Material handling vehicles

Abstract

To provide a cargo handling vehicle equipped with a configuration that can reliably prevent excessive rotation of the cargo bed. [Solution] The dumping device that rotates the cargo bed comprises a cylinder 11 that pushes up and rotates the cargo bed, a hydraulic circuit 13 that hydraulically drives the cylinder 11, and a safety device 14 that restricts the hydraulic drive of the cylinder 11 to a safe range. The safety device 14 comprises a safety switching valve 50 that restricts the supply of hydraulic fluid from the hydraulic circuit 13 to the cylinder 11, a pneumatic knock-off valve 51 that switches the safety switching valve 50, and a pneumatic circuit 52 that switches the safety switching valve 50 when the pneumatic knock-off valve 51 is activated. The pneumatic knock-off valve 51 is activated in response to the upward tilting of the cylinder 11, thereby switching the safety switching valve 50 to the safe position and restricting the supply of hydraulic fluid to the cylinder 11.

Description

Technical Field

[0001] The present invention relates to a cargo handling vehicle. More specifically, in a cargo handling vehicle having a structure for unloading the load carried on a loading platform by tilting the loading platform mounted on a vehicle body such as a dump tractor or a dump trailer, the present invention relates to a safety technology for restricting the tilting of the loading platform within a safe range.

Background Art

[0002] For example, a dump trailer is formed by detachably connecting a tractor, which is a towing vehicle, and a trailer, which is a towed vehicle towed by this tractor. The loading platform is provided on the vehicle body of the trailer so as to be tiltable backward, and is equipped with a dump device for pushing up and tilting this loading platform.

[0003] Generally, the above dump device includes a cylinder for tilting the loading platform and a hydraulic circuit for hydraulically driving this cylinder. This hydraulic circuit mainly includes an oil tank, a hydraulic pump, and a switching valve for controlling the flow of hydraulic oil supplied to the cylinder.

[0004] And, the above hydraulic circuit is driven by the power taken out from the traveling engine by the power take-off device when an operator turns on the operation switch of the power take-off device (PTO) from the cab of the tractor. When the operator operates the dump lever to "raise", the above switching valve switches to the "raise" position, and when the operator steps on the accelerator pedal, the above hydraulic pump is driven to suck in and discharge hydraulic oil from the above oil tank. The discharged hydraulic oil is directionally controlled by the above switching valve and supplied to the above cylinder. As a result, the piston rod of the cylinder extends to push up and tilt the above loading platform, and the load in the loading platform slides down (Patent Document 1).

[0005] Conversely, when lowering the above loading platform from the tilted state to the horizontal state, when the operator operates the above dump lever to "lower", the above switching valve switches to the "lower" position, and while the above loading platform descends by its own weight, the piston rod of the cylinder contracts and extends, and the hydraulic oil returns to the oil tank through the switching valve.

[0006] Furthermore, if the cylinder extends excessively, a safety device is activated to bypass the hydraulic fluid flowing through the cylinder and return it to the oil tank, thereby preventing excessive tilting of the loading platform.

[0007] Specifically, the safety device consists of a hydraulic knock-off valve installed in the hydraulic circuit. When the cylinder extends and tilts to a certain angle, the cylinder comes into contact with the operating projection of the knock-off valve, pushing it. This causes the knock-off valve to switch over, and the entire amount of hydraulic fluid flowing to the cylinder flows through the knock-off valve to the bypass oil passage. The hydraulic fluid that flows into this bypass oil passage is returned to the oil tank and does not flow back into the cylinder, thus preventing further extension of the cylinder. [Prior art documents] [Patent Documents]

[0008] [Patent Document 1] Japanese Unexamined Patent Publication No. 58-133930 [Overview of the Initiative] [Problems that the invention aims to solve]

[0009] However, the above-described safety device configuration had the following problems.

[0010] In other words, the hydraulic knock-off valve used as a safety device primarily functions as a sensor valve that operates via a switch, and structurally, it does not have the capacity to bypass and recirculate a large amount of hydraulic fluid compared to a typical switching valve that forms a hydraulic circuit.

[0011] On the other hand, individual differences among operators handling dump tractors and operational errors can sometimes cause the cylinder to extend excessively. For example, if an operator presses the accelerator pedal too hard in an attempt to quickly push up and rotate the cargo bed, a large amount of hydraulic fluid from the oil tank will be supplied to the cylinder, causing the piston rod to extend rapidly. Even if the knock-off valve, which acts as a safety device, is activated at this time, the amount of hydraulic fluid supplied may exceed the processing capacity of the knock-off valve. As a result, the hydraulic fluid that cannot be bypassed and recirculated by the knock-off valve is further supplied to the cylinder, causing the cargo bed to rotate beyond the predetermined safety angle. In the worst case, this could cause the dump trailer to lose balance and tip over.

