EP4012114A1

EP4012114A1 - Excavator

Info

Publication number: EP4012114A1
Application number: EP20849164.7A
Authority: EP
Inventors: Yoshiyasu Itsuji
Original assignee: Sumitomo Heavy Industries Ltd
Current assignee: Sumitomo Heavy Industries Ltd
Priority date: 2019-08-08
Filing date: 2020-08-07
Publication date: 2022-06-15
Also published as: WO2021025170A1; JPWO2021025170A1; CN114008276A; CN114008276B; EP4012114A4

Abstract

An excavator which suitably utilizes hydraulic oil flowing out of a boom cylinder during excavation is provided. An excavator includes a boom; an arm; a boom cylinder configured to drive the boom; and an arm cylinder configured to drive the arm. During excavation, the excavator increases a pressure at a rod side with respect to the boom cylinder and supplies the pressure to the arm cylinder.

Description

[Technical Field]

The present invention relates to an excavator.

[Background Art]

For example, Patent Document 1 discloses an excavator in which hydraulic oil flowing out of a bottom-side oil chamber of a boom cylinder is used by a regenerative oil-hydraulic motor when lowering the boom.

[Prior art document]

[Patent Document]

[Patent Document 1] International Publication No. 2013/0358153

[Summary of Invention]

[Problem to be Solved by Invention]

However, in the excavator disclosed in Patent Document 1, regeneration by hydraulic oil flowing out of the boom cylinder during excavation is not considered.
Accordingly, it is an object of the present invention to provide an excavator that suitably utilizes hydraulic oil flowing out of a boom cylinder during excavation.

[Means for Solving Problem]

An excavator according to one aspect of an embodiment includes a boom; an arm; a boom cylinder configured to drive the boom; and an arm cylinder configured to drive the arm. During excavation, the excavator increases a pressure at a rod side with respect to the boom cylinder and supplies the pressure to the arm cylinder.

[Advantageous Effects of Invention]

According to the present invention, it is possible to provide an excavator which suitably utilizes hydraulic oil flowing out of a boom cylinder during excavation.

[Brief Description of Drawings]

[Fig. 1] Fig. 1 is a side view of an excavator according to a first embodiment.
[Fig. 2] Fig. 2 is a view depicting a transition of an operation state of the excavator according to the first embodiment.
[Fig. 3] Fig. 3 is a diagram schematically depicting an example of a configuration in which a boom cylinder and an arm cylinder are oil-hydraulically driven in the excavator according to the first embodiment.
[Fig. 4] Fig. 4 is a flowchart depicting regenerative control with respect to oil during excavation in the excavator according to the first embodiment.
[Fig. 5] Fig. 5 is a diagram schematically depicting an example of a configuration in which a boom cylinder and an arm cylinder are oil-hydraulically driven in an excavator according to a second embodiment.

[Mode for Carrying out Invention]

Hereinafter, embodiments of the present invention will be described with reference to the drawings. In each drawing, descriptions are omitted for the same or corresponding configurations while the same or corresponding reference numerals are used.

«First embodiment»

