Dump truck

Abstract

To provide a dump truck capable of reducing assembly man-hours.SOLUTION: A dump truck 1 comprises: a cargo box 3 provided to be tiltable with respect to a vehicle body 2; a dump cylinder 23 for tilting the cargo box 3; a hook 8 that is provided rotatably with respect to the vehicle body 2 and is engageable with the cargo box 3 side; a lock cylinder 9 for rotating the hook 8; a main oil passage 36 connected to a hydraulic oil chamber 14 of the lock cylinder 9; a communication oil passage 38 that provides communication between the hydraulic oil chamber 14 of the lock cylinder 9 and a hydraulic oil chamber 23a of the dump cylinder 23 when extension operation of the lock cylinder 9 is completed; a branch oil passage 39 that is branched from the communication oil passage 38 and connected to the main oil passage 36; and a check valve 41 that allows a flow of hydraulic oil flow from the communication oil passage 38 side to the main oil passage 36 side in the branch oil passage 39 and restricts a flow of hydraulic oil from the main oil passage 36 side to the communication oil passage 38 side. The check valve 41 is provided integrally with the lock cylinder 9.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a dump truck. [Background technology]

[0002] For example, the dump truck described in Patent Document 1 is provided with a cargo box tiltably mounted on the vehicle body, a dump cylinder for tilting the cargo box, and a lift-up prevention device for preventing the cargo box from lifting up while traveling. The lift-up prevention device includes an engagement member rotatably mounted on the vehicle body side and engageable with the cargo box side, and a lock cylinder for rotating the engagement member. While the dump truck is traveling, the lock cylinder is held in an extended state by a spring force, so that the engagement member is held in an engaged state with the cargo box side, thereby preventing the cargo box from lifting up with respect to the vehicle body. When tilting the cargo box, hydraulic oil is supplied to the lock cylinder to contract the lock cylinder against the spring force, and the engagement member rotates in a direction to release the engagement with the cargo box side, thereby enabling the dump cylinder to tilt the cargo box.

[0003] In the dump truck of Patent Document 1, it is necessary to extend the dump cylinder to tilt the cargo box after contracting the lock cylinder to release the engagement between the engagement member and the cargo box. For this reason, the hydraulic circuit of the dump truck is provided with a main oil passage (pipe 16) that supplies hydraulic oil discharged from the hydraulic pump to the lock cylinder, and a communication oil passage (communication pipe 18) that communicates the lock cylinder and the dump cylinder when the contraction of the lock cylinder is completed by the hydraulic oil supplied from the main oil passage. As a result, when the contraction of the lock cylinder is completed, the hydraulic oil is supplied from the lock cylinder through the communication oil passage to the dump cylinder, thereby allowing the dump cylinder to be extended.

[0004] In addition, in the dump truck of Patent Document 1, it is necessary to collapse the cargo box by contracting the dump cylinder while maintaining the lock cylinder in a contracted state (a state in which the engagement member is disengaged from the cargo box). For this reason, the hydraulic circuit of the dump truck is provided with a branch oil passage (pipe 21) for supplying a portion of the hydraulic oil discharged from the dump cylinder to the lock cylinder via the communication oil passage and for returning the remainder of the discharged hydraulic oil to the main oil passage by branching off from the middle of the communication oil passage. This allows the dump cylinder to be contracted while maintaining the lock cylinder in a contracted state. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Jpn. Published No. 1 of Showa 46 Summary of the Invention [Problem to be solved by the invention]

[0006] A check valve is provided in the branch oil passage in the hydraulic circuit to regulate the flow of hydraulic oil from the main oil passage to the connecting oil passage. This makes it possible to prevent the dump cylinder from extending and tilting the cargo box while the lock cylinder is contracting (while the engagement between the engagement member and the cargo box is being released). However, since a check valve must be separately installed in the hydraulic circuit, there is a problem that the number of steps required to assemble the dump truck is increased.

[0007] The present invention has been made in consideration of the above circumstances, and has an object to provide a dump truck that can reduce the number of assembly steps. [Means for solving the problem]

[0008] (1) The dump truck of the present invention includes a cargo box tiltably mounted with respect to a vehicle body, a dump cylinder having a first oil chamber through which hydraulic oil is supplied and discharged, and tilting the cargo box, a hook rotatably mounted with respect to the vehicle body and engageable with the cargo box, a lock cylinder having a second oil chamber through which hydraulic oil is supplied and discharged, and rotating the hook, a main oil passage connected to the second oil chamber, a communicating oil passage that communicates the first oil chamber with the second oil chamber when the extension or contraction operation of the lock cylinder is completed, a branch oil passage branching from the communicating oil passage and returning a portion of the hydraulic oil discharged from the first oil chamber to the communicating oil passage to the main oil passage, and a check valve in the branch oil passage that allows the hydraulic oil to flow from the communicating oil passage side to the main oil passage side and regulates the flow of hydraulic oil from the main oil passage side to the communicating oil passage side, and the check valve is provided integrally with the lock cylinder.