[0012] The present invention has been made in view of the aforementioned conventional problems, and its objective is to provide a cargo handling vehicle equipped with a configuration that can reliably prevent excessive rotation of the cargo bed. [Means for solving the problem]

[0013] To achieve the above objective, the cargo handling vehicle of the present invention comprises a rotating device rotatably mounted on the vehicle body and a rotating mechanism for rotating the rotating device, the rotating mechanism comprising a cylinder for pushing up and rotating the rotating device, a hydraulic circuit for hydraulically driving the cylinder, and a safety device for restricting the hydraulic drive of the cylinder to a safe range, the safety device comprising a safety switching valve for restricting the supply of hydraulic fluid from the hydraulic circuit to the cylinder, a pneumatic knock-off valve for switching control of the safety switching valve, and a pneumatic circuit for switching the safety switching valve when the pneumatic knock-off valve is activated, the pneumatic knock-off valve is configured to activate in accordance with the tilt angle of the cylinder accompanying the upward pushing operation of the cylinder, thereby switching the safety switching valve to a safe position and restricting the supply of hydraulic fluid to the cylinder.

[0014] A preferred embodiment employs the following configuration. (1) The hydraulic circuit comprises an oil tank, a hydraulic pump, a main switching valve that controls the supply of hydraulic fluid to the cylinder, and a safety switching valve. The pneumatic circuit is configured to supply working air from an air tank to a pneumatic switching valve that hydraulically operates the safety switching valve by the switching operation of the pneumatic knock-off valve.

[0015] (2) The above-mentioned vehicle is configured such that a towing vehicle and a towed vehicle towed by the towing vehicle are detachably connected, and the towed vehicle is provided with the rotating device, the cylinder of the rotating mechanism and the pneumatic knock-off valve and pneumatic circuit of the safety device, and the towing vehicle is provided with the hydraulic circuit of the dumping device, and the hydraulic circuit and cylinder of the dumping device are connected by a detachable dedicated oil pipe.

[0016] Here, the rotating device may be a cargo bed. The rotating device may be installed so as not to be detached from the vehicle, or it may be installed so as to be detachable from the vehicle as needed. It is preferable that the cargo handling vehicle is a vehicle equipped with a structure that allows the cargo loaded on the cargo bed to be unloaded by rotating the cargo bed, which is the rotating device. Note that the rotation of the rotating device includes tilting. Specifically, it is preferable that the cargo handling vehicle is a vehicle equipped with a structure that allows the cargo loaded on the cargo bed to be unloaded by tilting the cargo bed.

[0017] Furthermore, it is preferable that the rotating mechanism is a dumping device that tilts the rotating device.

[0018] Furthermore, it is preferable that the pneumatic knock-off valve detects the inclination angle of the cylinder by being pressed against the cylinder via the rotating curved surface of the cam.

[0019] Furthermore, it is preferable that the cam is provided with axially rotatable rollers in the portions that come into contact with the pneumatic knock-off valve and the cylinder, respectively. [Effects of the Invention]

[0020] According to the cargo handling vehicle of the present invention, the rotating mechanism for rotating the rotating device comprises the rotating device rotatably mounted on the vehicle body and the rotating mechanism for rotating the rotating device, the rotating mechanism comprises a cylinder that pushes up and rotates the rotating device, a hydraulic circuit that hydraulically drives the cylinder, and a safety device that restricts the hydraulic drive of the cylinder to a safe range, the safety device comprises a safety switching valve that restricts the supply of hydraulic fluid from the hydraulic circuit to the cylinder, a pneumatic knock-off valve that controls the switching of the safety switching valve, and a pneumatic circuit that switches the safety switching valve when the pneumatic knock-off valve is activated, the pneumatic knock-off valve is activated in accordance with the tilt angle of the cylinder accompanying the upward pushing operation of the cylinder, thereby switching the safety switching valve to a safe position and restricting the supply of hydraulic fluid to the cylinder, so that the unique effects described below can be obtained and a cargo handling vehicle with a configuration that can reliably prevent excessive rotation of the cargo bed can be provided.

[0021] (1) The dumping device that rotates the rotating mechanism is equipped with a safety device that restricts the hydraulic drive of the cylinder to a safe range, and this safety device comprises a safety switching valve that restricts the supply of hydraulic fluid to the cylinder of the hydraulic circuit that hydraulically drives the cylinder, and a pneumatic knock-off valve that switches the safety switching valve, and this pneumatic knock-off valve is configured to activate in accordance with the tilt angle of the cylinder due to the upward pushing operation of the cylinder, thereby switching the safety switching valve to the safe position and restricting the supply of hydraulic fluid to the cylinder, so that excessive tilting of the loading platform can be reliably prevented.

[0022] That is, the hydraulic knock-off valve as a safety device in the conventional rotation mechanism is provided in a hydraulic circuit that hydraulically drives the cylinder, and in addition to its function as a sensor component that switches in an emergency, it also has the function of bypassing and refluxing the hydraulic oil supplied to the cylinder to the oil tank. Structurally, it cannot pass a very large amount of hydraulic oil. If the supply amount of the hydraulic oil exceeds the allowable throughput capacity of the knock-off valve, it impairs the function as a safety device for preventing excessive rotation of the cargo bed, leading to a situation where excessive tilting of the cargo bed cannot be prevented.