First, an outline of an excavator 100 according to a first embodiment will be described with reference to Fig. 1. Fig. 1 is a side view of the excavator 100 according to the first embodiment.
The excavator 100 according to the first embodiment includes a lower traveling body 1; an upper swiveling body 3 that is mounted to the lower traveling body 1 in a swivelable manner through a swiveling mechanism 2; attachments (working devices) that include a boom 4, an arm 5, and a bucket 6; and a cabin 10.
In the lower traveling body 1, a pair of right and left crawlers are oil-hydraulically driven by traveling oil-hydraulic motors (not depicted) to cause the excavator 100 to travel. That is, the pair of traveling oil-hydraulic motors (examples of a traveling motor) drives the lower traveling body 1 (the crawlers) that is a driving target.
The upper swiveling body 3 is driven by a swiveling oil-hydraulic motor (not depicted) to rotate relative to the lower traveling body 1. That is, the swiveling oil-hydraulic motor is a swiveling driving unit which drives the upper swiveling body 3 that is a driving target, and is configured to change an orientation of the upper swiveling body 3.
The upper swiveling body 3 may be electrically driven by an electric motor (hereinafter, referred to as a "swiveling electric motor") instead of the swiveling oil-hydraulic motor. In other words, the swiveling electric motor is a swiveling driving unit that drives the upper swiveling body 3 that is a driving target, similar to the swiveling oil-hydraulic motor, and is configured to change an orientation of the upper swiveling body 3.
The boom 4 is mounted at a front and center portion of the upper swiveling body 3 tiltably in a vertical direction; the arm 5 is mounted to an extending end of the boom 4 rotatably in a vertical direction, and the bucket 6 as an end attachment is mounted to an extending end of the arm 5 rotatably in a vertical direction. The boom 4, the arm 5, and the bucket 6 are oil-hydraulically driven by boom cylinders 7, an arm cylinder 8, and a bucket cylinder 9, respectively, that are oil-hydraulic actuators.
The bucket 6 is an example of an end attachment. Another end attachment, such as a bucket for a slope, a dredging bucket, a breaker, or the like, may be attached to the end of the arm 5 instead of the bucket 6, depending on a specific work or the like.
The cabin 10 is a driving room for an operator, and is mounted at a front and left portion of the upper swiveling body 3.
Next, an excavation and loading operation that is an example of an operation of the excavator 100 according to the first embodiment will be described with reference to Fig. 2. Fig. 2 is a diagram depicting a transition of an operation state of the excavator 100 according to the first embodiment.
First, as indicated as a state CD1, the operator swivels the upper swiveling body 3; lowers the boom 4 in a state where the bucket 6 is above an excavation position, the arm 5 is opened, and the bucket 6 is opened; and lowers the bucket 6 so that a tip of the bucket 6 is at a desired height from an excavation target. Normally, when swiveling the upper swiveling body 3 and lowering the boom 4, the operator visually checks a position of the bucket 6. In addition, swiveling the upper swiveling body 3 and lowering the boom 4 are generally performed simultaneously. The above-described operations are referred to as boom-lowering and swiveling operations, and a corresponding section of operations is called a boom-lowering and swiveling operation section.
When the operator determines that the tip of the bucket 6 has reached a desired height, the operator closes the arm 5 until the arm 5 becomes substantially perpendicular to the ground surface, as indicated as a state CD2. Thus, soil at a desired depth is excavated and is scraped and collected with the bucket 6 until the arm 5 becomes substantially perpendicular to the ground surface. The operator then further closes the arm 5 and bucket 6, as indicated as a state CD3, and closes the bucket 6 until the bucket 6 becomes substantially perpendicular to the arm 5, as indicated as a state CD4. Thus, the bucket 6 is closed until an upper edge of the bucket 6 becomes substantially horizontal, and thus, collected soil is put in the bucket 6. The above described operations are referred to as excavation operations and a corresponding section of operations is referred to as an excavation operation section.
In this regard, during an operation from the state CD1 to the state CD2 in the excavation operations, for example, the arm 5 is operated in a closing direction, and thus, the arm 5 is operated in such a manner that a rod of the arm cylinder 8 is elongated. As a result, the arm 5 rotates about a pin that acts as a fulcrum and connects the boom 4 and the arm 5, and the bucket 6 excavates the ground. At this time, due to a reaction force from the ground, a force is applied to the pin that connects the boom 4 and the arm 5 in a direction of lifting the pin. For this reason, the boom cylinders 7 receive reaction forces in directions to elongate rods. In this regard, the operator performs an operation to slightly lift the boom at the same time of performing an operation to close the arm. as a result, an amount of hydraulic oil in accordance with an amount of the operation is supplied from a main pump 14A to bottom-side oil chambers of the boom cylinders 7.
Next, in response to the operator determining that the bucket 6 has been closed until becoming substantially perpendicular to the arm 5, the operator lifts the boom 4 until a bottom of the bucket 6 comes to be at a desired height from the ground, with the bucket 6 kept closed, as indicated as a state CD5. These operations are referred to as boom-lifting operations, and a corresponding section of operations is referred to as a boom-lifting operation section. Following or simultaneously with these operations, the operator swivels the upper swiveling body 3 and rotates and moves the bucket 6 to a soil discharging position, as indicated as an arrow AR1. These operations including a boom lifting operation are referred to as boom-lifting and swiveling operations, and a corresponding section of operations is referred to as a boom-lifting and swiveling operation section.
