Working machine and method for controlling working machine

Abstract

To achieve the same level of operability with horizontal control and up-tilt operation.SOLUTION: A work machine comprises a first oil passage connecting a first hydraulic pump and a first chamber of a bucket cylinder, a fourth oil passage connecting an arm control valve and a fourth chamber of the bucket cylinder, an arm operation detection sensor that detects the operation of an arm input member, a bucket operation detection sensor that detects the operation of a bucket input member, a bypass oil passage configured to connect the fourth oil passage and the first oil passage, a switching mechanism configured to control connection and disconnection between the fourth oil passage and the first oil passage by the bypass oil passage, and a control device. The control device is configured to determine whether an up-tilt operation is performed to raise the arm and tilt the bucket downward based on the output of the arm operation detection sensor and the output of the bucket operation detection sensor, and control the switching mechanism to connect the fourth oil passage and the first oil passage when it is determined that the up-tilt operation has been performed.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a work machine and a method for controlling the work machine. [Background technology]

[0002] Patent Document 1 discloses a work machine including a hydraulic system for performing horizontal control to prevent a load from falling by changing the tilt angle of a bucket in accordance with the lifting of an arm when the arm is lifted. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6919479 Summary of the Invention [Problem to be solved by the invention]

[0004] In the work machine described in Patent Document 1, in the uptilt operation in which the bucket is tilted downward while the arm is raised, the hydraulic control of the arm and the hydraulic control of the bucket are not linked as in horizontal control, and the hydraulic control for raising the arm and the hydraulic control for tilting the bucket are performed separately, resulting in a problem in that the tilt speed of the uptilt operation when the horizontal control is enabled differs from that of the uptilt operation when the horizontal control is disabled.

[0005] An object of the technology disclosed in the present application is to provide a work machine and a control method for the work machine that are capable of achieving the same level of operability with uptilt operation regardless of whether horizontal control is enabled or not. [Means for solving the problem]

[0006] A working machine according to a first aspect of the present disclosure includes a bucket, an arm, a vehicle body, a bucket cylinder, an arm cylinder, a first hydraulic pump, a first oil passage, a bucket control valve, a second oil passage, a third oil passage, an arm control valve, a fourth oil passage, a second hydraulic pump, a first pilot oil passage, an arm pilot control valve, an arm operation detection sensor, a second pilot oil passage, a bucket pilot control valve, a bucket operation detection sensor, a bypass oil passage, a switching mechanism, and a control device. The bucket includes a bucket base end and a bucket tip end opposite the bucket base end. The arm includes an arm tip end that swingably supports the bucket base end and an arm base end opposite the arm tip end. The vehicle body swingably supports the arm base end. The bucket cylinder includes a first chamber into which hydraulic oil flows when the bucket tip end is tilted downward and a second chamber into which hydraulic oil flows when the bucket tip end is tilted upward. The arm cylinder includes a third chamber into which hydraulic oil flows when the arm tip is raised and a fourth chamber into which hydraulic oil flows when the arm tip is lowered. The first hydraulic pump is configured to discharge hydraulic oil to the bucket cylinder and the arm cylinder. The first oil passage connects the first hydraulic pump to the first chamber of the bucket cylinder. The bucket control valve is provided in the first oil passage and has a bucket control pilot port. The bucket control valve is configured to control the hydraulic oil supplied to the first chamber and the second chamber according to the hydraulic pressure of the pilot oil applied to the bucket control pilot port. The second oil passage connects the bucket control valve to the second chamber. The third oil passage connects the first hydraulic pump to the third chamber of the arm cylinder. The arm control valve is provided in the third oil passage and has an arm control pilot port. The arm control valve is configured to control the hydraulic oil supplied to the third chamber and the fourth chamber according to the hydraulic pressure of the pilot oil applied to the arm control pilot port. The fourth oil passage connects the arm control valve to the fourth chamber. The second hydraulic pump is configured to discharge pilot oil for controlling the arm control valve and the bucket control valve. The first pilot oil passage connects the arm control pilot port and the second hydraulic pump.The arm pilot control valve is provided in the first pilot oil passage, and controls the hydraulic pressure of the pilot oil applied to the arm control pilot port based on the operation amount of the arm input member operated to raise and lower the arm. The arm operation detection sensor detects the operation of the arm input member. The second pilot oil passage connects the bucket control pilot port and the second hydraulic pump. The bucket pilot control valve is provided in the second pilot oil passage, and controls the hydraulic pressure of the pilot oil applied to the bucket control pilot port based on the operation amount of the bucket input member operated to swing the bucket. The bucket operation detection sensor detects the operation of the bucket input member. The bypass oil passage is configured to connect the fourth oil passage and the first oil passage. The switching mechanism is configured to control the connection and disconnection of the fourth oil passage and the first oil passage by the bypass oil passage. The control device is configured to determine whether or not an uptilt operation that raises the arm and tilts the bucket downward has been performed based on the output of the arm operation detection sensor and the output of the bucket operation detection sensor, and to control the switching mechanism to connect the fourth oil passage and the first oil passage when it is determined that an uptilt operation has been performed.

[0007] A control method for a work machine according to a second aspect of the present disclosure tilts a bucket tip of a bucket downward by sending hydraulic oil from a first hydraulic pump through a first oil passage to a first chamber of a bucket cylinder. The control method communicates a first oil passage from the first hydraulic pump to the bucket control valve with a second oil passage connecting the bucket control valve and a second chamber of the bucket cylinder by a bucket control valve provided in the first oil passage, and sends hydraulic oil from the first hydraulic pump to the second chamber of the bucket cylinder to tilt the bucket tip upward. The control method sends hydraulic oil from the first hydraulic pump through a third oil passage to a third chamber of an arm cylinder to raise an arm tip of an arm that swingably supports a bucket base end opposite to the bucket tip of the bucket. In this control method, an arm control valve provided in a third oil passage communicates a third oil passage from a first hydraulic pump to the arm control valve with a fourth oil passage connecting the arm control valve and a fourth chamber of the arm cylinder, and hydraulic oil from the first hydraulic pump is sent to the fourth chamber of the arm cylinder to lower the arm tip. In this control method, a first operation for lifting the arm is input to an arm input member operated to lift and lower the arm. In this control method, a second operation for tilting the bucket downward is input to a bucket input member operated to swing the bucket. In this control method, when the first and second operations are detected, hydraulic oil is sent to the first chamber via the first oil passage, and the fourth oil passage and the first oil passage are connected by a switching mechanism to send hydraulic oil in the fourth chamber to the first chamber. Effect of the Invention

[0008] According to the technology disclosed in the present application, for example, it is possible to provide a work machine and a control method for the work machine that are capable of achieving the same level of operability in horizontal control and uptilt operation. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a side view of the working machine. [Diagram 2] FIG. 2 is a top view of the work machine. [Diagram 3]FIG. 3 is a schematic diagram of a hydraulic system of a working machine. [Figure 4] FIG. 4 is a flowchart showing a method for controlling the work machine. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings, in which like reference numerals indicate corresponding or identical components in each drawing.

[0011] 1 and 2, a work machine 1, for example, a compact track loader, includes a vehicle body 2, a pair of travel devices 3, and a working device 4. The vehicle body 2 supports the travel devices 3 and the working device 4. In the illustrated embodiment, the travel devices 3 are track-type travel devices. Therefore, each of the pair of travel devices 3 includes a driving wheel 31, driven wheels 32 and 33, and rollers 34 driven by a hydraulic motor device 30. However, each of the pair of travel devices 3 is not limited to being a track-type travel device. Each of the pair of travel devices 3 may be, for example, a front-wheel / rear-wheel travel device, or a travel device having a front wheel and a rear crawler. The working device 4 includes a work equipment (bucket) 41 at the distal end of the working device 4. The bucket 41 includes a bucket base end 41P and a bucket tip end 41D opposite to the bucket base end 41P. A proximal end of the working device 4 is attached to the rear of the vehicle body 2. The working device 4 includes a pair of arm assemblies 42 for rotatably supporting the bucket 41 via a bucket pivot shaft 43. Each of the pair of arm assemblies 42 includes a link 44 and an arm 45. The arm 45 includes an arm tip portion 45D that swingably supports the bucket base end portion 41P, and an arm base end portion 45P opposite the arm tip portion 45D. The arm tip portion 45D swingably supports the bucket pivot shaft 43. The vehicle body 2 swingably supports the arm base end portion 45P. Specifically, the vehicle body 2 swingably supports the arm base end portion 45P via a link 44.

