in side of the swing hydraulic motor, the opening degree of the assist valve, and the volume of the hydraulic pump in the first embodiment of the present invention. This is a diagram showing the configuration of the excavator drive system in the second embodiment of the present invention. This is a block diagram showing the functional configuration of the controller in the second embodiment of the present invention. This is a diagram showing the configuration of the excavator drive system in one modified example of the present invention.

[0010] A first embodiment of the present invention will be described with reference to the drawings.

[0011] Figure 1 is a side view showing the structure of the shovel in this embodiment.

[0012] The excavator comprises a mobile body 1 and a slewing body 2 that is rotatably mounted above the mobile body 1. The mobile body 1 moves by the drive of a hydraulic motor for travel (not shown), and the slewing body 2 rotates by the drive of a hydraulic motor for rotation 3 (see Figure 2, described later).

[0013] The excavator is equipped with a working device 4 connected to a slewing body 2. The working device 4 comprises a boom 5 rotatably connected to the slewing body 2, an arm 6 rotatably connected to the boom 5, and a bucket 7 rotatably connected to the arm 6. The boom 5 rotates by the drive of a boom hydraulic cylinder 8, the arm 6 rotates by the drive of an arm hydraulic cylinder 9, and the bucket 7 rotates by the drive of a bucket hydraulic cylinder 10.

[0014] The slewing body 2 is equipped with a driver's cab 11 in which an operator sits. Inside the driver's cab 11 are an operating device (not shown) that instructs the operation of the travel hydraulic motor (and consequently the travel of the travel body 1), an operating device 12A (see Figure 2 below) that instructs the operation of the slewing hydraulic motor 3 (and consequently the slewing body 2) and the operation of the arm hydraulic cylinder 9 (and consequently the rotation of the arm 6), and an operating device 12B (see Figure 2 below) that instructs the operation of the boom hydraulic cylinder 8 (and consequently the rotation of the boom 5) and the operation of the bucket hydraulic cylinder 10 (and consequently the rotation of the bucket 7).

[0015] The excavator is equipped with a drive system that drives the aforementioned hydraulic actuators (specifically, a travel hydraulic motor, a slewing hydraulic motor 3, a boom hydraulic cylinder 8, an arm hydraulic cylinder 9, and a bucket hydraulic cylinder 10) in response to instructions from the aforementioned operating devices.

[0016] Figure 2 is a diagram showing the configuration of the excavator drive system in this embodiment. Note that Figure 2 shows the configuration of the slewing hydraulic motor 3, boom hydraulic cylinder 8, and arm hydraulic cylinder 9 of the excavator drive system, and the illustration and explanation of the configuration of other hydraulic actuators are omitted.

[0017] The excavator's drive system includes a hydraulic pump 13 that forms a closed circuit together with the slewing hydraulic motor 3, a regulator 14 that varies the discharge direction and capacity of the hydraulic pump 13 by varying the tilt angle of the swash plate or tilt axis of the hydraulic pump 13, a hydraulic pump 15 that forms an open circuit together with the boom hydraulic cylinder 8 and the arm hydraulic cylinder 9, a control valve 16A that controls the flow of pressurized oil from the hydraulic pump 15 to the boom hydraulic cylinder 8, a control valve 16B that controls the flow of pressurized oil from the hydraulic pump 15 to the arm hydraulic cylinder 9, a regulator 17 that varies the capacity of the hydraulic pump 15 by varying the tilt angle of the swash plate or tilt axis of the hydraulic pump 15, and a controller 18 that controls the regulator 14, control valves 16A and 16B, and the regulator 17 according to instructions from the operating devices 12A and 12B. The hydraulic pumps 13 and 15 are driven by power transmitted from the prime mover 20 via a power transmission device 19. In this embodiment, the prime mover 20 is an engine, but it may also be an electric motor.

[0018] Although not shown in detail, the operating device 12A includes an operating lever that can be operated by an operator in the forward / backward and left / right directions, a potentiometer that generates and outputs a first instruction signal corresponding to the amount of operation on the front side of the operating lever or a second instruction signal corresponding to the amount of operation on the rear side of the operating lever, and a potentiometer that generates and outputs a third instruction signal corresponding to the amount of operation on the left side of the operating lever or a fourth instruction signal corresponding to the amount of operation on the right side of the operating lever.