The reason why the boom 4 is thus lifted until the bottom of the bucket 6 reaches the desired height is that, for example, if the bucket 6 is not lifted higher than a height of a loading bed of a dump truck, the bucket 6 may hit the loading bed when discharging soil onto the loading bed.
Next, in response to the operator determining that the boom-lifting and swiveling operations have been completed, the operator opens the arm 5 and the bucket 6 while lowering or stopping the boom 4 as indicated as a state CD6 to discharge soil from the bucket 6. These operations are referred to as dumping operations and a corresponding section of operations is referred to as a dumping operation section.
Next, in response to the operator determining that the dumping operations have been completed, the operator swivels the upper swiveling body 3 in a direction of an arrow AR2 as indicated as a state CD7, and moves the bucket 6 to precisely above the excavation position. At this time, the operator lowers the boom 4 at the same time of swiveling, and lowers the bucket 6 to a desired height from an excavating target. These operations are part of the boom-lowering and swiveling operations described above with respect to the state CD1. Thereafter, the operator moves the bucket 6 down to a desired height as indicated as a state CD1 to perform again operations starting from excavation operations.
The operator repeats a cycle of the above-described "boom-lowering swiveling operations", "excavation operations", "boom-lifting and swiveling operations", and "dumping operations" to proceed with the excavating and dumping work.
Fig. 3 is a diagram schematically depicting an example of a configuration in which the boom cylinders 7 and the arm cylinder 8 are oil-hydraulically driven in the excavator 100 according to the first embodiment. In Fig. 3, control valves 175B, 175R, 176B, and 176R, and a regenerative valve 19 are depicted in states at a time of regeneration, which will be described later. In Fig. 3 (and Fig. 5 to be described later), mechanical power lines are depicted by double lines, and hydraulic oil lines are depicted by solid lines. Directions of movement of rods during regeneration that will be described later are indicated by blank arrows and flows of hydraulic oil during regeneration are indicated by black arrows.
Driving systems of the excavator 100 according to the first embodiment include an engine 11, regulators 13A and 13B, main pumps 14A and 14B, and control valves 17. Oil-hydraulic driving systems of the excavator 100 according to the first embodiment include oil-hydraulic actuators such as the traveling oil-hydraulic motor (not depicted), the swiveling oil-hydraulic motor (not depicted), the boom cylinders 7, the arm cylinder 8, and the bucket cylinder 9, oil-hydraulically driving the lower traveling body 1, the upper swiveling body 3, the boom 4, the arm 5, and the bucket 6, respectively, as described above. In Fig. 3, the oil-hydraulic driving systems of the boom cylinders 7 and the arm cylinder 8 are depicted, but the oil-hydraulic driving systems of the other oil-hydraulic actuators (such as the traveling oil-hydraulic motor (not depicted), the swiveling oil-hydraulic motor (not depicted), the bucket cylinder 9, and so forth) are omitted.
The engine 11 is a main power source with respect to the oil-hydraulic driving systems and is mounted, for example, at a rear portion of the upper swiveling body 3. Specifically, the engine 11, under direct or indirect control of a controller 30, rotates at a predetermined target speed and drives the main pumps 14A and 14B. The engine 11 is, for example, a diesel engine fueled with light oil.
The regulator 13A controls a discharge amount of the main pump 14A. For example, the regulator 13A adjusts an angle (tilt angle) of a swash plate of the main pump 14A in accordance with a control command from the controller 30. Similarly, the regulator 13B controls a discharge rate of the main pump 14B.
The main pumps 14A and 14B are mounted, for example, at a rear portion of the upper swiveling body 3, where also the engine 11 is mounted, to supply hydraulic oil to the control valves 17 through high pressure hydraulic oil lines. The main pumps 14A and 14B are driven by the engine 11 as described above. The main pumps 14A and 14B are, for example, variable displacement oil-hydraulic pumps; and, as described above, under the control of the controller 30, stroke lengths of pistons are adjusted by adjusting the tilt angles of the swash plates by the regulators 13A and 13B, and thus, the discharge flow rates (discharge pressures) are controlled.
The control valves 17 are mounted, for example, at a center portion of the upper swiveling body 3 and are oil-hydraulic control devices that control the oil-hydraulic driving systems in accordance with operations performed by an operator on a manual operating device (not depicted). As described above, the control valves 17 are connected to the main pumps 14A and 14B via high pressure hydraulic oil lines and selectively supply hydraulic oil supplied from the main pumps 14A and 14B to oil-hydraulic actuators (the traveling oil-hydraulic motor, swiveling oil-hydraulic motor, boom cylinders 7, arm cylinder 8, and bucket cylinder 9), in accordance with operated states with respect to the manual operating device (not depicted).
Specifically, the control valves 17 include the control valves 175B, 175R, 176B, and 176R for controlling flow rates and directions of hydraulic oil supplied from the main pumps 14A and 14B to the boom cylinders 7 and the arm cylinder 8, respectively. The control valves 175B and 175R correspond to the boom cylinders 7, and the control valves 176B and 176R correspond to the arm cylinder 8.