[0012] The link 44 is rotatable relative to the vehicle body 2 around a fulcrum shaft 46. The arm 45 is rotatable relative to the link 44 around a joint shaft 47. The working device 4 further includes a plurality of arm cylinders 48 and at least one bucket cylinder 49. Each of the plurality of arm cylinders 48 is rotatably connected to the vehicle body 2 and the arm 45, and moves the link 44 and the arm 45, etc., to lift and lower the bucket 41. The at least one bucket cylinder 49 is configured to tilt the bucket 41. The vehicle body 2 includes a cabin 5. The cabin 5 includes a front window 51 that can be opened and closed, and its outer shape is defined by a cab frame 53. The front window 51 may be omitted. The working machine 1 includes a driver's seat 54 and an operation lever 55 in the cabin 5. The cab frame 53 is rotatable around rotational shafts RSL and RSR on the vehicle body 2, as shown in FIG. 2. In FIG. 1 and FIG. 2, a common pivot axis A defined by the rotation axes RSL and RSR is XC That is, the cab frame 53 is rotatable about a rotation axis A XC It is mounted so as to be rotatable around

[0013] In the embodiment of the present application, FB (Forward direction D F / backward D B ) means the front-rear direction (front direction / rear direction) as seen from the operator seated in the driver's seat 54 of the cabin 5. L , right direction D R , width direction D W The left, right, left and right directions are respectively seen from the operator's point of view. U , downward D D , height direction D H The directions refer to the upward, downward, and height directions as seen by the operator. The forward / backward, left / right (width), and up / down (height) directions of the work machine 1 respectively correspond to the forward / backward, left / right (width), and up / down (height) directions as seen by the operator.

[0014] FIG. 1 shows the left side of the work machine 1. As shown in FIG. 2, the vehicle body 2 is generally symmetrical with respect to the vehicle body central plane M, and includes a first side surface 2L which is a left side surface, and a second side surface 2R which is a right side surface. Of the pair of traveling devices 3, the traveling device 3 provided on the first side surface 2L is shown as the first traveling device 3L, and the traveling device 3 provided on the second side surface 2R is shown as the second traveling device 3R. Of the pair of arm assemblies 42, the arm assembly 42 provided on the left side with respect to the vehicle body central plane M is shown as the first arm assembly 42L, and the arm assembly 42 provided on the right side with respect to the vehicle body central plane M is shown as the second arm assembly 42R. The link 44 provided on the left side with respect to the vehicle body central plane M is shown as the first link 44L. The arm 45 provided on the left side with respect to the vehicle body central plane M is shown as the first arm 45L, and the arm 45 provided on the right side with respect to the vehicle body central plane M is shown as the second arm 45R. The fulcrum shaft 46 provided on the left side with respect to the vehicle body central plane M is shown as the first fulcrum shaft 46L, and the fulcrum shaft 46 provided on the right side with respect to the vehicle body central plane M is shown as the second fulcrum shaft 46R. The joint shaft 47 provided on the left side with respect to the vehicle body central plane M is shown as the first joint shaft 47L, and the joint shaft 47 provided on the right side with respect to the vehicle body central plane M is shown as the second joint shaft 47R. Of the hydraulic motor units 30, the hydraulic motor unit 30 provided on the left side with respect to the vehicle body central plane M is shown as the first hydraulic motor unit 30L, and the hydraulic motor unit 30 provided on the right side with respect to the vehicle body central plane M is shown as the second hydraulic motor unit 30R.

[0015] 1 and 2, the work machine 1 further includes an engine 6 provided at the rear of the vehicle body 2, and a plurality of hydraulic pumps 7 including a first traveling hydraulic pump 7L and a second traveling hydraulic pump 7R. The engine 6 drives the plurality of hydraulic pumps 7. The first traveling hydraulic pump 7L and the second traveling hydraulic pump 7R are configured to discharge hydraulic oil to drive hydraulic actuators (such as a hydraulic motor device 30 that drives the drive wheels 31). The plurality of hydraulic pumps 7 other than the first traveling hydraulic pump 7L and the second traveling hydraulic pump 7R are configured to discharge hydraulic oil to drive hydraulic actuators (such as a plurality of arm cylinders 48 and at least one bucket cylinder 49) connected to the work device 4. The engine 6 is driven in a direction parallel to the width D of the work machine 1. W , and is provided between the pair of arm assemblies 42. The work machine 1 further includes a cover 8 for covering the engine 6. The work machine 1 further includes a bonnet cover 9 provided at the rear end of the vehicle body 2. The bonnet cover 9 can be opened and closed, allowing a maintenance technician to perform maintenance work on the engine 6, etc. <Hydraulic system>

[0016] The work machine 1 includes a hydraulic system 100. Fig. 3 is a schematic configuration diagram of the hydraulic system 100 of the work machine 1. The hydraulic system 100 includes the arm cylinder 48 and bucket cylinder 49 described above, the first hydraulic pump 11, the second hydraulic pump 12, the arm control valve 20, the bucket control valve 25, the arm pilot control valve 60, the bucket pilot control valve 65, the first oil passage R1, the second oil passage R2, the third oil passage R3, the fourth oil passage R4, the first pilot oil passage PR1, the second pilot oil passage PR2, a bypass oil passage BR1, a switching mechanism 70, arm operation detection sensors AS1 and AS2, bucket operation detection sensors BS1 and BS2, and a control device 15.

[0017] The bucket cylinder 49 includes a first chamber CB1 into which the hydraulic oil flows when the bucket tip 41D is tilted downward, and a second chamber CB2 into which the hydraulic oil flows when the bucket tip 41D is tilted upward. The arm cylinder 48 includes a third chamber CB3 into which the hydraulic oil flows when the arm tip 45D is raised, and a fourth chamber CB4 into which the hydraulic oil flows when the arm tip 45D is lowered. The first hydraulic pump 11 is driven by the engine 6 and configured to discharge hydraulic oil stored in the hydraulic oil tank 10 to the bucket cylinder 49 and the arm cylinder 48. The first hydraulic pump 11 is, for example, a variable displacement hydraulic pump. The second hydraulic pump 12 is driven by the engine 6 and configured to discharge pilot oil for controlling the arm control valve 20 and the bucket control valve 25. Of the hydraulic oil stored in the hydraulic oil tank 10, the hydraulic oil discharged from the second hydraulic pump 12 and used for control may be called pilot oil, and the pressure of the pilot oil may be called pilot pressure. The second hydraulic pump 12 is, for example, a fixed displacement hydraulic pump.

[0018] The first oil passage R1 connects the first hydraulic pump 11 and the first chamber CB1 of the bucket cylinder 49. The bucket control valve 25 is provided in the first oil passage R1, has bucket control pilot ports 25P1, 25P2, and is configured to control the hydraulic oil supplied to the first chamber CB1 and the second chamber CB2 of the bucket cylinder 49 in accordance with the hydraulic pressure of the pilot oil applied to the bucket control pilot ports 25P1, 25P2. The bucket control valve 25 is switched between a bucket cylinder stationary control position BNP, a bucket cylinder extension control position BEP, and a bucket cylinder retraction control position BSP in accordance with the pressure difference between the pilot pressure applied to the bucket control pilot port 25P1 and the pilot pressure applied to the bucket control pilot port 25P2. The first oil passage R1 includes a partial oil passage R10 that is common to the third oil passage R3 extending from the first hydraulic pump 11 to the joint J11, a partial oil passage R11 that extends from the joint J11 to the bucket control valve 25, a partial oil passage R12 that connects different connection ports of the bucket control valve 25, and a partial oil passage R13 that extends from the bucket control valve 25 to a first chamber CB1 of the bucket cylinder 49. The second oil passage R2 connects the bucket control valve 25 and a second chamber CB2 of the bucket cylinder 49. The first oil passage R1 and the second oil passage R2 are branched by being connected to different ports of the bucket control valve 25.