[0019] Although not shown in detail, the operating device 12B includes an operating lever that can be operated by an operator in the forward / backward and left / right directions, and a potentiometer that generates and outputs a fifth instruction signal corresponding to the amount of operation of the front side of the operating lever, or a sixth instruction signal corresponding to the amount of operation of the rear side of the operating lever.

[0020] Although not shown in detail, the controller 18 includes a processor that executes processing according to a program, and memory for storing programs and data.

[0021] When the controller 18 receives a first instruction signal from the operating device 12A, it controls the regulator 14 to change the discharge direction of the hydraulic pump 13 to one side (left side in the diagram) and to vary the capacity of the hydraulic pump 13 according to the first instruction signal. This causes the hydraulic pump 13 to supply pressurized oil to one side (left side in the diagram) of the slewing hydraulic motor 3, causing the slewing hydraulic motor 3 to rotate in one direction and controlling the rotational speed. As a result, the slewing body 2 is rotated to the right and the slewing speed is controlled.

[0022] When the controller 18 receives a second instruction signal from the operating device 12A, it controls the regulator 14 to change the discharge direction of the hydraulic pump 13 to the other side (right side in the diagram) and to vary the capacity of the hydraulic pump 13 according to the second instruction signal. This causes the hydraulic pump 13 to supply pressurized oil to the other side (right side in the diagram) of the slewing hydraulic motor 3, causing the slewing hydraulic motor 3 to rotate in the other direction and controlling its rotational speed. As a result, the slewing body 2 is rotated to the left and its rotational speed is controlled.

[0023] When the controller 18 receives a third or fourth instruction signal from the operating device 12A, it generates a corresponding control signal and outputs it to the solenoid section on one or the other side of the control valve 16B, switching the control valve 16B from the neutral position to the switching position on one or the other side. This causes the hydraulic pump 15 to supply pressurized oil to the rod side or bottom side of the arm hydraulic cylinder 9 via the control valve 16B, thereby shortening or extending the arm hydraulic cylinder 9. As a result, the arm 6 is dumped or clouded.

[0024] When the controller 18 receives a fifth or sixth instruction signal from the operating device 12B, it generates a corresponding control signal and outputs it to the solenoid section on one or the other side of the control valve 16A, switching the control valve 16A from the neutral position to the switching position on one or the other side. This causes the hydraulic pump 15 to supply pressurized oil to the rod side or bottom side of the boom hydraulic cylinder 8 via the control valve 16A, thereby shortening or extending the boom hydraulic cylinder 8. As a result, the boom 5 is lowered or raised.

[0025] If no third, fourth, fifth, or sixth instruction signals are input from the operating devices 12A or 12B, the controller 18 controls the regulator 17 to control the capacity of the hydraulic pump 15 to a predetermined minimum value. On the other hand, if any of the third, fourth, fifth, or sixth instruction signals are input from the operating devices 12A or 12B, the controller 18 controls the regulator 17 to vary the capacity of the hydraulic pump 15 according to the instruction signal.

[0026] The excavator's drive system includes relief valves 22A and 22B that define the upper limit pressure of the closed circuit described above (specifically, the oil passages 21A and 21B connecting the swing hydraulic motor 3 and the hydraulic pump 13), a flushing valve 23 that discharges excess pressurized oil from the closed circuit, a relief valve 22C that defines the upper limit pressure of the oil passage 21C connected to the discharge side of the relief valves 22A and 22B and the flushing valve 23, a charge pump 24 that supplies pressurized oil to the oil passage 21C, and makeup valves 25A and 25B that replenish pressurized oil from the oil passage 21C to the oil passages 21A and 21B.

[0027] The excavator's drive system includes an accumulator 26 for storing pressurized oil, a regenerative valve 27 provided in the oil passage connecting the bottom side of the boom hydraulic cylinder 8 to the accumulator 26, and an assist valve 28 (a three-position switching valve in this embodiment) provided in the oil passage connecting the accumulator 26 to a closed circuit. When a fifth instruction signal is input from the operating device 12B (in other words, when the boom 5 is lowered), the controller 18 switches the regenerative valve 27 from the closed state to the open state. As a result, the accumulator 26 takes in pressurized oil discharged from the bottom side of the boom hydraulic cylinder 8 and stores it as regenerative energy.