[0023] In contrast, the safety device of the present invention includes a dedicated safety switching valve that regulates the supply of hydraulic oil to the cylinder, and a pneumatic knock-off valve as a switch sensor that switches and controls the safety switching valve in an emergency. When this pneumatic knock-off valve is activated corresponding to an excessive inclination angle of the cylinder accompanying the lifting operation of the cylinder, the safety switching valve switches to the safety position, and the entire amount of hydraulic oil supplied to the cylinder can be bypassed and refluxed to the oil tank, reliably regulating excessive rotation of the cargo bed within a safe range.

[0024] (2) In a dump trailer in which a tractor as a towing vehicle and a trailer towed by this tractor are detachably connected, by adopting a configuration in which the pneumatic knock-off valve and the pneumatic circuit of the safety device are provided in the trailer, the pneumatic circuit configuration of the safety device can be completed only in the trailer, reducing the connection of dedicated piping between the tractor and the trailer, and achieving labor saving such as reducing the work burden.

Brief Description of the Drawings

[0025] [[ID=Fourteen]] [Figure 1] It is a side view schematically showing the schematic configuration of a dump trailer 1 which is an embodiment according to the present invention. [Figure 2]Figure 2(a) is an enlarged side view showing the arrangement of the cylinder 11 and the knock-off valve 51 within the dashed-dotted circle in Figure 1 of the dump trailer 1. Figure 2(b) shows the non-contact state of the cylinder 11 and the knock-off valve 51, while Figure 2(b) shows the contact state of the cylinder 11 and the knock-off valve 51. [Figure 3] This is a hydraulic circuit diagram for the dump trailer 1. [Figure 4] This figure shows a second embodiment in which a link 55 is used as the contact structure between the cylinder 11 and the pneumatic knock-off valve 51. Figure 4(a) shows the state just before the cylinder 11 reaches the dangerous tilt angle, and Figure 4(b) shows the state when the cylinder 11 is tilted beyond the dangerous tilt angle. [Figure 5] This figure shows a second embodiment in which a link 55 is used as the contact structure between the cylinder 11 and the pneumatic knock-off valve 51. Figure 5(a) shows the state just before the cylinder 11 reaches the dangerous tilt angle, and Figure 5(b) shows the state when the cylinder 11 is tilted beyond the dangerous tilt angle. [Figure 6] This figure shows a second embodiment in which a link 55 is used as the contact structure between the cylinder 11 and the pneumatic knock-off valve 51. Figure 6(a) shows the state just before the cylinder 11 reaches the dangerous tilt angle, and Figure 6(b) shows the state when the cylinder 11 is tilted beyond the dangerous tilt angle. [Modes for carrying out the invention]

[0026] [First Embodiment] Hereinafter, a first embodiment of the present invention will be described in detail with reference to the drawings. Note that the same reference numerals throughout the drawings indicate the same component or element.

[0027] A dump trailer according to the present invention is shown in Figures 1 to 3. As shown in Figure 1, this dump trailer 1 consists of a tractor 2, which is a towing vehicle, and a trailer 3, which is a towed vehicle towed by the tractor 2, connected together. The cargo loaded on the cargo bed 4 is unloaded by tilting and rotating the cargo bed 4, which is a rotating device of the trailer 3.

[0028] The tractor 2 described above has a driver's cab 6 at the front of the tractor body 5, and the trailer 3 described above is detachably connected to the rear by a coupling mechanism. The tractor body 5 is also equipped with a drive engine and a power take-off (PTO) 7 for the dumping device 10 described later.

[0029] The trailer 3 described above has a cargo bed 4 mounted on the trailer body 8 so as to be rotatable while tilting backward, and is equipped with a cylinder 11 of the dump device 10, which is a rotation mechanism for pushing up and rotating the cargo bed 4. Specifically, the rear lower end 4a of the cargo bed 4 is rotatably hinged to the trailer body 8 (not shown), and the base end 11a of the cylinder 11 is rotatably pivoted to the trailer body 8 (not shown), and the tip 12a of the piston rod 12 is pivotally supported to the front end 4b of the cargo bed 4.

[0030] The dumping device 10 described above is a rotating mechanism for rotating the cargo bed 4, and its main components are the cylinder 11, the hydraulic circuit 13 that hydraulically drives the cylinder 11, and the safety device 14 (Figure 3) that restricts the hydraulic drive of the cylinder 11 to a safe range.

[0031] Furthermore, since the tractor 2 and the trailer 3 are configured to be detachably connected, the trailer 3 is equipped with the cylinder 11 of the dumping device 10, the pneumatic knock-off valve 51 and pneumatic circuit 52 (Figure 3) of the safety device 14 (described later), and the tractor 2 is equipped with the hydraulic circuit 13 (Figure 3) of the dumping device 10. This detachable configuration of the dumping device 10 makes it easy to separate and connect the components of the dumping device 10 when separating and connecting the tractor 2 and the trailer 3.