[0019] More specifically, bucket control valve 25 further includes a first bucket control valve port YP1, a second bucket control valve port YP2, and a third bucket control valve port YP3. The first bucket control valve port YP1 is connected to first hydraulic pump 11 via a first oil passage R1. The second bucket control valve port YP2 is connected to a first chamber CB1 of bucket cylinder 49 via the first oil passage R1. The third bucket control valve port YP3 is connected to a second oil passage R2. When the pilot pressure applied to bucket control pilot port 25P1 is greater than the pilot pressure applied to bucket control pilot port 25P2 by a predetermined pressure, bucket control valve 25 is switched to a bucket cylinder extension control position BEP that communicates between the first bucket control valve port YP1 and the second bucket control valve port YP2 and communicates between the third bucket control valve port YP3 and a first drain oil passage DR1 (described later). When the pilot pressure applied to bucket control pilot port 25P2 is greater than the pilot pressure applied to bucket control pilot port 25P1 by more than the predetermined pressure, bucket control valve 25 is switched to a bucket cylinder contraction control position BSP which communicates between the first bucket control valve port YP1 and the third bucket control valve port YP3 and communicates between the second bucket control valve port YP2 and DR1 (described later).When the absolute value of the difference between the pilot pressure applied to bucket control pilot port 25P2 and the pilot pressure applied to bucket control pilot port 25P1 is equal to or less than the predetermined pressure, bucket control valve 25 is switched to a bucket cylinder stationary control position BNP which isolates the first bucket control valve port YP1, the second bucket control valve port YP2, and the third bucket control valve port YP3. Note that hydraulic system 100 further includes a second pressure control valve 77 that connects the first bucket control valve port YP1 to the second bucket control valve port YP2 or the third bucket control valve port YP3 only when the pressure applied to the first bucket control valve port YP1 is equal to or higher than the fourth threshold pressure. This makes it possible to prevent bucket control from being performed unless the hydraulic pressure from first hydraulic pump 11 reaches the fourth threshold pressure.

[0020] The third oil passage R3 connects the first hydraulic pump 11 and the third chamber CB3 of the arm cylinder 48. The third oil passage R3 includes a partial oil passage R10 common to the first oil passage R1 extending from the first hydraulic pump 11 to the joint J11, and a partial oil passage R31 branching from the first oil passage R1 at the joint J11. The arm control valve 20 is provided in the third oil passage R3, has arm control pilot ports 20P1 and 20P2, and is configured to control the hydraulic oil supplied to the third chamber CB3 and the fourth chamber CB4 of the arm cylinder 48 according to the hydraulic pressure of the pilot oil applied to the arm control pilot ports 20P1 and 20P2. The arm control valve 20 is switched to an arm cylinder stationary control position ANP, an arm cylinder extension control position AEP, or an arm cylinder retraction control position ASP according to the pressure difference between the pilot pressure applied to the arm control pilot port 20P1 and the pilot pressure applied to the arm control pilot port 20P2. The third oil passage R3 further includes a partial oil passage R32 that connects different connection ports of the arm control valve 20, and a partial oil passage R33 that extends to the third chamber CB3 of the arm cylinder 48. The fourth oil passage R4 connects the arm control valve 20 and the fourth chamber CB4 of the arm cylinder 48. The third oil passage R3 and the fourth oil passage R4 are branched by being connected to different ports of the bucket control valve 25.

[0021] More specifically, the arm control valve 20 further includes a first arm control valve port XP1, a second arm control valve port XP2, and a third arm control valve port XP3. The first arm control valve port XP1 is connected to the first hydraulic pump 11 via a third oil passage R3. The second arm control valve port XP2 is connected to a fourth oil passage R4. The third arm control valve port XP3 is connected to a third chamber CB3 of the arm cylinder 48 via the third oil passage R3. When the pilot pressure applied to the arm control pilot port 20P1 is greater than the pilot pressure applied to the arm control pilot port 20P2 by a predetermined pressure, the arm control valve 20 is switched to an arm cylinder extended control position AEP that communicates the first arm control valve port XP1 with the third arm control valve port XP3 and communicates the second arm control valve port XP2 with a first drain oil passage DR1 (described later). When the pilot pressure applied to the arm control pilot port 20P2 is greater than the predetermined pressure than the pilot pressure applied to the arm control pilot port 20P1, the arm control valve 20 is switched to an arm cylinder contraction control position ASP which communicates the first arm control valve port XP1 with the second arm control valve port XP2 and communicates the third arm control valve port XP3 with the first drain oil passage DR1. When the absolute value of the difference between the pilot pressure applied to the arm control pilot port 20P2 and the pilot pressure applied to the arm control pilot port 20P1 is equal to or less than the predetermined pressure, the arm control valve 20 is switched to an arm cylinder stationary control position ANP which isolates the first arm control valve port XP1, the second arm control valve port XP2, and the third arm control valve port XP3. The hydraulic system 100 further includes a first pressure control valve 76 that communicates the first arm control valve port XP1 with the second arm control valve port XP2 or the third arm control valve port XP3 only when the pressure applied to the first arm control valve port XP1 is equal to or higher than a third threshold pressure. This makes it possible to prevent arm control from being performed unless the hydraulic pressure from the first hydraulic pump 11 reaches the third threshold pressure.

[0022] The first pilot oil passage PR1 connects the arm control pilot ports 20P1 and 20P2 to the second hydraulic pump 12. Specifically, the first pilot oil passage PR1 includes a partial oil passage PR10 common to the second pilot oil passage PR2 extending from the second hydraulic pump 12 to the joint J21, a partial oil passage PR11 extending from the joint J21 to the arm pilot control valve 60, a partial oil passage PR12 extending from the arm pilot control valve 60 to the arm control pilot port 20P1, and a partial oil passage PR13 extending from the arm pilot control valve 60 to the arm control pilot port 20P2. The hydraulic system 100 further includes an additional solenoid valve 14 provided in the partial oil passage PR10. That is, the additional solenoid valve 14 is provided in at least one of the first pilot oil passage PR1 between the second hydraulic pump 12 and the arm pilot control valve 60 and the second pilot oil passage PR2 between the second hydraulic pump 12 and the bucket pilot control valve 65. The additional solenoid valve 14 is a solenoid valve capable of changing the pressure of the hydraulic oil output from the second hydraulic pump 12. The pressure of this hydraulic oil can be changed under the control of the control device 15.

[0023] The arm pilot control valve 60 is provided in the first pilot oil passage PR1, and controls the hydraulic pressure of the pilot oil applied to the arm control pilot ports 20P1, 20P2 based on the operation amount of the arm input member 63 operated for raising and lowering the arm 45. Specifically, the arm pilot control valve 60 includes a pressure control valve 61 connected to the partial oil passage PR12 and a pressure control valve 62 connected to the partial oil passage PR12. When the arm input member 63 is tilted forward, the pressure control valve 61 is operated and pilot pressure is output from the pressure control valve 61 to the partial oil passage PR12. This pilot pressure acts on the arm control pilot port 20P1 of the arm control valve 20. When the arm input member 63 is tilted rearward, the pressure control valve 62 is operated and pilot pressure is output from the pressure control valve 62 to the partial oil passage PR13. This pilot pressure acts on the arm control pilot port 20P2 of the arm control valve 20.

[0024] More specifically, when an operation for raising the arm 45 is performed by the arm input member 63 (an operation for tilting the arm input member 63 backward), the pilot pressure applied to the arm control pilot port 20P1 becomes higher than the predetermined pressure than the pilot pressure applied to the arm control pilot port 20P2. When an operation for lowering the arm 45 is performed by the arm input member 63 (an operation for tilting the arm input member 63 forward), the pilot pressure applied to the arm control pilot port 20P2 becomes higher than the predetermined pressure than the pilot pressure applied to the arm control pilot port 20P1. When the operation amount of the arm input member 63 is smaller than a predetermined threshold amount, the absolute value of the difference between the pilot pressure applied to the arm control pilot port 20P2 and the pilot pressure applied to the arm control pilot port 20P1 becomes equal to or smaller than the predetermined pressure. The arm operation detection sensors AS1 and AS2 are configured to detect the arm input member 63. The arm operation detection sensor AS1 is, for example, a pressure switch connected to the partial oil passage PR12. When the pilot pressure in the partial oil passage PR12 exceeds a predetermined pressure, the arm operation detection sensor AS1 outputs a predetermined electric signal to the control device 15. When the pilot pressure in the partial oil passage PR13 exceeds a predetermined pressure, the arm operation detection sensor AS2 outputs a predetermined electric signal to the control device 15.

[0025] The second pilot oil passage PR2 connects bucket control pilot ports 25P1, 25P2 and second hydraulic pump 12. Specifically, the second pilot oil passage PR2 includes a partial oil passage PR10 that extends from second hydraulic pump 12 to joint J21 and is common to the first pilot oil passage PR1, a partial oil passage PR21 that extends from the joint J21 to the bucket pilot control valve 65, a partial oil passage PR22 that extends from the bucket pilot control valve 65 to bucket control pilot port 25P1, and a partial oil passage PR23 that extends from the bucket pilot control valve 65 to bucket control pilot port 25P2. The bucket pilot control valve 65 is provided in the second pilot oil passage PR2, and controls the hydraulic pressure of the pilot oil applied to bucket control pilot ports 25P1, 25P2, based on the operation amount of a bucket input member 68 that is operated to swing the bucket 41. Specifically, the bucket pilot control valve 65 includes a pressure control valve 66 connected to the partial oil passage PR22, and a pressure control valve 67 connected to the partial oil passage PR23.