[0028] A key feature of this embodiment is that the controller 18 determines whether the swing hydraulic motor 3 is accelerating. If it determines that the swing hydraulic motor 3 is accelerating, it controls the assist valve 28 to supply pressurized oil from the accumulator 26 to the swing hydraulic motor 3 and limits the capacity of the hydraulic pump 13. The functions of this controller 18 will be explained using Figure 3. Figure 3 is a block diagram showing the functional configuration of the controller 18 in this embodiment.

[0029] The controller 18 has a functional configuration that includes a target capacity calculation unit 31, a rate limiter 32, a target capacity limiting unit 33, an acceleration determination unit 34, and a gain generator 35.

[0030] The target capacity calculation unit 31 of the controller 18 stores the relationship between the instruction signal and the target capacity in advance, and uses this relationship to calculate the target capacity of the hydraulic pump 13 corresponding to the first or second instruction signal from the operating device 12A. The rate limiter 32 outputs the target capacity calculated by the target capacity calculation unit 31, limiting its increase or decrease rate so that the absolute value is less than or equal to a set value. The target capacity limiting unit 33, when the judgment value of the acceleration judgment unit 34 (described later) is "0", leaves the target capacity from the rate limiter 32 as is and outputs a corresponding control signal to the regulator 14. The rate limiter 32 is intended to delay the responsiveness of the hydraulic pump 13's capacity change. This is because the inertial force of the slewing body 2 is large, which takes time for the flow rate of the slewing hydraulic motor 3 to change.

[0031] The acceleration determination unit 34 of the controller 18 determines whether the swing hydraulic motor 3 is accelerating in one direction or the other, based on the change in the target capacity of the hydraulic pump 13 from the rate limiter 32. If it determines that the swing hydraulic motor 3 is accelerating in one direction or the other, it outputs a determination value of "1", and if it determines that the swing hydraulic motor 3 is not accelerating, it outputs a determination value of "0". The gain generator 35 outputs a control signal to the assist valve 28 when the determination value of the acceleration determination unit 34 is "1", and does not output a control signal to the assist valve 28 when the determination value of the acceleration determination unit 34 is "0".

[0032] As explained using Figure 2 above, when the controller 18 determines that the swing hydraulic motor 3 is accelerating in one direction, it outputs a control signal to the solenoid section on one side (left side in the figure) of the assist valve 28, and switches the assist valve 28 from the neutral position to the switching position on one side (left side in the figure). As a result, pressurized oil is supplied from the accumulator 26 to one side of the swing hydraulic motor 3 via the assist valve 28, thereby assisting the driving of the swing hydraulic motor 3.

[0033] When the controller 18 determines that the swing hydraulic motor 3 is accelerating in another direction, it outputs a control signal to the solenoid section on the other side (right side in the diagram) of the assist valve 28, switching the assist valve 28 from the neutral position to the switching position on the other side (right side in the diagram). This supplies pressurized oil from the accumulator 26 to the other side of the swing hydraulic motor 3 via the assist valve 28, thereby assisting the driving of the swing hydraulic motor 3.

[0034] Returning to Figure 3, the target capacity limiting unit 33 of the controller 18 limits the target capacity from the rate limiter 32 when the determination value of the acceleration determination unit 34 is "1", and outputs a corresponding control signal to the regulator 14. In this embodiment, the target capacity limiting unit 33 delays the start timing of the increase in the capacity of the hydraulic pump 13 by a predetermined time, thereby reducing the flow rate of the hydraulic pump 13 overall.

[0035] Next, the operation and effects of this embodiment will be explained using Figure 4. Figure 4 is a diagram showing the changes over time of the operating amount of the operating lever of the operating device 12A, the speed of the slewing hydraulic motor 3, the pressure of the accumulator 26, the pressure on the meter-in side of the slewing hydraulic motor 3, the opening degree of the assist valve 28, and the volume of the hydraulic pump 13 in this embodiment.