[0032] In the illustrated embodiment, the cylinder 11 is a single-acting telescopic cylinder, and is equipped with a hydraulic fluid chamber 11b (Figure 3) at its base end. The piston rod 12 extends and retracts by supplying and discharging hydraulic fluid to and from this hydraulic fluid chamber 11b.

[0033] As shown in Figure 3, the hydraulic circuit 13 mainly comprises an oil tank 20, a hydraulic pump 21, a main switching valve 22, and a safety switching valve 50 of the safety device 14. A supply oil passage 23 is piped between the hydraulic pump 21 and the main switching valve 22, and a return oil passage 24 is piped between the oil tank 20 and the main switching valve 22. In addition, a main oil passage 25 is piped between the main switching valve 22 and the safety switching valve 50, and a main oil passage 26 is piped between the safety switching valve 50 and the cylinder 11. Furthermore, a return bypass oil passage 27 connected to the safety switching valve 50 is connected to the return oil passage 24.

[0034] In Figure 3, the VV line indicates the dividing point where the components of the dumping device 10, including the hydraulic circuit 13, are mounted on the tractor 2 and the trailer 3, respectively. The parts to the left of the VV line are mounted on the tractor 2, and the parts to the right are mounted on the trailer 3.

[0035] In the illustrated embodiment, the hydraulic circuit 13 and cylinder 11 of the dumping device 10 are connected by a detachable dedicated oil pipe, i.e., the main oil passage 25. For this purpose, the main oil passage 25 and the return bypass oil passage 27 are configured to be detachably connected at the connection points between the tractor 2 and the trailer 3 by a high-pressure side coupler 40 and a low-pressure side coupler 41, respectively.

[0036] The hydraulic pump 21 draws hydraulic fluid from the oil tank 20 and discharges it into the supply oil passage 23, and the hydraulic fluid flowing through this supply oil passage 23 is supplied to the main switching valve 22. The supply oil passage 23 is equipped with a check valve 28 to prevent the hydraulic fluid from flowing back towards the hydraulic pump 21. The return oil passage 24 is an oil passage through which hydraulic fluid returns from the main oil passage 25 via the main switching valve 22, and also returns hydraulic fluid from the supply oil passage 23 via the main switching valve 22 to the oil tank 20. A filter 29 and a check valve 30 are connected to this return oil passage 24 as shown in the figure.

[0037] The main switching valve 22 switches between a hydraulic fluid supply position that connects the supply oil passage 23 and the main oil passage 25, and a hydraulic fluid return position that connects the return oil passage 24 and the main oil passage 25.

[0038] The main switching valve 22 in the illustrated embodiment is a pneumatic switching valve with 3 ports and 3 positions, to which the supply oil passage 23, return oil passage 24, and main oil passage 25 are connected, respectively, and the switching operation is performed by switching the switching valve 31 by operating a lever by an operator.

[0039] When the main switching valve 22 is not operating, it is in the neutral position (the center position in Figure 3). In this neutral position, the main oil passage 25 does not communicate with either the supply oil passage 23 or the return oil passage 24, while the supply oil passage 23 and the return oil passage 24 communicate with each other.

[0040] When the operator switches the switching valve 31 by operating the lever, the main switching valve 22 switches from the neutral position to the hydraulic fluid supply position (the position on the right in Figure 3), the supply oil passage 23 communicates with the main oil passage 25, while the return oil passage 24 does not communicate with either oil passage 23 or 25. As a result, hydraulic fluid flows from the supply oil passage 23 to the main oil passage 25.

[0041] Furthermore, when the operator switches the switching valve 31 by operating the lever, the main switching valve 22 switches from the neutral position to the hydraulic fluid return position (the position on the left in Figure 3), the return oil passage 24 communicates with the main oil passage 25, and the supply oil passage 23 also communicates with the return oil passage 24. As a result, the hydraulic fluid from the supply oil passage 23 and the main oil passage 25 merge and flow into the return oil passage 24. This causes hydraulic fluid to flow from the main oil passage 25 towards the return oil passage 24.

[0042] The main oil passage 25 is connected to the main oil passage 26 via the safety switching valve 50 of the safety device 14, and this main oil passage 26 is connected to the hydraulic fluid chamber 11b of the cylinder 11. As will be described later, the safety switching valve 50 is in the non-operating position (left side position in Figure 3) under normal conditions, and the main oil passage 25 and the main oil passage 26 are in communication.

[0043] Relief valves 32 and 33 are provided in the main oil passages 25 and 26 to set the pressure applied to the cylinder 11. In addition, a check valve 34 is provided in the main oil passage 25, and a check valve 35 is provided in parallel with the check valve 34 and in the opposite direction.

[0044] The safety device 14 is for restricting the rotation of the cargo bed 4 to a safe range and comprises a safety switching valve 50 that restricts the supply of hydraulic fluid to the cylinder 11 of the hydraulic circuit 13, a pneumatic knock-off valve 51 that switches and activates the safety switching valve 50, and a pneumatic circuit 52 that switches the safety switching valve 50 when the pneumatic knock-off valve 51 is activated.