[0026] When the bucket input member 68 is tilted to the right, the pressure control valve 66 is operated and pilot pressure is output from the pressure control valve 66 to the partial oil passage PR22. This pilot pressure acts on bucket control pilot port 25P1 of the bucket control valve 25. When the bucket input member 68 is tilted to the left, the pressure control valve 67 is operated and pilot pressure is output from the pressure control valve 67 to the partial oil passage PR23. This pilot pressure acts on bucket control pilot port 25P2 of the bucket control valve 25.

[0027] More specifically, when an operation is performed by bucket input member 68 to tilt bucket tip 41D downward (an operation to tilt bucket input member 68 to the right), the pilot pressure applied to bucket control pilot port 25P1 becomes greater than the predetermined pressure than the pilot pressure applied to bucket control pilot port 25P2. When an operation is performed by bucket input member 68 to tilt bucket tip 41D upward (an operation to tilt bucket input member 68 to the left), the pilot pressure applied to bucket control pilot port 25P2 becomes greater than the predetermined pressure than the pilot pressure applied to bucket control pilot port 25P1. When the operation amount of bucket input member 68 is smaller than a predetermined threshold amount, the absolute value of the difference between the pilot pressure applied to bucket control pilot port 25P2 and the pilot pressure applied to bucket control pilot port 25P1 becomes equal to or less than the predetermined pressure.

[0028] 3, arm input member 63 and bucket input member 68 are shown as separate members, but they may be the same member. In this case, pressure control valves 61, 62, 66, 67 are arranged around the same member. Bucket operation detection sensor BS1 outputs a predetermined electric signal to control device 15 when the pilot pressure in partial oil passage PR22 exceeds a predetermined pressure. Bucket operation detection sensor BS2 outputs a predetermined electric signal to control device 15 when the pilot pressure in partial oil passage PR23 exceeds a predetermined pressure.

[0029] The bypass oil passage BR1 is configured to connect the fourth oil passage R4 and the first oil passage R1. The bypass oil passage BR1 is connected to the fourth oil passage R4 at the first joint J1. The bypass oil passage BR1 is connected to the first oil passage R1 at the third joint J3. The switching mechanism 70 is configured to control the connection and disconnection of the fourth oil passage R4 and the first oil passage R1 by the bypass oil passage BR1. The control device 15 is configured to determine whether or not an uptilt operation for raising the arm 45 and tilting the bucket 41 downward has been performed based on the output of the arm operation detection sensors AS1 and AS2 and the output of the bucket operation detection sensors BS1 and BS2, and to control the switching mechanism 70 to connect the fourth oil passage R4 and the first oil passage R1 when it is determined that an uptilt operation has been performed. The control device 15 is, for example, a hardware controller such as an ECU. Therefore, the control device 15 includes electronic circuits such as a hardware processor and a memory.

[0030] The switching mechanism 70 includes a solenoid valve 71 and a first switching valve 72. The first switching valve 72 is provided in a fourth oil passage R4 between the first joint J1 and the arm control valve 20, and has a first pilot port PP1. The first switching valve 72 is configured to cut off the connection between the arm control valve 20 and the fourth chamber CB4 of the arm cylinder 48 via the fourth oil passage R4 when a pilot oil pressure equal to or greater than the first threshold pressure is applied to the first pilot port PP1, and to connect the arm control valve 20 and the fourth chamber CB4 via the fourth oil passage R4 when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port PP1. The solenoid valve 71 is switchable between a second position VP2 that communicates the first pilot port PP1 with the hydraulic oil tank 10 and a first position VP1 that connects the first pilot port PP1 to an oil passage that can apply a pilot pressure equal to or greater than the first threshold pressure to the first pilot port PP1.

[0031] A control device 15 is connected to a solenoid of the solenoid valve 71. When, for example, the pilot pressure of the partial oil passage PR12 obtained from the arm operation detection sensor AS1 is higher than the pilot pressure of the partial oil passage PR13 obtained from the arm operation detection sensor AS1 by more than a first threshold pressure and the pilot pressure of the partial oil passage PR22 obtained from the bucket operation detection sensor BS1 is higher than the pilot pressure of the partial oil passage PR23 obtained from the bucket operation detection sensor BS2, the control device 15 determines that an uptilt operation has been performed and transmits an electric signal to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1.

[0032] Furthermore, the work machine 1 further includes an ON / OFF switch 16 connected to the control device 15. When the switch 16 is switched ON, the control device 15 transmits an electric signal to the solenoid valve 71 to switch the solenoid valve 71 to a first position VP1. This switch 16 is switched ON when performing horizontal control to keep the direction from the bucket pivot shaft 43 to the bucket tip 41D approximately parallel to the horizontal plane by changing the tilt angle of the bucket tip 41D in response to the elevation angle of the arm 45 relative to the vehicle body 2.

[0033] The work machine 1 further includes an additional bypass oil passage BR2 that connects the fourth oil passage R4 between the first changeover valve 72 and the arm control valve 20 and the second oil passage R2. The additional bypass oil passage BR2 connects to the fourth oil passage R4 at the second joint J2 and connects to the second oil passage R2 at the fourth joint J4. The changeover mechanism 70 further includes a second changeover valve 73 provided in the bypass oil passage BR1 and a third changeover valve 74 provided in the additional bypass oil passage BR2. The bypass oil passage BR1 includes a partial oil passage BR10 from the first joint J1 to the second changeover valve 73 and a partial oil passage BR11 from the second changeover valve 73 to the third joint J3. The additional bypass oil passage BR2 includes a partial oil passage BR20 from the second joint J2 to the third changeover valve 74 and a partial oil passage BR21 from the third changeover valve 74 to the fourth joint J4. The work machine 1 further includes a first connection passage CR1 connecting an additional bypass oil passage BR2 (partial oil passage BR20) between the second joint J2 and the third switching valve 74 and the second switching valve 73, a second connection passage CR2 connecting a bypass oil passage BR1 (partial oil passage BR11) between the third joint J3 and the second switching valve 73 and the third switching valve 74, and a third connection passage CR3 connecting the bypass oil passage BR1 (partial oil passage BR11) between the second connection passage CR2 and the second switching valve 73 and the second switching valve 73.

[0034] The second changeover valve 73 is configured to switch to a first communication position CP1 that communicates the first joint J1 and the third joint J3 when a first hydraulic pressure in a bypass oil passage BR1 (partial oil passage BR10) between the first joint J1 and the second changeover valve 73 is greater than a second hydraulic pressure in the first connection passage CR1, and to switch to a first blocking position BP1 that blocks communication between the first joint J1 and the third joint J3 when the second hydraulic pressure is equal to or less than the first hydraulic pressure. The second changeover valve 73 is configured to connect the partial oil passage BR10 and the first connection passage CR1 when switched to the first blocking position BP1. The second changeover valve 73 is configured to block the partial oil passage BR10 and the first connection passage CR1 when switched to the first communication position CP1.

[0035] The third changeover valve 74 is switched to any one of a second cutoff position BP2, a 21st communication position CP21, and a 22nd communication position CP22 based on a third oil pressure in an additional bypass oil passage BR2 (partial oil passage BR20) between the second joint J2 and the third changeover valve 74 and a fourth oil pressure in the second connection passage CR2. The 21st communication position CP21 and the 22nd communication position CP22 are collectively referred to as the second communication position CP2. Since a check valve CKV is provided between the second connection passage CR2 and the third joint J3, the oil pressure in the first oil passage R1 does not affect the oil pressure in the second connection passage CR2. The third changeover valve 74 is configured to switch to a second communication position CP2 that communicates the second joint J2 and the fourth joint J4 when the third hydraulic pressure is lower than the fourth hydraulic pressure, and to switch to a second blocking position BP2 that blocks communication between the second joint J2 and the fourth joint J4 when the fourth hydraulic pressure is equal to or lower than the third hydraulic pressure. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is lower than a predetermined pressure, the third changeover valve 74 switches to a 21st communication position CP21 to communicate the second joint J2 and the fourth joint J4 and block the connection between the third connection passage CR3 and the partial oil passage BR11. On the other hand, when the third hydraulic pressure is lower than the fourth hydraulic pressure by a predetermined pressure or more, the third changeover valve 74 switches to the 21st communication position CP21 to communicate the second joint J2 and the fourth joint J4 and connect the third connection passage CR3 and the bypass oil passage BR1 (partial oil passage BR11). This makes it possible to prevent the hydraulic pressure in the bypass oil passage BR1 (partial oil passage BR11) from becoming too high.