The control valves 175B, 175R, 176B, and 176R may be, for example, solenoid spool valves driven by commands from the controller 30. The control valves 175B, 175R, 176B, and 176R have pump-side ports, tank-side ports, and actuator-side ports.
The pump-side port of the control valve 175B is connected to the main pump 14A through a hydraulic oil passage C1. The tank-side port of the control valve 175B is connected to a hydraulic oil tank through a hydraulic oil passage C7. The actuator-side port of the control valve 175B is connected to bottom-side oil chambers of the boom cylinders 7 through a hydraulic oil passage C2.
The pump-side port of the control valve 175R is connected to the main pump 14A through the hydraulic oil passage C1. The tank-side port of the control valve 175R is connected to the hydraulic oil tank through the hydraulic oil passage C7. The actuator-side port of the control valve 175R is connected to rod-side oil chambers of the boom cylinders 7 through a hydraulic oil passage C3.
The pump-side port of the control valve 176B is connected to the main pump 14B through a hydraulic oil passage C4. The tank-side port of the control valve 176B is connected to the hydraulic oil tank through the hydraulic oil passage C7. The actuator-side port of the control valve 176B is connected to a bottom-side oil chamber of the arm cylinder 8 through a hydraulic oil passage C5.
The pump-side port of the control valve 176R is connected to the main pump 14B through the hydraulic oil passage C4. The tank-side port of the control valve 176R is connected to the hydraulic oil tank through the hydraulic oil passage C7. The actuator-side port of the control valve 176R is connected to the rod-side oil chamber of the arm cylinder 8 through a hydraulic oil passage C6.
The hydraulic oil passage C1 is connected at one end to the main pump 14A and at the other branch ends to the pump-side port of the control valve 175B and to the pump-side port of the control valve 175R. The hydraulic oil passage C2 is connected at one end to the actuator-side port of the control valve 175B and at the other branch ends to the bottom-side oil chambers of the boom cylinders 7. The hydraulic oil passage C3 is connected at one end to the actuator-side port of the control valve 175R and at the other branch ends connected to the rod-side oil chambers of the boom cylinders 7. The hydraulic oil passage C4 is connected at one end to the main pump 14B and at the other branch ends to the pump-side port of the control valve 176B and to the pump-side port of the control valve 176R. The hydraulic oil passage C5 is connected at one end to the actuator-side port of the control valve 176B and at the other end to the bottom-side oil chamber of the arm cylinder 8. The hydraulic oil passage C6 is connected at one end to the actuator-side port of the control valve 176R and at the other end to the rod-side oil chamber of the arm cylinder 8. The hydraulic oil passage C7 is connected at one end to the hydraulic oil tank and at the other branch ends to the tank-side ports of the control valves 175B, 175R, 176B, and 176R.
The excavator 100 according to the first embodiment includes a regenerator 41 that regenerates pressures of the rod-side oil chambers of the boom cylinders 7A and 7B at the bottom-side oil chamber of the arm cylinder 8. The regenerator 41 includes hydraulic oil passages C8 and C9, a pressure intensifier mechanism 18, and a regenerative valve 19.
The hydraulic oil passage C8 is connected at one end to the hydraulic oil passage C3 (i.e., to the rod-side oil chambers of the boom cylinders 7) and at the other end to a primary chamber of the pressure intensifier mechanism 18. The hydraulic oil passage C9 is connected at one end to a secondary chamber of the pressure intensifier mechanism 18 and at the other end to the hydraulic oil passage C5 (i.e., to the bottom-side oil chamber of the arm cylinder 8).
The pressure intensifier mechanism 18 is a device that increases a pressure at an input side and outputs the pressure from an output side. For example, a pressure intensifier piston may be used. The pressure intensifier piston includes a primary chamber at an input side, a secondary chamber at an output side, and a piston that separates the primary chamber and the secondary chamber. A pressure at the input side is increased in accordance with a pressure receiving area ratio, and the pressure is output from the output side. A configuration of the pressure intensifier mechanism 18 is not limited thereto, and may be a rotary pressure intensifier mechanism.
The regenerative valve 19 is provided in the hydraulic oil passage C9 and is an open/close valve for opening and closing the hydraulic oil passage C9. The regenerative valve 19 may be, for example, a solenoid valve which is driven by a command from the controller 30.
Boom rod pressure sensors S7R detect oil pressures at the rod-side oil chambers of the boom cylinders 7. Boom bottom pressure sensors S7B detect oil pressures at the bottom-side oil chambers of the boom cylinders 7. An arm rod pressure sensor S8R detects an oil pressure at the rod-side oil chamber of the arm cylinder 8. An arm bottom pressure sensor S8B detects an oil pressure at the bottom-side oil chamber of the arm cylinder 8.
Operations of the oil-hydraulic driving systems under normal conditions will now be described. Normally, the regenerative valve 19 is closed. When the boom 4 is to be lifted or lowered, the controller 30 lifts or lowers the boom 4 by elongating or shortening the boom cylinders 7 by controlling the control valves 175B and 175R in response to an operation signal (i.e., the operator's lever operation) to operate the boom 4. When the arm 5 is to be closed or opened, the controller 30 opens or closes the arm 5 by elongating or shortening the arm cylinder 8 by controlling the control valves 176B and 176R in response to an operation signal (i.e., the operator's lever operation) to operate the arm 5.