[0009] According to the present invention, the check valve that regulates the flow of hydraulic oil from the main oil passage to the communicating oil passage in the branch oil passage branching off from the communicating oil passage is provided integrally with the lock cylinder, so by attaching the lock cylinder integrated with the check valve to the hydraulic circuit, the work of separately attaching the check valve is not required, thereby reducing the number of steps required to assemble the dump truck.

[0010] (2) The lock cylinder has a cylindrical cylinder body in which the second oil chamber is formed, and a wall portion of the cylinder body is formed with a first oil hole constituting a part of the main oil passage, a second oil hole constituting a part of the communicating oil passage, and a third oil hole branching off from a midpoint of the second oil hole and connecting to a midpoint of the first oil hole and constituting the branched oil passage, and it is preferable that the check valve is provided in the third oil hole. In this case, since the branch oil passage is integrally formed in the wall of the cylinder body of the lock cylinder, attaching the lock cylinder to the hydraulic circuit eliminates the need to provide a separate branch oil passage in the hydraulic circuit, which further reduces the number of steps required to assemble the dump truck.

[0011] (3) The lock cylinder preferably has a cylindrical cylinder body and a piston arranged inside the cylinder body so as to be able to reciprocate in the axial direction, and the second oil chamber is formed inside the cylinder body on one axial side of the piston, and a spring is preferably provided to bias the piston toward the one axial side.

[0012] In this case, if the hook is made to engage with the cargo box when the lock cylinder is operated so that the piston moves axially to one side due to the biasing force of the spring, the hook can be indirectly engaged with the cargo box by the biasing force of the spring built into the lock cylinder. As a result, by attaching the lock cylinder to the hydraulic circuit, the work of separately attaching a spring to the hook for engaging the hook with the cargo box is no longer necessary, and the number of steps in assembling the dump truck can be further reduced. Effect of the Invention

[0013] According to the present invention, the number of steps required for assembling a dump truck can be reduced. [Brief description of the drawings]

[0014] [Figure 1] FIG. 2 is a side view showing the rear side of the dump truck according to the embodiment of the present invention. [Diagram 2] FIG. 2 is a side view for explaining a function of the dump truck. [Diagram 3] FIG. 2 is a hydraulic circuit diagram of the dump truck. [Figure 4] FIG. 4 is a schematic cross-sectional view showing the internal configuration of a lock cylinder. [Diagram 5] FIG. 4 is a hydraulic circuit diagram illustrating the flow of hydraulic oil when the packing box is tilted. [Figure 6] FIG. 4 is a hydraulic circuit diagram showing a state in which the extension operation of the lock cylinder has been completed. [Figure 7] FIG. 4 is a hydraulic circuit diagram showing a state in which the extension operation of the dump cylinder has been completed. [Figure 8]FIG. 4 is a hydraulic circuit diagram illustrating the flow of hydraulic oil when a packing box is toppled. [Figure 9] FIG. 4 is a hydraulic circuit diagram showing a state in which the contraction operation of the dump cylinder has been completed. [Figure 10] FIG. 11 is a hydraulic circuit diagram showing a state in which the contraction operation of the lock cylinder has been completed. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. [Overall configuration] Fig. 1 is a side view showing the rear side of a dump truck according to an embodiment of the present invention. Fig. 2 is a side view for explaining the function of the dump truck 1. Hereinafter, in this specification, the front-rear direction, the up-down direction, and the left-right direction refer to the front-rear direction, the up-down direction, and the left-right direction of the dump truck, respectively. In Fig. 1 and Fig. 2, the dump truck 1 includes a vehicle body 2, a cargo box 3, a dump device 5, and a lift-up prevention device 6.

[0016] The vehicle body 2 has a chassis frame 2a and a subframe 2b fixed onto the chassis frame 2a. The cargo box 3 is mounted on the vehicle body 2 and is tiltable relative to the vehicle body 2. Specifically, the cargo box 3 is tiltable via a hinge shaft 4 at the rear end of the subframe 2b.

[0017] The dump device 5 is disposed between the subframe 2b and the cargo box 3. The dump device 5 includes a triangular lift arm 21, a rod-shaped tension link 22, and a dump cylinder 23. One top of the lift arm 21 is rotatably attached to the subframe 2b via a connecting shaft 24. One end of a tension link 22 is rotatably attached to the other top of the lift arm 21 via a connecting shaft 25. The other end of the tension link 22 is rotatably attached to the bottom of the cargo box 3 via a connecting shaft 26.