[0036] Furthermore, the work machine 1 further includes a first drain oil passage DR1 that connects the fourth chamber CB4 and the hydraulic oil tank 10 when the arm control valve 20 and the fourth chamber CB4 of the arm cylinder 48 are connected via the fourth oil passage R4 by the first changeover valve 72. The changeover mechanism 70 further includes a first counterbalance valve BV1 provided in the first drain oil passage DR1, a fourth changeover valve 75, a third pilot oil passage PR3 that connects the fourth changeover valve 75 and the first pilot port PP1 of the first changeover valve 72, a fourth pilot oil passage PR4 that connects the first drain oil passage DR1 between the first changeover valve 72 and the first counterbalance valve BV1 and the fourth changeover valve 75, and a second drain oil passage DR2 that connects the fourth changeover valve 75 and the hydraulic oil tank 10. The first counterbalance valve BV1 is a pressure control valve that opens when the pressure at the illustrated joint J8 becomes higher than the pressure at the joint J9 by a predetermined pressure or more, and is configured to allow hydraulic oil to flow from the joint J8 to the joint J9. The first threshold pressure is lower than the predetermined pressure at which the first counterbalance valve BV1 opens. The same counterbalance valves BV2-BV4 are connected to fourth to sixth drain oil passages DR4-DR6 that are connected to the third oil passage R3, the first oil passage R1, and the second oil passage R2, respectively. The fourth to sixth drain oil passages DR4-DR6 are connected to the first drain oil passage DR1.

[0037] The fourth switching valve 75 includes a first connection port ZP1 connected to the third pilot oil passage PR3, a second connection port ZP2 connected to the fourth pilot oil passage PR4, a third connection port ZP3 connected to the second drain oil passage DR2, and a switching valve pilot port 75P to which pilot pressure is applied by the solenoid valve 71. When pilot oil pressure equal to or greater than the second threshold pressure is applied to the switching valve pilot port 75P, the fourth switching valve 75 is switched to a drain position DP that connects the first connection port ZP1, the second connection port ZP2, and the third connection port ZP3. When pilot oil pressure smaller than the second threshold pressure is applied to the switching valve pilot port 75P, the fourth switching valve 75 is switched to a pressure increase position UP that connects the first connection port ZP1 and the second connection port ZP2 and disconnects the third connection port ZP3 from the first connection port ZP1 and the second connection port ZP2.

[0038] When the solenoid valve 71 is switched to the second position VP2 by the control device 15, a pilot oil pressure equal to or greater than the second threshold pressure is applied to the switching valve pilot port 75P. Therefore, the fourth switching valve 75 is switched to the drain position DP, and the pilot pressure applied to the first pilot port PP1 falls below the first threshold pressure. At this time, the first switching valve 72 is opened, and the arm control valve 20 and the fourth chamber CB4 are connected via the fourth oil passage R4, and the fourth oil passage R4 is connected to the first drain oil passage DR1 to the first counterbalance valve BV1.

[0039] At this time, when the arm input member 63 is tilted forward, the pilot pressure applied to the arm control pilot port 20P1 becomes greater than the pilot pressure applied to the arm control pilot port 20P2 and is greater than the above-mentioned predetermined pressure, so that the arm control valve 20 is switched to the arm cylinder extended control position AEP. Therefore, the hydraulic oil having a pressure exceeding the third threshold pressure from the first hydraulic pump 11 is sent to the third chamber CB3 of the arm cylinder 48 via the arm control valve 20. As a result, the hydraulic oil is output from the fourth chamber CB4 of the arm cylinder 48 to the fourth oil passage R4. Since the first switching valve 72 is opened, the hydraulic oil is sent to the second arm control valve port XP2 of the arm control valve 20 and discharged to the third drain oil passage DR3 connected to the first drain oil passage DR1.

[0040] Furthermore, when the arm input member 63 is tilted rearward, the pilot pressure applied to the arm control pilot port 20P2 becomes greater than the pilot pressure applied to the arm control pilot port 20P1 and is greater than the above-mentioned predetermined pressure, so that the arm control valve 20 is switched to the arm cylinder contraction control position ASP. Therefore, hydraulic oil having a pressure exceeding the third threshold pressure from the first hydraulic pump 11 is sent to the fourth chamber CB4 of the arm cylinder 48 via the arm control valve 20 and the first switching valve 72. As a result, hydraulic oil is output from the third chamber CB3 of the arm cylinder 48 to the third oil passage R3. The hydraulic oil is sent to the third arm control valve port XP3 of the arm control valve 20 and discharged to the third drain oil passage DR3 connected to the first drain oil passage DR1.

[0041] When the solenoid valve 71 is switched to the second position VP2 by the control device 15, the control of the bucket 41 is performed independently of the control of the arm 45, except for the uptilt operation. In this state, when the bucket input member 68 is tilted to the right, the pilot pressure applied to the bucket control pilot port 25P1 becomes greater than the pilot pressure applied to the bucket control pilot port 25P2 and is greater than the above-mentioned predetermined pressure, so that the bucket control valve 25 is switched to the bucket cylinder extension control position BEP. Therefore, hydraulic oil having a pressure exceeding the fourth threshold pressure from the first hydraulic pump 11 is sent to the first chamber CB1 of the bucket cylinder 49 via the bucket control valve 25. As a result, the hydraulic oil is output from the second chamber CB2 of the bucket cylinder 49 to the second oil passage R2. The hydraulic oil is sent to the third bucket control valve port YP3 of the bucket control valve 25 and discharged to the seventh drain oil passage DR7 connected to the first drain oil passage DR1.

[0042] Furthermore, when bucket input member 68 is tilted to the left, the pilot pressure applied to bucket control pilot port 25P2 becomes greater than the pilot pressure applied to bucket control pilot port 25P1 and is greater than the above-mentioned predetermined pressure, so that bucket control valve 25 is switched to bucket cylinder retraction control position BSP. As a result, hydraulic oil with a pressure exceeding the fourth threshold pressure from first hydraulic pump 11 is sent to second chamber CB2 of bucket cylinder 49 via bucket control valve 25. As a result, hydraulic oil is output from the first chamber CB1 of bucket cylinder 49 to first oil passage R1. The hydraulic oil is sent to second bucket control valve port YP2 of bucket control valve 25 and discharged to seventh drain oil passage DR7 connected to first drain oil passage DR1.

[0043] When the solenoid valve 71 is switched to the first position VP1 by the control device 15 after the solenoid valve 71 is switched to the second position VP2 by the control device 15, a pilot oil pressure smaller than the second threshold pressure is applied to the switching valve pilot port 75P, and the fourth switching valve 75 is switched to the pressure increase position UP. At the beginning of the switching, the pilot pressure applied to the first pilot port PP1 is lower than the first threshold pressure, but the pilot pressure is immediately increased by the pressure of the hydraulic oil flowing from the fourth oil passage R4. Since the predetermined pressure at which the first counterbalance valve opens is higher than the first threshold pressure, the pilot pressure exceeds the first threshold pressure, and the first switching valve 72 is closed. As a result, the connection between the arm control valve 20 and the fourth chamber CB4 of the arm cylinder 48 via the fourth oil passage R4 is cut off.

[0044] When first changeover valve 72 is closed, an operation is performed to lift arm 45 (an operation to tilt arm input member 63 rearward) and no operation is performed on bucket 41 (an operation to not tilt bucket input member 68 anywhere), arm control valve 20 is switched to arm cylinder extension control position AEP, and bucket control valve 25 is switched to bucket cylinder stationary control position BNP. When arm input member 63 and bucket input member 68 are the same, this operation refers to an operation in which the same input member is tilted rearward without being tilted left or right.