Fig. 4 is a flowchart depicting regenerative control with respect to oil in excavation operations of the excavator 100 according to the first embodiment.
It is assumed that the operator performs an operation to close the arm 5. Thus, the controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). Hydraulic oil discharged from the main pump 14B is supplied to the bottom-side oil chamber of the arm cylinder 8 through the hydraulic oil passage C4, the control valve 176B, and the hydraulic oil passage C5. Hydraulic oil flowing out of the rod-side oil chamber of the arm cylinder 8 flows into the hydraulic oil tank through the hydraulic oil passage C6, the control valve 176R, and the hydraulic oil passage C7. At the same time of thus performing the operation to close the arm 5, the operator performs an operation to slightly lift the boom 4. Thus, the controller 30 opens the control valves 175B and 175R in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). Hydraulic oil discharged from the main pump 14A is supplied to the bottom-side oil chambers of the boom cylinders 7A and 7B through the hydraulic oil passage C1, the control valve 175B, and the hydraulic oil passage C2. Hydraulic oil flowing out of the rod-side oil chambers of the boom cylinders 7A and 7B flows into the hydraulic oil tank through the hydraulic oil passage C3, the control valve 175R, and the hydraulic oil passage C7.
In step S1, the controller 30 determines whether excavation has been started. For example, the controller 30 determines whether excavation has started, for example, by determining whether the bucket 6 has detected a reaction force generated when excavating the ground. For example, the controller 30 determines whether excavation has started based on a difference between a detected pressure of the boom rod pressure sensor S7R, which detects an oil pressure at the rod-side oil chambers of the boom cylinders 7 and a detected pressure of the arm bottom pressure sensor S8B, which detects an oil pressure at the bottom-side oil chamber of the arm cylinder 8. Instead, the controller 30 may determine whether excavation has started, for example, based on an image taken by a forward view camera 60F. When having determined that excavation has not been started (S1: No), the controller 30 repeats step S1. When having determined that excavation has been started (S1: Yes), the controller 30 proceeds to step S2.
In step S2, the controller 30 determines whether a differential pressure ΔP is greater than or equal to a threshold Pref1. In this regard, C denotes a pressure intensifying factor of the pressure intensifier mechanism 18, Pbr denotes oil pressures at the rod-side oil chambers of the boom cylinders 7, Pab denotes an oil pressure at the bottom-side oil chamber of the arm cylinder 8, and the differential pressure ΔP is obtained from the following formula (1). The threshold Pref1 has a predetermined threshold (offset value), and, for example, "Pref1 = 0" holds. $Δ P = CPbr - Pab$
When the differential pressure ΔP is smaller than the threshold Pref1 (S2: No), the controller 30 repeats step S2. When the differential pressure ΔP is greater than or equal to the threshold Pref1 (S2: Yes), the controller 30 proceeds to step S3.
In step S3, the controller 30 opens the regenerative valve 19. In addition, the controller 30 closes the control valve 175R. The controller 30 opens the control valve 175B in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). In addition, the controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). Hydraulic oil flowing out of the rod-side oil chambers of the boom cylinders 7A and 7B flows to the input side of the pressure intensifier mechanism 18 through the hydraulic oil passage C8. As a result, oil pressures at the rod-side oil chambers of the boom cylinders 7 are increased by the pressure intensifier mechanism 18, and a resulting oil pressure is supplied to the bottom-side oil chamber of the arm cylinder 8.
In step S4, the controller 30 determines whether the differential pressure ΔP is smaller than a threshold Pref2. The threshold Pref2 is a predetermined threshold (offset value), for example, "Pref2 = 0" holds. The thresholds Pref1 and Pref2 may be the same as or different from each other. In order to prevent hunting of control, "Pref1 > Pref2" is preferable. When the differential pressure ΔP is not smaller than the threshold Pref2 (S4: No), the controller 30 repeats step S4. When the differential pressure ΔP is smaller than the threshold Pref2 (S4: Yes), the controller 30 proceeds to step S5.
In step S5, the controller 30 closes the regenerative valve 19. The controller 30 opens the control valves 175B and 175R in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). The controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). As a result, regenerative oil pressure supply from the rod-side oil chambers of the boom cylinders 7 to the bottom-side oil chamber of the arm cylinder 8 ends. Then, the controller 30 ends the process depicted in Fig. 3.
As described above, according to the excavator 100 of the first embodiment, reaction forces generated at the boom cylinders 7 during excavation can be effectively utilized by the arm cylinder 8 that drives the arm 5 to perform excavation. Therefore, it is possible to improve an operating speed and reduce energy consumption of the excavator 100 during excavation.
Further, according to the excavator 100 of the first embodiment, even when, for example, the reaction forces are small and pressures at the rod-side oil chambers of the boom cylinders 7 are smaller than a pressure at the bottom-side oil chamber of the arm cylinder 8, pressures (reaction forces) generated at the boom cylinders 7 can be utilized by the arm cylinder 8 that is driven during excavation operations, by increasing a pressure by the pressure intensifier mechanism 18.