[0018] One end of a dump cylinder 23 is rotatably attached to the remaining top of the lift arm 21 via a connecting shaft 27. The other end of the dump cylinder 23 is rotatably attached to the bottom of the cargo box 3 via a connecting shaft 28. The dump cylinder 23 is a hydraulic cylinder that tilts and lays down the cargo box 3, and has a hydraulic oil chamber (first oil chamber) 23a into which hydraulic oil is supplied and discharged when the dump cylinder 23 extends and retracts (see FIG. 3).

[0019] When hydraulic oil is supplied to the hydraulic oil chamber 23a of the dump cylinder 23 from the state shown in Fig. 1, the dump cylinder 23 is extended. When the dump cylinder 23 is extended, the lift arm 21 rotates upward about the connecting shaft 24 as shown in Fig. 2, and the cargo box 3 is in a dumped state tilted with the front side raised relative to the vehicle body 2. When hydraulic oil is discharged from the hydraulic oil chamber 23a of the dump cylinder 23 from the dumped state shown in Fig. 2 to contract the dump cylinder 23, the lift arm 21 rotates downward about the connecting shaft 24, and the cargo box 3 is in a landing state in which it is laid down on the vehicle body 2 as shown in Fig. 1.

[0020] The lift-up prevention device 6 is disposed between the subframe 2b and the cargo box 3 forward of the dump device 5, and prevents the cargo box 3 from lifting up relative to the vehicle body 2 due to vibration or the like while the dump truck 1 is traveling. The lift-up prevention device 6 includes a lock pin 7 provided on the cargo box 3 side, a hook 8 rotatably provided with respect to the vehicle body 2 and engageable with the lock pin 7, and a lock cylinder 9 for rotating the hook 8.

[0021] The lock pin 7 is fixed to the bottom of the packing box 3. The base end of the hook 8 is rotatably attached to the subframe 2b via a hinge shaft 10. The tip of the hook 8 is adapted to rotate between an engagement position (FIG. 1) where it engages with the lock pin 7 and a release position (FIG. 2) where it is disengaged from the lock pin 7.

[0022] The lock cylinder 9 is a hydraulic cylinder that rotates the hook 8 between an engaged position and a released position. The lock cylinder 9 has a cylindrical cylinder body 11, a piston 12 (see FIG. 3) that is provided inside the cylinder body 11 so as to be able to reciprocate in the axial direction, and a rod 13 one end of which is fixed to the piston 12. The other end of the rod 13 passes through an end wall of the cylinder body 11 and is connected to the hook 8.

[0023] The cylinder body 11 is attached to the subframe 2b. Inside the cylinder body 11, on the opposite side (one axial side) to the rod 13 side of the piston 12, there is formed a hydraulic oil chamber (second oil chamber) 14 (see FIG. 3) to which hydraulic oil is supplied and discharged. When hydraulic oil is supplied to the hydraulic oil chamber 14 of the cylinder body 11 from the state shown in FIG. 1, the lock cylinder 9 is extended. This causes the hook 8 to rotate to the release position as shown in FIG. 2.

[0024] When hydraulic oil is discharged from the hydraulic oil chamber 14 of the cylinder body 11 from the state shown in Fig. 2, the lock cylinder 9 contracts due to the biasing force of the spring 18, which will be described later. This causes the hook 8 to rotate to the engaged position, as shown in Fig. 1. The hook 8 is held in the engaged position by the biasing force of the spring 18, so that the cargo box 3 is held on the floor by the anti-floating device 6.

[0025] [Hydraulic circuit configuration] 3 is a hydraulic circuit diagram of the dump truck 1. This hydraulic circuit mainly includes an oil tank 31, a hydraulic pump 32, a discharge oil passage 33, a return oil passage 34, a switching valve 35, a main oil passage 36, a bypass oil passage 37, a communication oil passage 38, and a branch oil passage 39. In the following description, the side closer to the hydraulic pump 32 is referred to as the "upstream side", and the side farther from the hydraulic pump 32 is referred to as the "downstream side". In addition, in each of the oil passages 33, 34, 36 to 39, the road end closer to the hydraulic pump 32 is referred to as the "upstream end", and the road end farther from the hydraulic pump 32 is referred to as the "downstream end".