[0036] As shown in Figure 4, the operator starts operating the control lever of the control device 12A (time t1), and then maintains the amount of operation of the control lever at a predetermined value (e.g., the maximum value). As a result, the slewing hydraulic motor 3 accelerates and then maintains the predetermined speed (from time t2 onward).

[0037] The controller 18 determines that the swing hydraulic motor 3 is accelerating between times t1 and t2, and switches the assist valve 28 from the neutral position to the switching position for one side or the other side. This supplies pressurized oil from the accumulator 26 to one side or the other side of the swing hydraulic motor 3 via the assist valve 28, thereby assisting the driving of the swing hydraulic motor 3. The controller 18 also limits the capacity of the hydraulic pump 13 as shown by the solid line A in Figure 4.

[0038] As a comparative example, consider the case where the pressurized oil from the accumulator 26 is not supplied to the swing hydraulic motor 3, and the capacity of the hydraulic pump 13 is not limited as shown by the dotted line B in Figure 4. In this embodiment, compared to the comparative example, the flow rate of the hydraulic pump 13 during acceleration of the swing hydraulic motor 3 can be reduced, thereby reducing the load on the prime mover 20.

[0039] Furthermore, in this embodiment, the excavator does not have a dedicated assist hydraulic motor as described in Patent Document 1. Therefore, the load on the prime mover 20 can be reduced compared to the case in which a dedicated assist hydraulic motor is provided. In addition, in this embodiment, during the acceleration of the swing hydraulic motor 3, the pressurized oil stored in the accumulator 26 is used as regenerative energy to provide assistance. Therefore, the frequency of assistance can be increased compared to the case in which no assistance is provided during the acceleration of the swing hydraulic motor 3, and the load on the prime mover 20 can be reduced.

[0040] Based on the above, in this embodiment, the energy consumption rate of the prime mover 20 can be further improved by utilizing regenerative energy.

[0041] A second embodiment of the present invention will be described with reference to the drawings. In this embodiment, parts equivalent to those in the first embodiment are denoted by the same reference numerals, and their descriptions are omitted as appropriate.

[0042] Figure 5 is a diagram showing the configuration of the excavator drive system in this embodiment.

[0043] In this embodiment, the excavator drive system includes a pressure sensor 29 (first pressure sensor) that detects the pressure of the accumulator 26, and pressure sensors 30A and 30B (second pressure sensors) that detect the pressure on one side and the other side of the swing hydraulic motor 3.

[0044] The controller 18 determines, based on detection results from pressure sensors 29, 30A, 30B, whether the pressure of the accumulator 26 is higher than the pressure on the meter-in side of the swing hydraulic motor 3. When the swing hydraulic motor 3 is accelerating and the pressure of the accumulator 26 is higher than the pressure on the meter-in side of the swing hydraulic motor 3, the controller 18 controls the assist valve 28 to supply pressure oil from the accumulator 26 to the swing hydraulic motor 3, and limits the displacement of the hydraulic pump 13. The function of such controller 18 will be described with reference to FIG. 6. FIG. 6 is a block diagram showing the functional configuration of the controller 18 in the present embodiment.

[0045] As a functional configuration, the controller 18 includes a target displacement calculation unit 31, a rate limiter 32, a target displacement limiting unit 33, an acceleration determination unit 34, a gain generator 35, a pressure difference calculation unit 36, a pressure difference determination unit 37, and an AND circuit 38.

[0046] The pressure difference calculation unit 36 calculates a difference (pressure difference) between the pressure of the accumulator 26 detected by the pressure sensor 29 and the pressure on the meter-in side of the swing hydraulic motor 3 detected by the pressure sensor 30A or 30B. When the pressure difference calculated by the pressure difference calculation unit 36 is equal to or greater than a predetermined value, the pressure difference determination unit 37 outputs a determination value "1", and when the pressure difference calculated by the pressure difference calculation unit 36 is less than the predetermined value, the pressure difference determination unit 37 outputs a determination value "0".

[0047] The AND circuit 38 outputs a determination value "1" when both the determination value of the acceleration determination unit 34 and the determination value of the pressure difference determination unit 37 are "1", and outputs a determination value "0" when at least one of the determination value of the acceleration determination unit 34 and the determination value of the pressure difference determination unit 37 is "0". The gain generator 35 outputs a control signal to the assist valve 28 when the determination value of the AND circuit 38 is "1", and does not output a control signal to the assist valve 28 when the determination value of the AND circuit 38 is "0".