[0045] The safety switching valve 50 switches between a hydraulic fluid supply / return position that connects the main oil passage 25 and the main oil passage 26, and an emergency position (safety position) that does not connect the main oil passage 25 and the main oil passage 26, but connects the main oil passage 25 and the return bypass oil passage 27.

[0046] The safety switching valve 50 in the illustrated embodiment is a 4-port, 2-position pilot switching valve. When the pneumatic knock-off valve 51 is activated in an emergency, the working air supplied from the air tank 54 (Figure 1) of the trailer body 8 to the pneumatic switching valve 53 through the IN port of the pneumatic knock-off valve 51 is shut off, and the pneumatic circuit 52 is opened to the atmosphere through the OUT port, causing the pneumatic switching valve 53 to switch. As a result, pilot pressure oil (hydraulic oil) is supplied to the safety switching valve 50 from the main oil passage 25, and the safety switching valve 50 switches to the emergency position (safety position).

[0047] In its normal non-operating state, the safety switching valve 50 is in the hydraulic fluid supply / return position (left side position in Figure 3). In this position, the main oil passage 25 is in communication with the main oil passage 26, while the return bypass oil passage 27 is not in communication with the main oil passage 26.

[0048] On the other hand, when the pneumatic knock-off valve 51 is activated in an emergency, the pneumatic switching valve 53 switches the safety switching valve 50 from the hydraulic fluid supply / return position to the emergency position (safety position) (the position on the right in Figure 3), cutting off communication between the main oil passage 25 and the main oil passage 26, and the main oil passage 25 communicates with the return bypass oil passage 27. As a result, the supply of hydraulic fluid from the main oil passage 25 to the main oil passage 26 is cut off, and the entire amount of hydraulic fluid flows to the return bypass oil passage 27, and the hydraulic fluid that flows to the return bypass oil passage 27 returns to the oil tank 20 through the return oil passage 24.

[0049] Here, the emergency situation in which the pneumatic knock-off valve 51 is activated is when the cargo bed 4 mounted on the trailer 3 rotates excessively to the rear, creating a dangerous situation where the dump trailer 1 loses balance and overturns. In practical terms, this occurs when the piston rod 12 of the cylinder 11 extends to a certain tilt angle (dangerous tilt angle), and the pneumatic knock-off valve 51 is configured to sense this tilt and activate.

[0050] Specifically, as shown in Figure 2, the pneumatic knock-off valve 51 is positioned at the rear side of the cylinder 11, which is rotatably supported on the trailer body 8, in the direction of upward rotation of the cylinder 11. Under normal conditions, the operating projection 51a of the pneumatic knock-off valve 51 does not contact the cylinder 11 (state shown in Figure 2(a)). However, at a dangerous tilt angle of the cylinder 11, which occurs when the dump trailer 1 is in a dangerous condition where it may tip over, the cylinder 11 comes into contact with the operating projection 51a of the pneumatic knock-off valve 51, pressing it (state shown in Figure 2(b)). As a result, the pneumatic knock-off valve 51 is configured to sense this dangerous condition and activate in an emergency.

[0051] In other words, when the extension of the cylinder 11 causes the cylinder 11 to rotate excessively backward, as shown in Figure 2(b), the cylinder 11 comes into contact with the operating projection 51a of the pneumatic knock-off valve 51 and presses against this projection 51a. This activates the pneumatic knock-off valve 51, stopping the supply of working air from the air tank 54 to the pneumatic switching valve 53. As the working air supplied to the pneumatic circuit 52 is released to the atmosphere, the pneumatic switching valve 53 switches. This causes pilot pressure oil (hydraulic oil) to be supplied from the main oil passage 25 to the safety switching valve 50. The safety switching valve 50 switches from the normal non-operating state, i.e., the hydraulic oil supply / return position (left side in Figure 3), to the emergency position (safety position) (right side in Figure 3). This disconnects the main oil passage 25 from the main oil passage 26, and the main oil passage 25 connects to the return bypass oil passage 27. Then, the supply of hydraulic fluid from the main oil passage 25 to the main oil passage 26 is cut off, and the entire amount of hydraulic fluid flows into the return bypass oil passage 27, and then returns to the oil tank 20 through the return oil passage 24.

[0052] As a result, the hydraulic fluid supplied from the oil tank 20 to the main oil passage 25 does not flow into the main oil passage 26, but the entire amount of supplied hydraulic fluid is returned to the oil tank 20 via the return bypass oil passage 27. This prevents the cylinder 11 from extending any further, stopping excessive rotation beyond the safe range of the cargo bed 4, and reliably avoiding the danger of the dump trailer 1 losing balance and tipping over.

[0053] In this regard, other embodiments can also be used for the installation method of the pneumatic knock-off valve 51.

[0054] [Second Embodiment] In a second embodiment, as shown in Figures 4(a) and 4(b), it is preferable that a link 55 is interposed between the pneumatic knock-off valve 51 and the cylinder 11, which is equipped with a mechanism capable of pressing the operating projection 51a of the pneumatic knock-off valve 51 by rotational movement.