«Second embodiment»

Next, the excavator 100 according to a second embodiment will be described. Fig. 5 is a diagram schematically depicting an example of a configuration in which the boom cylinders 7 and the arm cylinder 8 are oil-hydraulically driven in the excavator 100 according to the second embodiment. In Fig. 5, the control valves 175B, 175R, 176B, and 176R and regenerative valves 20 and 21 are in states at the time of regeneration that will be described later.
The excavator 100 according to the second embodiment differs from the excavator 100 according to the first embodiment in that the excavator 100 according to the second embodiment has the regenerator 41 depicted in Fig. 3, while the excavator 100 according to the second embodiment has a regenerator 42 depicted in Fig. 5. Other configurations are the same and duplicate descriptions are omitted.
The hydraulic oil passage C3 includes a hydraulic oil passage C11, a hydraulic oil passage C12, and the regenerative valve 20. The hydraulic oil passage C11 is connected at one end to the rod-side oil chamber of the boom cylinder 7A and at the other end to one port of the regenerative valve 20. The hydraulic oil passage C12 is connected at one end to an actuator-side port of the control valve 175R and at the other branch ends to the other port of the regenerative valve 20 and the rod-side oil chamber of the boom cylinder 7B.
The regenerative valve 20 is provided at a connection between the hydraulic oil passage C11 and the hydraulic oil passage C12, and is an open/close valve to enable and disable communicating between the hydraulic oil passage C11 and the hydraulic oil passage C12. The regenerative valve 20 may be, for example, a solenoid valve that is driven by a command from the controller 30.
The excavator 100 according to the second embodiment includes the regenerator 42 that regenerates a pressure of the rod-side oil chamber of the boom cylinder 7A at the bottom-side oil chamber of the arm cylinder 8. The regenerator 42 includes a hydraulic oil passage C13 and the regenerative valves 20 and 21.
The hydraulic oil passage C13 is connected at one end to the hydraulic oil passage C11 (i.e., to the rod-side oil chambers of the boom cylinders 7A) and at the other end to the hydraulic oil passage C5 (i.e., the bottom-side oil chamber of the arm cylinder 8).
The regenerative valve 21 is provided in the hydraulic oil passage C13 and is an open/close valve for opening and closing the hydraulic oil passage C13. The regenerative valve 19 may be, for example, a solenoid valve which is driven by a command from the controller 30.
Operations of the oil-hydraulic driving systems under normal conditions will now be described. Normally, the regenerative valve 20 is opened and the regenerative valve 21 is closed. When the boom 4 is to be lifted or lowered, the controller 30 elongates or shortens the boom cylinders 7 by controlling the control valves 175B and 175R in response to an operation signal (i.e., the operator's lever operation) to operate the boom 4, resulting in lifting or lowering the boom 4. When the arm 5 is to be closed or opened, the controller 30 elongates and shortens the arm cylinder 8 by controlling the control valves 176B and 176R in response to an operation signal (i.e., the operator's lever operation) to operate the arm 5, resulting in closing or opening the arm 5.