[0048] Also in the present embodiment configured as described above, similar to the first embodiment, the energy consumption rate of the prime mover 20 can be further improved by using regenerative energy. In addition, in the present embodiment, during acceleration of the swing hydraulic motor 3, if the pressure of the accumulator 26 is higher than the pressure on the meter-in side of the swing hydraulic motor 3, pressurized oil is supplied from the accumulator 26 to the swing hydraulic motor 3. Therefore, pressurized oil can be stably supplied to the swing hydraulic motor 3.

[0049] It should be noted that, in the first and second embodiments, the case where the assist valve 28 is configured by one three-position switching valve has been described as an example, but the present invention is not limited thereto. For example, as shown in FIG. 7, the assist valve 28 may be configured by two two-position switching valves.

[0050] In addition, in the first and second embodiments, the case where the controller 18 delays the increase start timing of the displacement of the hydraulic pump 13 by a predetermined time as a restriction on the displacement of the hydraulic pump 13 has been described as an example, but the present invention is not limited thereto. The controller 18 may change the increase rate of the displacement of the hydraulic pump 13 stepwise or continuously to reduce the flow rate of the hydraulic pump 13 as a whole.

[0051] In addition, in the first and second embodiments, the case where the accumulator 26 accumulates pressurized oil discharged from the boom hydraulic cylinder 8 has been described as an example, but the present invention is not limited thereto. The accumulator 26 may accumulate pressurized oil discharged from a hydraulic actuator other than the boom hydraulic cylinder 8, or may accumulate pressurized oil discharged from a hydraulic pump.

[0052] It should be noted that, in the above description, the case where the present invention is applied to a configuration related to a swing hydraulic motor of an excavator has been described as an example, but the present invention is not limited thereto. That is, the present invention may be applied to construction machinery other than excavators, and may also be applied to a configuration related to a hydraulic motor other than a swing hydraulic motor.

[0053] 3. Swivel hydraulic motor 12A. Operating device 13. Hydraulic pump 18. Controller 20. Prime mover 26. Accumulator 28. Assist valve 29. Pressure sensor (first pressure sensor) 30A, 30B. Pressure sensor (second pressure sensor)

Claims

1. A construction machine comprising a hydraulic motor, a hydraulic pump that forms a closed circuit together with the hydraulic motor, a prime mover that drives the hydraulic pump, an operating device that instructs the operation of the hydraulic motor, and a controller that controls the discharge direction and capacity of the hydraulic pump in accordance with the instructions of the operating device, wherein the machine further comprises an accumulator for storing pressurized oil and an assist valve arranged in the oil passage between the accumulator and the hydraulic motor, and the controller determines whether the hydraulic motor is accelerating, and if it determines that the hydraulic motor is accelerating, controls the assist valve to supply pressurized oil from the accumulator to the hydraulic motor and limits the capacity of the hydraulic pump.

2. A construction machine according to claim 1, comprising: a first pressure sensor for detecting the pressure of the accumulator; and a second pressure sensor for detecting the pressure of the hydraulic motor, wherein the controller determines, based on the detection results of the first and second pressure sensors, whether the pressure of the accumulator is higher than the pressure on the meter-in side of the hydraulic motor; and, if the hydraulic motor is accelerating and the pressure of the accumulator is higher than the pressure on the meter-in side of the hydraulic motor, controls the assist valve to supply pressurized oil from the accumulator to the hydraulic motor and limits the capacity of the hydraulic pump.

3. The construction machine according to claim 1, wherein the controller delays the timing of the start of increasing the capacity of the hydraulic pump by a predetermined time as a limit on the capacity of the hydraulic pump.

4. A construction machine according to claim 1, wherein the controller calculates a target capacity of the hydraulic pump corresponding to an instruction signal from the operating device, limits the calculated target capacity such that the absolute value of its increase or decrease rate is less than or equal to a set value, and determines whether the hydraulic motor is accelerating based on the change in the limited target capacity.

Images