[0055] Here, we will briefly describe the pneumatic knock-off valve 51 and its surrounding mechanism in the second embodiment. The base end 11a of the cylinder 11 is pivotally supported via a pivot shaft 57 on a support frame 56 fixed to the trailer body 8. A pneumatic knock-off valve 51 is also installed on the outer surface of the support frame 56 with an operating projection 51a facing upwards toward the trailer body 8. In this embodiment, the pneumatic knock-off valve 51 has an operating projection 51a that protrudes upwards from its upper end, and the area around the projection 51a is covered with an elastic body 58. When the operating projection 51a is extended, it is in a non-operating state, and when the operating projection 51a is pushed downwards against the elastic force of the elastic body 58, it enters an emergency position.

[0056] Furthermore, the link 55 includes a link cover 59 fixed to the support frame 56 so as to cover the upper part of the pneumatic knock-off valve 51, and a cam 61 provided at the upper end of the link cover 59, which is pivotally supported on the link cover 59 via a support shaft 60 so as to be rotatable in a plane parallel to the operating axis of the operating projection 51a. The contact surface (cam surface) 62 of the cam 61 is in contact with the upper end of the operating projection 51a, while a rod-shaped rod 64 is provided protruding from the front surface 63 of the cam 61 toward the circumferential surface of the cylinder 11.

[0057] Figure 4(a) shows the state just before the cylinder 11 reaches the dangerous tilt angle, and Figure 4(b) shows the state when the cylinder 11 is tilted beyond the dangerous tilt angle. When the cylinder 11 reaches the dangerous tilt angle, the circumferential surface of the ricinder 11 comes into contact with the tip of the rod 64, pushing the rod 64 toward the rear of the vehicle. When pushed by the cylinder 11, the rod 64 rotates with the pivot shaft 60 as the pivot point, with its tip pointing upward as shown in Figure 4(b), and also rotates the cam 61.

[0058] As the cam 61 rotates, the contact surface 62, which is formed by a curved surface whose distance from the support shaft 60 gradually increases, rotates and presses against the operating projection 51a, switching the pneumatic knock-off valve 51 to the emergency position.

[0059] When the pneumatic knock-off valve 51 is switched to the emergency position, communication between the main oil passage 25 and the main oil passage 26 is severed, and the main oil passage 25 communicates with the return bypass oil passage 27. Then, the supply of hydraulic fluid from the main oil passage 25 to the main oil passage 26 is cut off, and the entire amount of hydraulic fluid flows into the return bypass oil passage 27, and further returns to the oil tank 20 through the return oil passage 24. In this way, the dangerous tilt angle of the cylinder 11 is resolved, and the cargo bed 4 collapses onto the trailer body 8 while the cylinder 11 is contracting, becoming horizontal. At this point, the elastic force of the elastic body 58 pushes the operating projection 51a in the direction of extension, and the pneumatic knock-off valve 51 returns to the non-operating state.

[0060] In this way, by creating a structure in which the operating projection 51a is pressed not directly by the circumferential surface of the cylinder 11, but via a link 55 equipped with a cam 61, the direction of the force applied between the contact surface 62 and the operating projection 51a can be made to be in the direction along the operating axis. In particular, by making it easier for the operating projection 51a to return to the non-operating state while pushing back the cam 61 due to the reaction force of the elastic body 58, malfunctions that prevent it from returning to the non-operating state can be prevented.

[0061] [Third Embodiment] Figure 5 shows a schematic diagram of the pneumatic knock-off valve 51 and its surrounding mechanism in the third embodiment. Figure 5(a) shows the cylinder 11 just before it reaches the dangerous tilt angle, and Figure 5(b) shows the cylinder 11 when it is tilted beyond the dangerous tilt angle.

[0062] The third embodiment is characterized in that, in the mechanism of the second embodiment, the tip of the rod 64 is provided to protrude from the cam 61 so as to be approximately perpendicular to or between the circumferential surface of the cylinder 11 at a critical inclination angle and slightly expand upward.

[0063] This makes it easier to rotate the rod 64 upward when pushing the rod 64 after the cylinder 11 has reached a dangerous tilt angle. It also prevents accidents such as accidentally pushing the rod 64 downward and bending it.

[0064] [Fourth Embodiment] Figure 6 shows a schematic diagram of the pneumatic knock-off valve 51 and its surrounding mechanism in the fourth embodiment. Figure 6(a) shows the cylinder 11 just before it reaches the dangerous tilt angle, and Figure 6(b) shows the cylinder 11 when it is tilted beyond the dangerous tilt angle.

[0065] The fourth embodiment is the mechanism of the third embodiment, wherein a roller 65 is rotatably attached to the tip of the rod 64. The roller 64 can come into contact with the cylinder 11 when it reaches a critical inclination angle. Furthermore, a roller 66 is mounted rotatably on the axial axis at a position corresponding to the contact surface 62 of the cam 61. The roller 66 allows the cam 61 to contact the operating projection 51a of the pneumatic knock-off valve 51 and smoothly press the operating projection 51a while rotating on the axial axis.