[0045] At this time, as described above, the hydraulic oil flows out of the fourth chamber CB4 of the arm cylinder 48, but because the first changeover valve 72 is closed, it flows from the first joint J1 to the second changeover valve 73. In addition, because the additional bypass oil passage BR2 and the first connection passage CR1 connected thereto are connected to the third drain oil passage DR3, the first hydraulic pressure in the bypass oil passage BR1 (partial oil passage BR10) between the first joint J1 and the second changeover valve 73 is greater than the second hydraulic pressure in the first connection passage CR1. As a result, the second changeover valve 73 is switched to the first communication position CP1. At this time, the hydraulic oil is sent from the second changeover valve 73 to the first chamber CB1 of the bucket cylinder 49 via the bypass oil passage BR1 (partial oil passage BR11) and the first oil passage R1 (partial oil passage R13). At this time, the hydraulic oil is output from the second chamber CB2 of the bucket cylinder 49 to the second oil passage R2 and the additional bypass oil passage BR2 (partial oil passage BR21), but initially, since the third changeover valve 74 is located at the second cutoff position BP2, the hydraulic oil cannot flow, and the hydraulic pressure of the second connection passage CR2 rises. When the difference between the fourth hydraulic pressure of the second connection passage CR2 and the third hydraulic pressure of the additional bypass oil passage BR2 (partial oil passage BR20) exceeds the connection threshold pressure, the second connection passage CR2 is switched to either the 21st communication position CP21 or the 22nd communication position CP22 based on the difference between the third hydraulic pressure of the additional bypass oil passage BR2 (partial oil passage BR20) and the fourth hydraulic pressure of the second connection passage CR2. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is smaller than a predetermined switching threshold, the third changeover valve 74 is switched to the 21st communication position CP21. When the difference between the fourth hydraulic pressure and the third hydraulic pressure is equal to or greater than a predetermined switching threshold, the third changeover valve 74 is switched to the 22nd communication position CP22. When the third changeover valve 74 is switched to the 21st communication position CP21 or the 22nd communication position CP22, the hydraulic oil output from the second chamber CB2 of the bucket cylinder 49 is discharged to the hydraulic oil tank 10 via the additional bypass oil passage BR2 and the third drain oil passage DR3.

[0046] However, when the hydraulic oil flows out of the fourth chamber CB4 of the arm cylinder 48, the second hydraulic pressure of the first connection passage CR1 rises, and when the second switching valve 73 is switched to the first cut-off position BP1, the hydraulic oil flowing out of the fourth chamber CB4 is discharged to the hydraulic oil tank 10 via the first connection passage CR1, the additional bypass oil passage BR2, and the third drain oil passage DR3. Therefore, a part of the amount of oil discharged from the fourth chamber CB4 of the arm cylinder 48 by flowing into the third chamber CB3 of the arm cylinder 48 flows into the first chamber CB1 of the bucket cylinder 49, and the remainder is discharged to the hydraulic oil tank 10. The size of the throttle of the first cut-off position BP1 of the second switching valve 73 is empirically adjusted so that the change in the elevation angle of the arm 45 with respect to the vehicle body 2 and the change in the swing angle with respect to the arm 45 per unit amount of hydraulic oil are substantially equal to each other, and the amount discharged to the hydraulic oil tank 10 is adjusted. Therefore, the swing angle of the bucket tip 41D relative to the arm 45 is changed in response to the elevation angle of the arm, and the direction from the bucket pivot shaft 43 to the bucket tip 41D is controlled to be approximately horizontal. This type of control is called horizontal control.

[0047] When the first switching valve 72 is closed, an operation to lower the arm 45 is performed (an operation to tilt the arm input member 63 forward) and no operation is performed on the bucket 41 (an operation to not tilt the bucket input member 68 anywhere), the arm control valve 20 is switched to the arm cylinder contraction control position ASP, and the bucket control valve 25 is switched to the bucket cylinder stationary control position BNP. At this time, hydraulic oil having a pressure exceeding the third threshold pressure from the first hydraulic pump 11 is output from the second arm control valve port XP2. Since this third threshold pressure is greater than the above-mentioned first threshold pressure and the threshold pressure for opening the first counterbalance valve BV1, the hydraulic oil is sent to the fourth chamber CB4 of the arm cylinder 48 through the fourth oil passage R4 by pushing and opening the first switching valve 72. At this time, the hydraulic oil is discharged from the third chamber CB3 of the arm cylinder 48 through the third oil passage R3 and the third drain oil passage DR3 to the hydraulic oil tank 10.

[0048] When the solenoid valve 71 is switched to the first position VP1 by the control device 15, the control of the bucket 41 is performed independently of the control of the arm 45, except for the uptilt operation. These methods have been described above and will not be described again. Next, the uptilt operation will be described. The uptilt operation refers to an operation in which the arm 45 is raised (an operation in which the arm input member 63 is tilted forward) and the bucket 41 is tilted downward (an operation in which the bucket input member 68 is tilted to the right). When the arm input member 63 and the bucket input member 68 are the same, this operation refers to an operation in which the same input member is tilted to the right and forward. This operation can be detected from the outputs of the arm operation detection sensors AS1, AS2 and the bucket operation detection sensors BS1, BS2.

[0049] For example, it can be determined that an uptilt operation has been performed when the pilot pressure of partial oil passage PR12 detected by arm operation detection sensor AS1 is higher than a predetermined pressure (arm operation detection sensor AS1 transmits a predetermined signal), and the pilot pressure of partial oil passage PR13 detected by arm operation detection sensor AS2 is lower than the predetermined pressure (arm operation detection sensor AS2 does not transmit the predetermined signal), and the pilot pressure of partial oil passage PR22 detected by bucket operation detection sensor BS1 is higher than a predetermined pressure (bucket operation detection sensor BS1 transmits a predetermined signal) and is lower than the predetermined pressure than the pilot pressure of partial oil passage PR13 detected by bucket operation detection sensor BS2 (bucket operation detection sensor BS1 does not transmit the predetermined signal). The control device 15 acquires the outputs of the arm operation detection sensors AS1, AS2 and the bucket operation detection sensors BS1, BS2, and determines whether or not an uptilt operation has been performed. When it is determined that an uptilt operation has been performed, regardless of the setting of the ON / OFF changeover switch 16, the controller 15 transmits an electric signal to the solenoid valve 71 to switch the solenoid valve 71 to the first position VP1.

[0050] When an uptilt operation is performed, the arm control valve 20 is switched to the arm cylinder extension control position AEP, and the bucket control valve 25 is switched to the bucket cylinder extension control position BEP. At this time, as in the case of horizontal control, the hydraulic oil flowing out from the fourth chamber CB4 of the arm cylinder 48 is sent to the first chamber CB1 of the bucket cylinder 49. Furthermore, the hydraulic oil having a pressure exceeding the fourth threshold pressure from the first hydraulic pump 11 is sent to the first chamber CB1 of the bucket cylinder 49 via the bucket control valve 25. Therefore, the tilt speed of the bucket 41 increases, and the responsiveness of the uptilt operation is improved. The hydraulic oil output from the second chamber CB2 of the bucket cylinder 49 is discharged to the seventh drain oil passage DR7 as in the case described above. <Method of controlling work equipment>

[0051] Next, a control method of the working machine 1 according to this embodiment will be described. FIG. 4 is a flowchart showing the control method of the working machine 1. In step S1, the control device 15 of the working machine 1 detects the operation of the arm input member 63 operated to raise and lower the arm 45. Specifically, the control device 15 detects an operation of raising the arm 45 (first operation), an operation of lowering the arm 45, and an operation of stopping the arm 45 based on the output from the arm operation detection sensors AS1 and AS2. For example, the control device 15 can detect the operation of raising the arm 45 by receiving a predetermined signal from the arm operation detection sensor AS1 and not receiving the predetermined signal from the arm operation detection sensor AS2. The control device 15 can detect the operation of lowering the arm 45 by receiving a predetermined signal from the arm operation detection sensor AS2 and not receiving the predetermined signal from the arm operation detection sensor AS1. The control device 15 can detect the operation of stopping the arm 45 by not receiving a predetermined signal from the arm operation detection sensor AS1 and not receiving the predetermined signal from the arm operation detection sensor AS2.

[0052] When an operation to raise the arm 45 is detected in step S1, in step S2, the work machine 1 sends hydraulic oil from the first hydraulic pump 11 to the third chamber CB3 of the arm cylinder 48 via the third oil passage R3 to raise the arm tip portion 45D of the arm 45 that swingably supports the bucket base end portion 41P opposite to the bucket tip portion 41D of the bucket 41. When an operation to lower the arm 45 is detected in step S1, in step S3, the work machine 1 communicates the third oil passage R3 from the first hydraulic pump 11 to the arm control valve 20 with the fourth oil passage R4 that connects the arm control valve 20 and the fourth chamber CB4 of the arm cylinder 48 by the arm control valve 20 provided in the third oil passage R3, and sends hydraulic oil from the first hydraulic pump 11 to the fourth chamber CB4 of the arm cylinder 48 to lower the arm tip portion 45D. When an operation to stop the arm 45 is detected in step S1, the work machine 1 switches the arm control valve 20 to the arm cylinder stationary control position ANP in step S4 to control the arm 45 not to move.