[0026] The hydraulic pump 32 sucks and discharges hydraulic oil in the oil tank 31. The discharge oil passage 33 is connected to the hydraulic pump 32, and the hydraulic oil discharged from the hydraulic pump 32 flows into the discharge oil passage 33. The return oil passage 34 is connected to the oil tank 31, and is an oil passage that returns the hydraulic oil to the oil tank 31.

[0027] The switching valve 35 is, for example, a three-port, three-position switching valve, and the downstream end of the discharge oil passage 33, the downstream end of the return oil passage 34, and the upstream end of the main oil passage 36 are connected to each port. The switching valve 35 is adapted to be switched when an operator operates a switch. When the switching valve 35 is in a neutral position (a center position in FIG. 3), the discharge oil passage 33 communicates with the return oil passage 34, and the main oil passage 36 does not communicate with either the discharge oil passage 33 or the return oil passage 34. When the switching valve 35 is switched from the neutral position to a first position (a position on the left side in FIG. 3), each of the oil passages 33 to 35 is not communicated with any of the other oil passages. When the switching valve 35 is switched from the neutral position to a second position (a position on the right side in FIG. 3), each of the oil passages 33 to 35 is communicated with each of the other oil passages.

[0028] The bypass oil passage 37 branches off from the middle of the discharge oil passage 33 and is connected to a first middle portion 36c of the main oil passage 36. A check valve 40 is provided in the bypass oil passage 37. The check valve 40 allows the hydraulic oil to flow from the upstream side to the downstream side of the bypass oil passage 37 and regulates the flow of the hydraulic oil from the downstream side to the upstream side of the bypass oil passage 37.

[0029] The downstream end 36b of the main oil passage 36 is connected to communicate with the inside of the cylinder body 11 at the base end side of the cylinder body 11 of the lock cylinder 9 (one axial side of the piston 12). The downstream end 36b of the main oil passage 36 is located closer to the base end than the piston 12 when the contraction operation of the lock cylinder 9 is completed (the state shown in FIG. 3). As a result, the downstream end 36b of the main oil passage 36 always communicates with the hydraulic oil chamber 14 regardless of the extension / contraction state of the lock cylinder 9.

[0030] The downstream end 38b of the communicating oil passage 38 is connected to the dump cylinder 23 so as to always communicate with the hydraulic oil chamber 23a of the dump cylinder 23. The upstream end 38a of the communicating oil passage 38 is connected to the cylinder body 11 of the lock cylinder 9 on the tip side (left side in FIG. 3) of the downstream end 36b of the main oil passage 36 so as to communicate with the inside of the cylinder body 11. The upstream end 38a of the communicating oil passage 38 is located so as to be blocked by the outer circumferential surface of the piston 12 when the contraction operation of the lock cylinder 9 is completed, and is located on the base end side of the piston 12 when the extension operation of the lock cylinder 9 is completed (see FIG. 6).

[0031] Therefore, the upstream end 38a of the communicating oil passage 38 does not communicate with the hydraulic oil chamber 14 of the lock cylinder 9 during the extension and contraction operations of the lock cylinder 9, and communicates with the hydraulic oil chamber 14 of the lock cylinder 9 when the extension operation of the lock cylinder 9 is completed. As a result, the communicating oil passage 38 communicates between the hydraulic oil chamber 14 of the lock cylinder 9 and the hydraulic oil chamber 23a of the dump cylinder 23 when the extension operation of the lock cylinder 9 is completed.

[0032] The branch oil passage 39 branches off from the intermediate portion 38c of the communication oil passage 38 and is connected to a second intermediate portion 36d of the main oil passage 36. The second intermediate portion 36d is located downstream of the first intermediate portion 36c. A check valve 41 is provided in the branch oil passage 39. The check valve 41 allows the hydraulic oil to flow from the downstream side to the upstream side of the branch oil passage 39 and regulates the hydraulic oil to flow from the upstream side to the downstream side of the branch oil passage 39. The check valve 41 is provided integrally with the lock cylinder 9. The details will be described later.

[0033] [Lock cylinder configuration] FIG. 4 is a schematic cross-sectional view showing the internal configuration of the lock cylinder 9. FIG. 4 shows the state in which the lock cylinder 9 has finished contracting. Inside the cylinder body 11 of the lock cylinder 9, a spring 18 is attached to the rod 13 on the tip side of the piston 12. The spring 18 is made of a compression coil spring, and biases the piston 12 toward the base end side of the cylinder body 11. The biasing force of the spring 18 is smaller than the hydraulic pressure when the hydraulic oil filled in the hydraulic oil chamber 14 presses the piston 12. As a result, when the hydraulic oil is discharged from the hydraulic oil chamber 14, the lock cylinder 9 is contracted by the biasing force of the spring 18. Therefore, the biasing force of the spring 18 indirectly rotates the hook 8 to the engagement position.