The excavator 100 according to the second embodiment differs in the following points with respect to the flowchart depicted in Fig. 4.
It is assumed that the operator performs an operation to close the arm 5. Thus, the controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). Hydraulic oil discharged from the main pump 14B is supplied to the bottom-side oil chamber of the arm cylinder 8 through the hydraulic oil passage C4, the control valve 176B, and the hydraulic oil passage C5. Hydraulic oil flowing out of the rod-side oil chamber of the arm cylinder 8 flows into the hydraulic oil tank through the hydraulic oil passage C6, the control valve 176R, and the hydraulic oil passage C7. At the same time of performing the operation to close the arm 5, the operator performs an operation to slightly lift the boom 4. Thus, the controller 30 opens the control valves 175B and 175R in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). Hydraulic oil discharged from the main pump 14A is supplied to the bottom-side oil chambers of the boom cylinders 7A and 7B through the hydraulic oil passage C1, the control valve 175B, and the hydraulic oil passage C2. Hydraulic oil flowing out of the rod-side oil chambers of the boom cylinders 7A and 7B flows into the hydraulic oil tank through the hydraulic oil passage C3, the control valve 175R, and the hydraulic oil passage C7.
In step S3, the controller 30 opens the regenerative valve 21 and closes the regenerative valve 20. In addition, the controller 30 opens the control valve 175R so that the hydraulic oil passage C3 (C12) communicates with the hydraulic oil passage C7. The controller 30 opens the control valve 175B in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). In addition, the controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). Hydraulic oil flowing out of the rod-side oil chamber of the boom cylinder 7B flows into the hydraulic oil tank through the hydraulic oil passage C12, the control valve 175R, and the hydraulic oil passage C7. Hydraulic oil flowing out of the rod-side oil chamber of the boom cylinder 7A is supplied to the bottom-side oil chamber of the arm cylinder 8 through the hydraulic oil passage C13.
In step S5, the controller 30 opens the regenerative valve 21 and opens the regenerative valve 20. In addition, the controller 30 opens the control valves 175B and 175R in response to an operation signal (e.g., the operator's lever operation to operate the boom 4). In addition, the controller 30 opens the control valves 176B and 176R in response to an operation signal (e.g., the operator's lever operation to operate the arm 5). As a result, regenerative oil pressure supply from the rod-side oil chamber of the boom cylinder 7A to the bottom-side oil chamber of the arm cylinder 8 ends.
Other processes are the same and duplicate descriptions are omitted.
As described above, according to the excavator 100 of the second embodiment, reaction forces generated at the boom cylinders 7 during excavation can be effectively utilized by the arm cylinder 8 that drives the arm 5 to perform excavation. Therefore, it is possible to improve the operating speed and reduce the energy consumption of the excavator 100 during excavation.
Further, according to the excavator 100 of the second embodiment, the one boom cylinder 7A from among the two boom cylinders 7 (7A and 7B) receives a reaction force. Therefore, as a result of the reaction force being received by the one boom cylinder 7A during excavation, a pressure increase at the rod-side oil chamber of the boom cylinder 7A due to a reaction force is greater compared to a case where the reaction force during excavation is received by the two boom cylinders 7. Therefore, even if the reaction force is small, a pressure at the rod-side oil chamber of the boom cylinder 7A can be made to be higher than a pressure at the bottom-side oil chamber of the arm cylinder 8. Therefore, a pressure (reaction force) generated at the boom cylinders 7 can be utilized by the arm cylinder 8 which is driven during excavation operations.
Although the embodiments of the excavator 100 and so forth have been described above, the present invention is not limited to the above-described embodiments and so forth, and various modifications and improvements can be made within the scope of the present invention described in the appended claims.
The present application claims priority based on Japanese Patent Application No. 2019-146180, filed August 8, 2019 , the entire contents of which are hereby incorporated by reference.