[0053] In step S5, the control device 15 of the work machine 1 detects the operation of the bucket input member 68 operated to swing the bucket 41. Specifically, the control device 15 detects an operation of tilting the bucket 41 upward, an operation of tilting the bucket 41 downward (second operation), and an operation of tilting the bucket 41 neither upward nor downward (third operation) based on the outputs from the bucket operation detection sensors BS1 and BS2. For example, the control device 15 can detect an operation of tilting the bucket 41 upward by receiving a predetermined signal from the bucket operation detection sensor BS2 and not receiving the above-mentioned predetermined signal from the bucket operation detection sensor BS1. The control device 15 can detect an operation of tilting the bucket 41 downward (second operation) by receiving a predetermined signal from the bucket operation detection sensor BS1 and not receiving the above-mentioned predetermined signal from the bucket operation detection sensor BS2. When the control device 15 does not receive a specified signal from the bucket operation detection sensor BS1 and does not receive the above-mentioned specified signal from the bucket operation detection sensor BS2, the control device 15 can detect an operation (third operation) that does not tilt the bucket 41 upward or downward.

[0054] When an operation to tilt the bucket 41 upward is detected in step S5, the work machine 1 communicates the first oil passage R1 from the first hydraulic pump 11 to the bucket control valve 25 with the second oil passage R2 connecting the bucket control valve 25 and the second chamber CB2 of the bucket cylinder 49 by the bucket control valve 25 provided in the first oil passage R1 in step S6, and sends hydraulic oil from the first hydraulic pump 11 to the second chamber CB2 of the bucket cylinder 49 to tilt the bucket tip 41D upward. When an operation to tilt the bucket 41 downward (second operation) is detected in step S5, the control device 15 determines in step S7 whether the first operation is detected in step S1. When it is determined that the first operation is not detected (NO in step S7), the work machine 1 sends hydraulic oil from the first hydraulic pump 11 to the first chamber CB1 of the bucket cylinder 49 through the first oil passage R1 in step S8 to tilt the bucket tip 41D of the bucket 41 downward. When the first operation and the second operation are detected (YES in step S7), the work machine 1 sends hydraulic oil to the first chamber CB1 via the first oil passage R1, and connects the fourth oil passage R4 and the first oil passage R1 via the bypass oil passage BR1 by the switching mechanism 70, and sends the hydraulic oil in the fourth oil passage R4 to the first oil passage R1.

[0055] When the third operation is detected in step S5, the work machine 1 detects whether or not the horizontal control is instructed by detecting whether the ON / OFF changeover switch 16 is set to ON in step S10. Furthermore, the work machine 1 determines whether or not the first operation is detected in step S1. When the horizontal control is not instructed or the first operation is not detected (NO in step S10), the work machine 1 controls the bucket control valve 25 to the bucket cylinder stationary control position BNP in step S11 so as not to swing the bucket 41. When the horizontal control is instructed and the first operation and the third operation are detected (YES in step S10), the work machine 1 disconnects the first oil passage R1 by the bucket control valve 25 in step S12, connects the fourth oil passage R4 and the first oil passage R1 by the switching mechanism 70, and sends the hydraulic oil in the fourth chamber CB4 to the first chamber CB1. <Effects of the embodiment>

[0056] The control device 15 of the working machine 1 according to this embodiment is configured to determine whether or not an uptilt operation has been performed to raise the arm 45 and tilt the bucket 41 downward, based on the outputs of the arm operation detection sensors AS1 and AS2 and the bucket operation detection sensors BS1 and BS2, and to control the switching mechanism 70 to connect the fourth oil passage R4 and the first oil passage R1 when it is determined that an uptilt operation has been performed. In the control method of the working machine 1 according to this embodiment, when a first operation to raise the arm 45 and a second operation to tilt the bucket 41 downward are detected, the hydraulic oil is sent to the first chamber CB1 via the first oil passage R1, and the fourth oil passage R4 and the first oil passage R1 are connected by the switching mechanism 70, and the hydraulic oil in the fourth chamber CB4 is sent to the first chamber CB1. This makes it possible to provide a working machine 1 and a control method of the working machine that can achieve the same degree of operability in the uptilt operation whether or not the horizontal control is enabled.

[0057] In this application, the term "comprises" and its derivatives are open-ended terms that describe the presence of elements and do not exclude the presence of other elements not listed. This also applies to the terms "have", "include" and their derivatives.

[0058] The terms "member," "part," "element," "body," and "structure" may have multiple meanings, such as a single part or multiple parts.

[0059] Ordinal numbers such as "first" and "second" are merely terms used to identify components and do not have any other meaning (such as a particular order). For example, the presence of a "first element" does not imply the presence of a "second element," and the presence of a "second element" does not imply the presence of a "first element."

[0060] Words expressing degree, such as "substantially," "about," and "approximately," may mean a reasonable deviation that does not significantly change the final result, unless otherwise specified in the embodiment. All numerical values ​​described in this application may be interpreted to include words such as "substantially," "about," and "approximately."

[0061] In this application, the phrase "at least one of A and B" should be interpreted as including A only, B only, and both A and B.

[0062] It is apparent that various changes and modifications of the present invention are possible in light of the above disclosure, and therefore, the present invention may be practiced otherwise than as specifically disclosed herein without departing from the spirit and scope of the present invention.

Claims

1. a bucket including a bucket base end and a bucket tip end opposite the bucket base end; an arm including an arm tip portion that swingably supports the bucket base end portion and an arm base end portion opposite to the arm tip portion; a vehicle body that supports the arm base end portion so as to be swingable; a bucket cylinder including a first chamber into which hydraulic oil flows when the bucket tip is tilted downward and a second chamber into which hydraulic oil flows when the bucket tip is tilted upward; an arm cylinder including a third chamber into which hydraulic oil flows when the arm tip portion is raised and a fourth chamber into which hydraulic oil flows when the arm tip portion is lowered; A first hydraulic pump configured to discharge hydraulic oil to the bucket cylinder and the arm cylinder; a first oil passage connecting the first hydraulic pump and a first chamber of the bucket cylinder; a bucket control valve that is provided in the first oil passage, has a bucket control pilot port, and is configured to control hydraulic oil supplied to the first chamber and the second chamber in response to a hydraulic pressure of pilot oil applied to the bucket control pilot port; a second oil passage connecting the bucket control valve and the second chamber; a third oil passage connecting the first hydraulic pump and the third chamber of the arm cylinder; an arm control valve that is provided in the third oil passage, has an arm control pilot port, and is configured to control the hydraulic oil supplied to the third chamber and the fourth chamber in response to the hydraulic pressure of the pilot oil applied to the arm control pilot port; a fourth oil passage connecting the arm control valve and the fourth chamber; a second hydraulic pump configured to discharge pilot oil for controlling the arm control valve and the bucket control valve; a first pilot oil passage connecting the arm control pilot port and the second hydraulic pump; an arm pilot control valve that is provided in the first pilot oil passage and controls the hydraulic pressure of the pilot oil applied to the arm control pilot port based on an operation amount of an arm input member that is operated to lift and lower the arm; an arm operation detection sensor configured to detect an operation of the arm input member; a second pilot oil passage connecting the bucket control pilot port and the second hydraulic pump; a bucket pilot control valve that is provided in the second pilot oil passage and controls the hydraulic pressure of the pilot oil applied to the bucket control pilot port based on an operation amount of a bucket input member that is operated to swing the bucket; a bucket operation detection sensor for detecting an operation of the bucket input member; A bypass oil passage configured to connect the fourth oil passage and the first oil passage; A switching mechanism configured to control connection and disconnection between the fourth oil passage and the first oil passage by the bypass oil passage; a control device configured to determine whether or not an uptilt operation for raising the arm and tilting the bucket downward has been performed based on an output of the arm operation detection sensor and an output of the bucket operation detection sensor, and to control the switching mechanism to connect the fourth oil line and the first oil line when it is determined that the uptilt operation has been performed; A work machine comprising:

2. The switching mechanism includes: a first switching valve that is provided in the fourth oil passage between a first joint that connects the bypass oil passage and the fourth oil passage and the arm control valve, has a first pilot port, and is configured to cut off the connection between the arm control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure equal to or greater than a first threshold pressure is applied to the first pilot port, and to connect the arm control valve and the fourth chamber via the fourth oil passage when a pilot oil pressure smaller than the first threshold pressure is applied to the first pilot port; a solenoid valve switchable between a first position that communicates the first pilot port with a hydraulic oil tank and a second position that connects the first pilot port with an oil passage that can apply a pilot pressure equal to or greater than the first threshold pressure to the first pilot port; The work machine according to claim 1 .