[0034] A communication hole 19 is formed in the piston 12 and the rod 13, communicating one axial side and the other axial side of the piston 12. One end of the communication hole 19 opens at the end face of the piston 12 on the hydraulic oil chamber 14 side. The other end of the communication hole 19 opens at the outer circumferential surface of the rod 13. Hydraulic oil in the hydraulic oil chamber 14 on the one axial side of the piston 12 passes through the communication hole 19 and flows into the other axial side of the piston 12. As a result, the spring 18 is immersed in the hydraulic oil, which makes it possible to prevent the spring 18 from rusting.

[0035] The opening area of ​​the one end of the communication hole 19 is smaller than the cross-sectional area of ​​the end of the rod 13 on the piston 12 side. Due to this area difference, the pressure-receiving area of ​​the hydraulic oil at the end face on one axial side (the hydraulic oil chamber 14 side) of the piston 12 is larger than the pressure-receiving area of ​​the hydraulic oil at the end face on the other axial side of the piston 12. Therefore, when the lock cylinder 9 is extended from the state shown in Fig. 4, the hydraulic oil supplied to the hydraulic oil chamber 14 also flows into the other axial side of the piston 12 through the communication hole 19, but the difference in the pressure-receiving area of ​​the piston 12 allows the lock cylinder 9 to be extended.

[0036] Incidentally, the upstream end 38a of the communicating oil passage 38 (in FIG. 4, the inner end of a second oil hole 16 described later) is blocked by the outer circumferential surface of the piston 12 in the state (FIG. 4) in which the contraction operation of the lock cylinder 9 has been completed as described above. Therefore, even if the hydraulic oil in the hydraulic oil chamber 14 flows into the other axial side of the piston 12 through the communicating hole 19 when the lock cylinder 9 is extended from the state shown in FIG. 4, the hydraulic oil that has flowed in can be prevented from flowing out into the communicating oil passage 38 (second oil hole 16). This makes it possible to prevent the difference in the pressure-receiving area of ​​the piston 12 from being lost due to the outflow of hydraulic oil into the communicating oil passage 38, so that the lock cylinder 9 can be reliably extended.

[0037] 3 and 4, a first oil hole 15, a second oil hole 16, and a third oil hole 17 are formed in a wall portion 11a on the outer circumferential side of the cylinder body 11. The first oil hole 15 constitutes the downstream portion (part) of the main oil passage 36. The inner end (lower end in FIG. 4) of the first oil hole 15 is the downstream end 36b of the main oil passage 36, and communicates with the inside of the cylinder body 11 as described above. The outer end (upper end in FIG. 4) of the first oil hole 15 is the first connection port 15a that opens on the outer surface of the wall portion 11a of the cylinder body 11. A hydraulic pipe or the like that constitutes the upstream portion (other portion) of the main oil passage 36 is connected to the first connection port 15a.

[0038] The second oil hole 16 constitutes the upstream portion (part) of the communicating oil passage 38. The inner end of the second oil hole 16 is the upstream end 38a of the communicating oil passage 38, and communicates with the inside of the cylinder body 11 as described above. The outer end of the second oil hole 16 is the second connection port 16a that opens on the outer surface of the wall portion 11a of the cylinder body 11. A hydraulic pipe or the like that constitutes the downstream portion (other portion) of the communicating oil passage 38 is connected to the second connection port 16a.

[0039] The third oil hole 17 branches off from a midway portion of the second oil hole 16 and is connected to a midway portion of the first oil hole 15. The midway portion of the second oil hole 16 is a midway portion 38c of the communicating oil passage 38, and the midway portion of the first oil hole 15 is a second midway portion 36d of the main oil passage 36. As a result, the third oil hole 17 constitutes the entire branch oil passage 39.

[0040] The check valve 41 is provided in the middle of the third oil hole 17. The check valve 41 is, for example, a ball check valve, and has a ball 41a and a spring 41b that biases the ball 41a. The ball 41a is pressed in one direction (leftward in FIG. 4) toward the third oil hole 17 by the biasing force of the spring 41b, thereby closing the third oil hole 17. This restricts the flow of hydraulic oil from the first oil hole 15 to the second oil hole 16 in the third oil hole 17.

[0041] The hydraulic pressure of the hydraulic oil on the second oil hole 16 side of the third oil hole 17 acts on the ball 41a, causing the ball 41a to move in the other direction of the third oil hole 17 (to the right in FIG. 4) against the biasing force of the spring 41b. This releases the blockage of the third oil hole 17 by the ball 41a, and allows the hydraulic oil to flow from the second oil hole 16 to the first oil hole 15 in the third oil hole 17.