[0066] Here, it is preferable that the rollers 65 and 66 are made of resin. This is because being made of resin ensures reliable rotational operation through close contact between the rollers 65 and 66 and the object they come into contact with.

[0067] Furthermore, although the rollers 65 and 66 were described in this embodiment in relation to the mechanism of the third embodiment, the rollers 65 and 66 can also be applied to the mechanism of the second embodiment.

[0068] In the dump trailer 1 configured as described above, when the operator turns on the power take-off (PTO) 7 operation switch from the driver's cab 6 of the dump trailer 1, the hydraulic circuit 13 of the dump device 10 is driven by the power taken from the driving engine by the power take-off 7. When the operator "lifts" the dump lever, the switching valve 31 switches the main switching valve 22 from the neutral position (center position in Figure 3) to the hydraulic fluid supply position (left position in Figure 3). When the operator presses the accelerator pedal, the hydraulic pump 21 is driven, drawing in and discharging hydraulic fluid from the oil tank 20. This discharged hydraulic fluid is directed by the main switching valve 22 and supplied to the cylinder 11. As a result, the piston rod 12 of the cylinder 11 extends, pushing up the front of the cargo bed 4 and rotating it backward, causing the cargo inside the tilted cargo bed 4 to slide down.

[0069] When the operator "holds" the dump lever while the loading platform 4 is tilted, the switching valve 31 switches the main switching valve 22 to the neutral position, blocking the main oil passage 25 from communicating with either the supply oil passage 23 or the return oil passage 24, while the supply oil passage 23 and the return oil passage 24 communicate with each other, thereby maintaining the current tilted position of the loading platform 4.

[0070] When the unloading of the cargo from the cargo bed 4 is completed and the operator lowers the dump lever, the switching valve 31 switches the main switching valve 22 to the hydraulic fluid return position (right side in Figure 3), and the return oil passage 24 communicates with the main oil passage 25. As a result, the extended cylinder 11 begins to retract due to the weight of the cargo bed 4, and the piston rod 12 of the cylinder 11 retracts, causing the hydraulic fluid in the hydraulic fluid chamber 11b of the cylinder 11 to return to the oil tank 20 via the return oil passage 24 through the main oil passages 26 and 25 and the main switching valve 22. As a result, the cargo bed 4 collapses onto the trailer body 8 while the cylinder 11 retracts, becoming horizontal.

[0071] Furthermore, individual differences among workers or operational errors may cause the cylinder 11 to extend excessively. For example, if a worker hastily pushes up the cargo bed 4 and presses the accelerator pedal too hard, a large amount of hydraulic fluid from the oil tank 20 will be supplied to the hydraulic fluid chamber 11b of the cylinder 11, causing the piston rod 12 to extend rapidly and the cargo bed 4 to attempt to rotate excessively. In such a dangerous emergency, the safety device 14 will detect the emergency and activate, as described above. As a result, the cylinder 11 will not extend any further, the excessive rotation of the cargo bed 4 beyond its safe range will stop, and the danger of the dump trailer 1 losing balance and tipping over will be reliably avoided.

[0072] As detailed above, the dump trailer 1 of this embodiment provides the following unique advantages.

[0073] (a) The dumping device 10 that rotates the loading platform 4 is equipped with a safety device 14 that restricts the hydraulic drive of the cylinder 11 to within a safe range. This safety device 14 includes a safety switching valve 50 that restricts the supply of hydraulic fluid to the cylinder 11 from the hydraulic circuit 13 that hydraulically drives the cylinder 11, and a pneumatic knock-off valve 51 that switches the safety switching valve 50. The pneumatic knock-off valve 51 is activated in response to the tilt angle of the cylinder 11 caused by the pushing up of the loading platform 4, thereby switching the safety switching valve 50 to the safe position and restricting the supply of hydraulic fluid to the cylinder 11. This ensures that excessive rotation of the loading platform 4 can be reliably prevented.

[0074] In other words, the hydraulic knock-off valve, which serves as a safety device in conventional dump trucks, is installed in the hydraulic circuit 13 that hydraulically drives the cylinder 11. In addition to functioning as a sensor component that switches on in an emergency, it also has the function of bypassing the hydraulic fluid supplied to the cylinder 11 and returning it to the oil tank 20. However, due to its structure, it cannot pass a large amount of hydraulic fluid through it. If the amount of hydraulic fluid supplied exceeds the allowable flow capacity of the hydraulic knock-off valve, it impairs its function as a safety device to prevent excessive rotation of the cargo bed 4, resulting in a situation where excessive rotation of the cargo bed 4 cannot be prevented.

[0075] In contrast, the safety device 14 of this embodiment includes a dedicated safety switching valve 50 that restricts the supply of hydraulic fluid to the cylinder 11, and a pneumatic knock-off valve 51 that acts as a switch sensor to control the switching of the safety switching valve 50 in an emergency. When the pneumatic knock-off valve 51 is activated in response to an excessive tilt angle of the cylinder 11 due to the upward tilting of the cylinder 11, the safety switching valve 50 switches to the safety position, allowing the entire amount of hydraulic fluid supplied to the cylinder 11 to be bypassed and recirculated to the oil tank 20, thereby reliably restricting excessive rotation of the loading platform 4 to within a safe range.