3. An additional bypass oil passage is provided connecting the fourth oil passage between the first switching valve and the arm control valve and the second oil passage, The switching mechanism includes: A second switching valve provided in the bypass oil passage; A third switching valve provided in the additional bypass oil passage; Further equipped with The working machine is a first connection passage connecting the additional bypass oil passage between a second joint connecting the fourth oil passage and the additional bypass oil passage and the third switching valve, and the additional bypass oil passage between the second switching valve and the third switching valve; a second connection passage connecting the bypass oil passage between a third joint connecting the bypass oil passage and the first oil passage and the second switching valve; and Equipped with the second changeover valve is configured to be switched to a first communication position that communicates the first joint with the third joint when a first hydraulic pressure in the bypass oil passage between the first joint and the second changeover valve is greater than a second hydraulic pressure in the first connection passage, and to be switched to a first blocking position that blocks communication between the first joint and the third joint when the second hydraulic pressure is equal to or less than the first hydraulic pressure, the third switching valve is configured to be switched to a second communicating position that communicates between a fourth joint connecting the second oil passage and the additional bypass oil passage and the second joint when a third oil pressure in the additional bypass oil passage between the second joint and the third switching valve is smaller than a fourth oil pressure in the second connection passage, and to be switched to a second blocking position that blocks communication between the second joint and the fourth joint when the fourth oil pressure is equal to or lower than the third oil pressure. The work machine according to claim 2.

4. a third connection passage connecting the bypass oil passage between the second connection passage and the second switching valve and the third switching valve; the third switching valve connects the third connection line and the bypass oil line when a third oil pressure of the additional bypass oil line between the second joint and the third switching valve is lower than a fourth oil pressure of the second connection line by a predetermined pressure or more. The work machine according to claim 3.

5. a first drain oil passage connecting the fourth oil passage and a hydraulic oil tank when the arm control valve and the fourth chamber are connected via the fourth oil passage by the first switching valve; The switching mechanism includes: a first counterbalance valve provided in the first drain oil passage; A fourth switching valve; a third pilot oil passage connecting the fourth switching valve and a first pilot port of the first switching valve; a fourth pilot oil passage connecting a first drain oil passage between the first switching valve and the first counterbalance valve and the fourth switching valve; a second drain oil passage connecting the fourth switching valve and the hydraulic oil tank; Further equipped with The fourth switching valve is a first connection port connected to the third pilot oil passage; a second connection port connected to the fourth pilot oil passage; a third connection port connected to the second drain oil passage; a switching valve pilot port to which the pilot pressure is applied by the solenoid valve; Equipped with When a pressure of the pilot oil equal to or greater than a second threshold pressure is applied to the switching valve pilot port, the fourth switching valve is switched to a drain position that communicates the first connection port, the second connection port, and the third connection port, and when a pressure of the pilot oil smaller than the second threshold pressure is applied to the switching valve pilot port, the fourth switching valve is switched to a pressure increase position that communicates the first connection port and the second connection port and disconnects the third connection port from the first connection port and the second connection port. A work machine according to any one of claims 2 to 4.

6. The arm control valve is a first arm control valve port connected to the first hydraulic pump via the third oil passage; a second arm control valve port connected to the fourth oil passage; a third arm control valve port connected to the third chamber of the arm cylinder via the third oil passage; the arm control pilot port; Further equipped with When an operation to lift the arm is performed by the arm input member, the pilot pressure applied to the arm control pilot port switches the arm control valve to an arm cylinder extension control position where the arm control valve communicates with the first arm control valve port and the third arm control valve port and where the second arm control valve port communicates with the first drain oil passage, When an operation for lowering the arm is performed by the arm input member, the pilot pressure applied to the arm control pilot port switches the arm control valve to an arm cylinder contraction control position where the arm control valve communicates with the first arm control valve port and the second arm control valve port and where the third arm control valve port communicates with the first drain oil passage, when the operation amount of the arm input member is smaller than a predetermined threshold amount, the arm control valve is switched to an arm cylinder stationary control position that isolates the first arm control valve port, the second arm control valve port, and the third arm control valve port by the pilot pressure applied to the arm control pilot port. A work machine according to claim 5.

7. 7. The work machine according to claim 6, further comprising a first pressure control valve that connects the first arm control valve port to the second arm control valve port or the third arm control valve port only when a pressure applied to the first arm control valve port is equal to or higher than a third threshold pressure.

8. The bucket control valve is a first bucket control valve port connected to the first hydraulic pump via the first oil passage; a second bucket control valve port connected to the first chamber of the bucket cylinder via the first oil passage; a third bucket control valve port connected to the second oil passage; the bucket control pilot port; Further equipped with when an operation to tilt the bucket tip portion downward is performed by the bucket input member, the pilot pressure applied to the bucket control pilot port switches the bucket control valve to a bucket cylinder extension control position that communicates between the first bucket control valve port and the second bucket control valve port and communicates between the third bucket control valve port and the first drain oil passage, when an operation to tilt the bucket tip portion upward is performed by the bucket input member, the pilot pressure applied to the bucket control pilot port switches the bucket control valve to a bucket cylinder contraction control position that communicates between the first bucket control valve port and the third bucket control valve port and communicates between the second bucket control valve port and the first drain oil passage, when the operation amount of the arm input member is smaller than a predetermined threshold amount, the bucket control valve is switched to a bucket cylinder stationary control position that isolates the first bucket control valve port, the second bucket control valve port, and the third bucket control valve port by the pilot pressure applied to the bucket control pilot port. A work machine according to claim 6 or 7.

9. 9. The work machine according to claim 8, further comprising a second pressure control valve that connects the first bucket control valve port to the second bucket control valve port or the third bucket control valve port only when pressure applied to the first bucket control valve port is equal to or higher than a fourth threshold pressure.

10. A switch for turning on / off the bucket horizontal control is further provided, the switch being electrically connected to the control device. When the horizontal control is set by the switch, the control device switches the solenoid valve to a first position. A work machine according to claim 8 or 9.

11. During the horizontal control, the arm control valve is switched to the arm cylinder extension control position, the bucket control valve is switched to the bucket cylinder stationary control position; A work machine according to claim 10.

12. a change in an elevation angle of the arm with respect to the vehicle body per unit amount of hydraulic oil flowing into the third chamber of the arm cylinder is substantially equal to a swing angle of the bucket tip portion with respect to the arm per unit amount of hydraulic oil flowing into the first chamber of the bucket cylinder. A work machine according to claim 11.

13. When it is determined that the uptilt operation has been performed, the arm control valve is switched to the arm cylinder extension control position, the bucket control valve is switched to the bucket cylinder extension control position; A work machine according to any one of claims 8 to 12.

14. an additional solenoid valve provided in at least one of the first pilot oil passage between the second hydraulic pump and the arm pilot control valve and the second pilot oil passage between the second hydraulic pump and the bucket pilot control valve, and capable of changing a pressure of the hydraulic oil output from the second hydraulic pump; A work machine according to any one of claims 1 to 13.

15. Hydraulic oil is sent from the first hydraulic pump through the first oil passage to the first chamber of the bucket cylinder to tilt a tip portion of the bucket downward, a bucket control valve provided in the first oil passage communicates the first oil passage from the first hydraulic pump to the bucket control valve with a second oil passage that connects the bucket control valve and a second chamber of the bucket cylinder, and the hydraulic oil from the first hydraulic pump is sent to the second chamber of the bucket cylinder to tilt the tip of the bucket upward; hydraulic oil is sent from the first hydraulic pump to a third chamber of an arm cylinder via a third oil passage to raise an arm tip portion of an arm that swingably supports a bucket base end portion opposite to the bucket tip portion of the bucket; an arm control valve provided in the third oil passage communicates the third oil passage from the first hydraulic pump to the arm control valve with a fourth oil passage connecting the arm control valve and a fourth chamber of the arm cylinder, and the hydraulic oil from the first hydraulic pump is sent to the fourth chamber of the arm cylinder to lower the arm tip portion, detecting that a first operation for lifting the arm has been input to an arm input member that is operated for lifting and lowering the arm; detecting that a second operation for tilting the bucket downward has been input to a bucket input member that is operated to swing the bucket; When the first operation and the second operation are detected, hydraulic oil is sent to the first chamber through the first oil passage, and the fourth oil passage and the first oil passage are connected through a bypass oil passage by a switching mechanism, so that the hydraulic oil in the fourth chamber is sent to the first chamber. A method for controlling a work implement.

16. detecting that a third operation that does not tilt the bucket upward or downward has been input to the bucket input member; When the first operation and the third operation are detected, the bucket control valve disconnects the first oil passage, and the switching mechanism connects the fourth oil passage and the first oil passage to send the hydraulic oil in the fourth chamber to the first chamber. A method for controlling a work machine according to claim 15.

Images