[0042] [Hydraulic circuit when driving] When the dump truck 1 is traveling, as shown in Fig. 3, the switching valve 35 is in a neutral position, and the main oil passage 36 is not connected to either the discharge oil passage 33 or the return oil passage 34. The dump cylinder 23 and the lock cylinder 9 are both in a state where they have finished contracting. In other words, the cargo box 3 is in a landed state, and the hook 8 of the lift-up prevention device 6 is in an engaged position. If vibrations occur while the dump truck 1 is traveling, the cargo box 3 will tend to lift up relative to the vehicle body 2. However, since the cargo box 3 is held in a landed state by the lift-up prevention device 6, it is possible to prevent the cargo box 3 from lifting up relative to the vehicle body 2.

[0043] [Hydraulic circuit when tilting the cargo box] Fig. 5 is a hydraulic circuit diagram explaining the flow of hydraulic oil when the cargo box 3 is tilted. When the worker operates a switch to tilt the cargo box 3 while the dump truck 1 is stopped (see Fig. 1), the switching valve 35 switches from the neutral position to the first position, as shown in Fig. 5. When the hydraulic pump 32 is driven in this state, the hydraulic oil discharged from the hydraulic pump 32 to the discharge oil passage 33 cannot pass through the first position of the switching valve 35, so it passes through the bypass oil passage 37 and flows into the main oil passage 36.

[0044] The hydraulic oil that flows into the main oil passage 36 flows into the hydraulic oil chamber 14 of the lock cylinder 9. At that time, some of the hydraulic oil in the main oil passage 36 also flows into the branch oil passage 39 from the second intermediate portion 36d, but the flow downstream is regulated by the check valve 41. For this reason, the hydraulic oil in the main oil passage 36 is not supplied to the hydraulic oil chamber 23a of the dump cylinder 23 via the branch oil passage 39.

[0045] When hydraulic oil is supplied to the hydraulic oil chamber 14 of the lock cylinder 9, the piston 12 moves toward the tip side of the cylinder body 11 against the biasing force of the spring 18. As a result, the lock cylinder 9 starts to extend, and the hook 8 starts to rotate from the engaged position toward the released position. During the extension of the lock cylinder 9, the piston 12 moves closer to the base end side of the cylinder body 11 than the upstream end 38a of the communicating oil passage 38, so that the hydraulic oil in the hydraulic oil chamber 14 of the lock cylinder 9 does not flow into the communicating oil passage 38. Therefore, during the extension of the lock cylinder 9, the hydraulic oil in the hydraulic oil chamber 14 is not supplied to the hydraulic oil chamber 23a of the dump cylinder 23 via the communicating oil passage 38.

[0046] Fig. 6 is a hydraulic circuit diagram showing a state in which the extension operation of the lock cylinder 9 has been completed. As shown in Fig. 6, when the extension operation of the lock cylinder 9 has been completed, the hook 8 is in the release position and the engagement with the lock pin 7 is released. In addition, since the piston 12 is located closer to the tip end side of the cylinder body 11 than the upstream end 38a of the communication oil passage 38, the communication oil passage 38 is communicated with the hydraulic oil chamber 14 of the lock cylinder 9. As a result, the hydraulic oil in the hydraulic oil chamber 14 is supplied to the hydraulic oil chamber 23a of the dump cylinder 23 through the communication oil passage 38.

[0047] When hydraulic oil is supplied to the hydraulic oil chamber 23a of the dump cylinder 23, the dump cylinder 23 extends as shown in Fig. 7, and the cargo box 3 tilts (see Fig. 2). During the extension of the dump cylinder 23, hydraulic oil is supplied to the hydraulic oil chamber 14 of the lock cylinder 9 by the hydraulic pump 32, so that the hydraulic pressure of the hydraulic oil filled in the hydraulic oil chamber 14 continues to act on the piston 12 of the lock cylinder 9. As a result, the lock cylinder 9 is held in the state where the extension operation has ended, and the hook 8 is held in the release position.

[0048] [Hydraulic circuit when the box is toppled] Fig. 8 is a hydraulic circuit diagram explaining the flow of hydraulic oil when the container 3 is tilted (see Fig. 2). When the worker operates the switch to tilt the container 3 while the container 3 is tilted (see Fig. 2), the switching valve 35 switches from the neutral position to the second position as shown in Fig. 8. This allows the return oil passage 34 and the main oil passage 36 to communicate with each other.