[0076] (b) In a dump trailer 1 in which a tractor 2, which is a towing vehicle, and a trailer 3 towed by the tractor 2 are detachably connected, the trailer 3 is provided with the pneumatic knock-off valve 51 and pneumatic circuit 52 of the safety device 14. This configuration allows the circuit configuration of the pneumatic circuit 52 of the safety device 14 to be completed solely on the trailer 3, reducing the number of dedicated piping connections between the tractor 2 and the trailer 3 (only the main oil passage 25 and the return bypass oil passage 27 in the illustrated embodiment), thereby reducing the workload and saving labor.

[0077] The embodiments described above are merely preferred embodiments of the present invention, and the present invention is not limited to these embodiments; various design modifications are possible within their scope.

[0078] For example, regarding the specific structure of each component constituting the dump device 10, other structures having the same function as the illustrated embodiment can be adopted. For instance, the specific configuration of the safety device 14 is not limited to the illustrated embodiment, and other configurations having the same function can be adopted.

[0079] Furthermore, another example of a dumping device 10 that can be adopted is a link-type structure. The link-type structure has a dumping structure in the center of the bottom surface of the cargo bed 4, and the cargo bed 4 can be dumped by tilting motion in conjunction with the hoist cylinder and a combination of a lift arm, tension link, etc. In other words, when using the link-type structure, the entire link-type structure corresponds to the cylinder 11 in the present invention.

[0080] Therefore, when a link-type structure is adopted, the pneumatic knock-off valve 51 constituting the safety device 14 can be configured to switch the safety switching valve 50 according to the present invention to the safe position by contacting the circumferential surface of either the hoist cylinder, the lift arm, or the tension link when they reach a predetermined dangerous inclination angle.

[0081] Furthermore, the present invention is applicable not only to the dump trailer 1 as shown in the illustrated embodiment, but also to other cargo handling vehicles having the same function, such as dump trucks and arm roll trucks whose cargo beds can be detached as needed. [Explanation of Symbols]

[0082] 1 Dump trailer 2 tractors 3 Trailers 4. Cargo bed 5. Tractor body 6. Driver's cab 7 Power takeoff device (PTO) 8 Trailer body 10 Dumping device 11 cylinders 12 Piston Rods 13. Hydraulic Circuit 14 Safety equipment 20 oil tanks 21 Hydraulic pump 22 Main switching valve 23. Supply oil channels 24 Return oil channel 25 Main oil passage 26 Main oil passage 27 Return Bypass Oil Channel 50 Safety switching valve 51 Pneumatic knock-off valve 52 Pneumatic Circuits 53 Pneumatic switching valve 54 Air Tank

Claims

1. It comprises a rotating device rotatably mounted on the vehicle body and a rotating mechanism that rotates this rotating device, The aforementioned rotating mechanism comprises a cylinder that pushes up and rotates the rotating device, a hydraulic circuit that hydraulically drives the cylinder, and a safety device that restricts the hydraulic drive of the cylinder to a safe range. This safety device includes a safety switching valve that restricts the supply of hydraulic fluid from the hydraulic circuit to the cylinder, and a pneumatic knock-off valve that controls the switching of this safety switching valve. The system includes a pneumatic circuit that switches the safety switching valve when the pneumatic knock-off valve is activated, The aforementioned pneumatic knock-off valve is configured to activate in response to the tilt angle of the cylinder caused by the upward pushing motion of the cylinder, thereby switching the safety switching valve to the safety position and restricting the supply of hydraulic fluid to the cylinder. A cargo handling vehicle characterized by the following features.

2. The hydraulic circuit comprises a main switching valve for switching and controlling the supply of hydraulic fluid to the oil tank, hydraulic pump, and cylinder, and the safety switching valve. The aforementioned pneumatic circuit is configured to supply working air from an air tank to a pneumatic switching valve that hydraulically operates the safety switching valve by the switching operation of the pneumatic knock-off valve. The cargo handling vehicle according to feature 1.

3. The aforementioned vehicle consists of a towing vehicle and a towed vehicle that is towed by the towing vehicle, which are detachably connected. The towed vehicle is provided with the rotating device, the cylinder of the rotating mechanism, and the pneumatic knock-off valve and pneumatic circuit of the safety device, and the towing vehicle is also provided with the hydraulic circuit of the rotating mechanism. The hydraulic circuit and cylinder of the aforementioned rotating mechanism are connected by a detachable dedicated oil piping. The cargo handling vehicle according to feature 2.

4. The pneumatic knock-off valve detects the tilt angle of the cylinder by being pressed against the cylinder via the rotating curved surface of the cam. The cargo handling vehicle according to feature 1.

5. The cam is provided with rotatable rollers at the portion that contacts the pneumatic knock-off valve and the cylinder, respectively. The cargo handling vehicle according to feature 4.

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