[Description of Symbols]

1 Lower traveling body
2 Swiveling mechanism
3 Upper swiveling body
4 Boom
5 Arm
6 Bucket
7 Boom cylinder
8 Arm cylinder
9 Bucket cylinder
10 Cabin
11 Engine
14A and 14B Main pumps
17 Control valves
175B, 175R, 176B, 176R Control valves
18 Pressure intensifier mechanism
19, 20, 21 Regenerative valves
30 Controller
41, 42 Regenerators
100 Excavator

Claims

An excavator comprising:
a boom;

an arm;

a boom cylinder configured to drive the boom; and

an arm cylinder configured to drive the arm,

wherein

during excavation, the excavator increases a pressure at a rod side with respect to the boom cylinder and supplies the pressure to the arm cylinder.
The excavator as claimed in claim 1,
wherein hydraulic oil that is increased in pressure and is supplied to the arm cylinder is increased in pressure by a pressure intensifier mechanism configured to increase hydraulic oil flowing out of the rod side with respect to the boom cylinder.
The excavator as claimed in claim 1,
wherein
the boom cylinder configured to drive the boom includes two boom cylinders, and

hydraulic oil that is increased in pressure and is supplied to the arm cylinder is increased in pressure as a result of hydraulic oil flowing out of a rod side with respect to one of the two boom cylinders being supplied to the arm cylinder.
The excavator as claimed in claim 1, comprising:
a regenerative hydraulic oil passage connecting a rod side with respect to the boom cylinder and a bottom side with respect to the arm cylinder;

a pressure intensifier mechanism provided in the regenerative hydraulic oil passage; and

an opening/closing valve configured to open and close the regenerative hydraulic oil passage.
The excavator as claimed in claim 1,
wherein
the boom cylinder configured to drive the boom includes a first boom cylinder and a second boom cylinder, and

the excavator includes:
a regenerative hydraulic oil passage connecting a rod side with respect to the first boom cylinder and a bottom side with respect to the arm cylinder,

a regenerative opening/closing valve configured to open and close the regenerative hydraulic oil passage, and

a main opening/closing valve provided in a main hydraulic oil passage that connects the rod side with respect to the first boom cylinder and a control valve, and configured to open and close the main hydraulic oil passage.