[0049] When the return oil passage 34 and the main oil passage 36 are connected, the hydraulic pressure of the hydraulic oil in each of the oil passages 36, 38, 39 downstream of the switching valve 35 is released. As a result, the dump cylinder 23 in the extended state starts to contract due to the weight of the cargo box 3. As the dump cylinder 23 contracts, the hydraulic oil in the hydraulic oil chamber 23a is discharged to the connecting oil passage 38.

[0050] A portion of the hydraulic oil discharged into the communicating oil passage 38 flows from the intermediate portion 38c of the communicating oil passage 38 into the branch oil passage 39, passes through the check valve 41, and flows into the main oil passage 36. The rest of the hydraulic oil discharged into the communicating oil passage 38 flows from the upstream end 38a of the communicating oil passage 38 through the hydraulic oil chamber 14 of the lock cylinder 9 into the main oil passage 36, and merges with some of the hydraulic oil. The hydraulic oil that has flowed into the main oil passage 36 in this manner passes through the second position of the switching valve 35 and the return oil passage 34, and returns to the oil tank 31.

[0051] During the contraction operation of the dump cylinder 23, hydraulic oil is supplied from the hydraulic oil chamber 23a of the dump cylinder 23 to the hydraulic oil chamber 14 of the lock cylinder 9 as described above, so the hydraulic pressure of the hydraulic oil filled in the hydraulic oil chamber 14 continues to act on the piston 12 of the lock cylinder 9. As a result, the lock cylinder 9 is held in the state where the extension operation has ended, so the hook 8 is held in the released position.

[0052] Fig. 9 is a hydraulic circuit diagram showing a state where the contraction operation of the dump cylinder 23 has been completed. As shown in Fig. 9, when the contraction operation of the dump cylinder 23 is completed and the cargo box 3 is in a floor-mounted state (see Fig. 2), hydraulic oil is no longer supplied from the hydraulic oil chamber 23a of the dump cylinder 23 to the hydraulic oil chamber 14 of the lock cylinder 9. As a result, the hydraulic pressure of the hydraulic oil in the hydraulic oil chamber 14 is released.

[0053] When the hydraulic pressure of the hydraulic oil in the hydraulic oil chamber 14 is released, the piston 12 of the lock cylinder 9 moves toward the base end of the cylinder body 11 due to the biasing force of the spring 18. This causes the lock cylinder 9 to start contracting, and the hook 8 starts to rotate from the release position toward the engagement position. As the lock cylinder 9 contracts, the hydraulic oil in the hydraulic oil chamber 14 passes through the main oil passage 36, the second position of the switching valve 35, and the return oil passage 34 and returns to the oil tank 31. As shown in Figure 10, when the lock cylinder 9 finishes contracting, the hook 8 reaches the engagement position and engages with the lock pin 7 on the cargo box 3 side.

[0054] [Effects] According to the dump truck 1 of this embodiment, the check valve 41 that regulates the flow of hydraulic oil from the upstream side to the downstream side in the branch oil passage 39 branching off from the communication oil passage 38 is provided integrally with the lock cylinder 9, so that by attaching the lock cylinder 9 integrated with the check valve 41 to the hydraulic circuit, the work of separately attaching the check valve 41 is not required. This makes it possible to reduce the number of steps required for assembling the dump truck 1.

[0055] Further, a third oil hole 17 constituting a branch oil passage 39 is formed in the wall portion 11a of the cylinder body 11 of the lock cylinder 9, and a check valve 41 is provided in the third oil hole 17. As a result, the branch oil passage 39 is integrally formed in the lock cylinder 9, so that by attaching the lock cylinder 9 to the hydraulic circuit, the work of separately providing the branch oil passage 39 in the hydraulic circuit is also unnecessary. As a result, the number of steps in assembling the dump truck 1 can be further reduced.

[0056] Furthermore, since a spring 18 that biases the piston 12 toward the base end side of the cylinder body 11 is provided inside the cylinder body 11 of the lock cylinder 9, the hook 8 can be indirectly rotated to the engagement position by the biasing force of the spring 18. This eliminates the need to separately attach the spring 18 to the hook 8 for rotating the hook 8 to the engagement position. As a result, the number of steps in assembling the dump truck 1 can be further reduced.

[0057] [others] It should be noted that the embodiment disclosed herein is illustrative in all respects and should not be considered as limiting. The scope of the present invention is not as described above, but is indicated by the claims, and is intended to include all modifications within the scope of the claims and meaning equivalent thereto. For example, the lock cylinder 9 of this embodiment is integrally provided with the branch oil passage 39 and the check valve 41, but it is sufficient that at least the check valve 41 is integrally provided. Also, only a part of the branch oil passage 39 may be formed in the lock cylinder 9.

[0058] In this embodiment, the spring 18 built into the lock cylinder 9 is provided closer to the tip end of the cylinder body 11 than the piston 12, but it may be provided closer to the base end (hydraulic oil chamber 14) of the cylinder body 11 than the piston 12. In that case, the spring 18 may be a tension coil spring that biases the piston 12 toward the base end of the cylinder body 11.

[0059] In addition, the spring 18 in this embodiment biases the piston 12 toward the base end side of the cylinder body 11 in order to bias the piston 12 toward one side in the axial direction, but the piston 12 may be biased toward the tip end side of the cylinder body 11. In that case, the spring 18 may be a compression coil spring provided closer to the base end side of the cylinder body 11 than the piston 12, or a tension coil spring provided closer to the tip end side of the cylinder body 11 than the piston 12. In this case, when the spring 18 biases the piston 12 toward the tip end side of the cylinder body 11, the hydraulic oil chamber 14 of the lock cylinder 9 may be formed closer to the tip end side of the cylinder body 11 than the piston 12. In addition, the communication oil passage 38 may communicate the hydraulic oil chamber 14 of the lock cylinder 9 with the hydraulic oil chamber 23a of the dump cylinder 23 when the contraction operation of the lock cylinder 9 is completed. Furthermore, since the biasing force of the spring 18 causes the lock cylinder 9 to extend, the shape of the hook 8 and the position of the lock pin 7 may be changed so that the position to which the hook 8 is rotated by the extension operation becomes the engagement position.

[0060] Furthermore, the spring 18 in this embodiment is built into the lock cylinder 9, but may be provided separately from the lock cylinder 9. Furthermore, the upstream end of the branch oil passage 39 in this embodiment is connected to the second intermediate portion 36d of the main oil passage 36, but may be connected so as to always communicate with the hydraulic oil chamber 14 of the lock cylinder 9, as in the above Patent Document 1. Furthermore, the hook 8 in this embodiment is engaged with the lock pin 7 fixed to the cargo box 3 at the engagement position, but may be directly engaged with the cargo box 3. [Explanation of symbols]

[0061] 1. Dump truck 2. Body 3 packing boxes 8. Hooks 9 Lock cylinder 11 Cylinder body 11a Wall 12 Piston 14 Hydraulic oil chamber (second oil chamber) 15 1st oil hole 16 2nd oil hole 17 3rd oil hole 18 Spring 23 Dump cylinder 23a Hydraulic oil chamber (first oil chamber) 36 Main Oil Line 38 Communication oil passage 39 Branch oil passage 41 Check valve

Claims

1. A cargo box tiltably provided with respect to the vehicle body; a dump cylinder having a first oil chamber through which hydraulic oil is supplied and discharged, and tilting the cargo box; a hook that is rotatably provided with respect to the vehicle body between an engagement position where the hook engages with the cargo box side and a release position where the hook is released from the cargo box side; a lock cylinder having a second oil chamber into which hydraulic oil is supplied and discharged, the lock cylinder being configured to rotate the hook to the release position by being extended when hydraulic oil is supplied to the second oil chamber, and to rotate the hook to the engagement position by being contracted when hydraulic oil is discharged from the second oil chamber; A main oil passage connected to the second oil chamber; a communication oil passage that communicates the first oil chamber with the second oil chamber when the extension operation of the lock cylinder is completed; a branch oil passage branching from the communication oil passage for returning a portion of the hydraulic oil discharged from the first oil chamber to the communication oil passage to the main oil passage; A check valve is provided in the branch oil passage to allow the hydraulic oil to flow from the communicating oil passage side to the main oil passage side and to regulate the hydraulic oil to flow from the main oil passage side to the communicating oil passage side, The check valve is provided integrally with the lock cylinder, The lock cylinder is A cylindrical cylinder body, a piston provided inside the cylinder body so as to be capable of reciprocating in an axial direction; the second oil chamber formed inside the cylinder body on one axial side of the piston; a rod having one end fixed to the other axial side of the piston; a communication hole that communicates the one axial side and the other axial side of the piston inside the cylinder body, the other axial side of the piston being formed inside the rod and opening at an outer circumferential surface of the rod, a spring for urging the piston to one axial direction is provided inside the cylinder body on the other axial direction side of the piston.

2. The wall of the cylinder body is provided with: A first oil hole that constitutes a part of the main oil passage; A second oil hole that constitutes a part of the communication oil passage; a third oil hole that branches off from a middle portion of the second oil hole, is connected to a middle portion of the first oil hole, and constitutes the branched oil passage, The dump truck according to claim 1 , wherein the check valve is provided in the third oil hole.

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