JP6457380B2 - Transport vehicle - Google Patents

Description

  The present invention relates to a transport vehicle such as a dump truck that is suitably used for transporting loads made of, for example, open-pit mines, quarries, crushed stones mined in mines, or excavated earth and sand.

  In general, a large transport vehicle called a dump truck includes a vessel (loading platform) that can be tilted upward and downward with a rear side as a fulcrum on a frame of a vehicle body. A transport vehicle transports and transports a cargo to be transported (for example, crushed stone and earth and sand) to a transport destination (unloading site, collection site) in a state where a large amount of cargo (for example, crushed stone and earth and sand) is loaded on the vessel ( Patent Documents 1 and 2).

  Here, a hoist cylinder for tilting the vessel upward and downward is provided between the vehicle body and the vessel. The hoist cylinder is supplied with pressure oil from a hydraulic pump via a directional control valve. The directional control valve has a raised position (R) that tilts the vessel upward, a lowered position (L) that tilts the vessel downward, and a float that reduces the hoist cylinder by its own weight and allows the vessel to fall by its own weight. It has a plurality of switching positions consisting of a position (F) and a neutral position (N) that stops the movement of the hoist cylinder. The direction control valve is selectively switched to any one of a total of four switching positions in accordance with manual operation of an operation lever operated by the operator.

  For example, when the transport vehicle is traveling, the operation lever is held at the floating position. Thereby, the vessel continues to be seated on the vehicle body by its own weight, and the hoist cylinder can also be kept in a contracted state by utilizing the own weight on the vessel side. On the other hand, the roads of mine quarries are dirt roads, and there are many rough roads. In such a transport vehicle traveling on the road surface, vibration during traveling increases due to the unevenness of the road surface. At this time, when the vessel is empty, there is a possibility that the vessel floats up (flutters) from the vehicle body due to vibration caused by pushing up from the road surface and collides with the vehicle body when the vessel is seated on the vehicle body. This may cause discomfort to the operator in the cab.

  Therefore, in the case of the transport vehicle according to Patent Document 1, when the vehicle body is in a traveling state and the direction control valve is in the floating position (F), when detecting that the vessel has moved in the direction of lifting from the vehicle body, The directional control valve is controlled to be switched from the floating position to the lowered position. Accordingly, when the vessel tends to lift from the vehicle body, the direction control valve is switched from the floating position to the lowered position, and the vessel can be pressed against the vehicle body side. However, since the directional control valve is controlled after detecting the floating of the vessel, there is a possibility that the pressing of the vessel is delayed.

  On the other hand, the transport vehicle according to Patent Document 2 is configured to provide a throttle at the floating position (F) of the direction control valve. In this case, when the directional control valve is in the floating position (F), the pressure (back pressure) generated between the hydraulic pump and the throttle is applied to the rod side oil chamber of the hoist cylinder, so that the vessel is Can be pressed to the side.

International Publication No. 2008/099691 International Publication No. 2013/146140

  The transport vehicle according to Patent Document 2 generates a pressure for pressing the vessel against the vehicle body by a throttle provided at the floating position (F) of the direction control valve. For this reason, the efficiency of a hydraulic pump may fall with the pressure loss by a throttle.

  An object of the present invention is to provide a transport vehicle that can suppress the rise of a vessel and can suppress a decrease in efficiency of a hydraulic pump.

  The transport vehicle according to the present invention includes a travelable vehicle body, a vessel on the vehicle body that can be tilted upward and downward with a rear side as a fulcrum, and a load is loaded between the vessel and the vessel and the vehicle body. A hoist cylinder that tilts the vessel upward and downward about the fulcrum by extending or contracting the rod, a hydraulic pump, and a direction provided between the hydraulic pump and the hoist cylinder A control valve, a rod-side main line connecting the directional control valve and the rod-side oil chamber of the hoist cylinder, a bottom-side main line connecting the directional control valve and the bottom-side oil chamber of the hoist cylinder, A pilot line for supplying pilot pressure to the directional control valve, and the directional control valve is a raised position for tilting the vessel upward by the hoist cylinder ( ), A lowered position (L) for reducing the hoist cylinder to tilt the vessel downward, and a floating position (F) for reducing the hoist cylinder by its own weight on the vessel side and allowing the vessel to fall by its own weight. And a plurality of switching positions including a neutral position (N) for holding the vessel.

In order to solve the above-described problems, the configuration adopted by the present invention is characterized in that a connection pipe connecting the pilot pipe and the rod-side main pipe or the rod-side oil chamber, and the connection pipe When the directional control valve is in the floating position (F), the pilot pipe and the rod side main pipe or the rod side oil chamber are in an open position, and the directional control valve is in the floating position. A switching valve that is in a closed position that shuts off the communication between the pilot pipe and the rod-side main pipe or the rod-side oil chamber when in a position other than (F), and the directional control valve includes the hydraulic pump And a hoist cylinder, and a first directional control valve and a second directional control valve connected in parallel. The first directional control valve includes the neutral position (N) and the raised position (R ) And floating The second directional control valve is switched to any one of the neutral position (N), the raised position (R), and the lowered position (L). The switching valve is switched to the open position when a part of the pilot pressure supplied to the hydraulic pilot section that switches the first directional control valve to the floating position (F) is supplied. It located in Rukoto.

  The transport vehicle according to the present invention can suppress the floating of the vessel and can suppress the decrease in the efficiency of the hydraulic pump.

It is a front view which shows the dump truck by embodiment. It is a hydraulic circuit diagram which shows the circuit structure which drives a hoist cylinder. It is a hydraulic circuit diagram which shows the state of a directional control valve in a floating position (F). It is a hydraulic circuit diagram which shows the circuit structure by a modification.

  Hereinafter, a case where the embodiment of the transport vehicle according to the present invention is applied to a dump truck that transports crushed stones and earth and sand mined in a mine will be described in detail with reference to the accompanying drawings.

  1 to 3 show an embodiment. In FIG. 1, a dump truck 1 as a representative example of a transport vehicle is tilted upward and downward with a vehicle body 4 that can be driven by front wheels 2 and rear wheels 3 that are wheels, and the rear side of the vehicle body 4 as a fulcrum. And a vessel 5 provided so as to be capable of rolling (undulation).

  The vessel 5 is formed as a large container having a total length of, for example, 10 to 13 meters in order to load a large amount of loads such as crushed stones or earth and sand (hereinafter referred to as earth and sand 6). The vessel 5 is provided on the vehicle body 4 so as to be tiltable upward and downward with the rear side as a fulcrum. That is, the rear side of the vessel 5 is connected to the rear side of the vehicle body 4 via the connecting pin 7 so as to be tiltable. The front side of the vessel 5 is lifted (inclined) upward and downward with the position of the connecting pin 7 as a fulcrum by extending or contracting a hoist cylinder 10 described later.

  The cab 8 is provided on the front side of the vehicle body 4. The cab 8 forms a cab where an operator of the dump truck 1 gets on and off. Inside the cab 8 are provided a driver's seat, an accelerator pedal, a brake pedal, a steering handle (all not shown), an operation lever 38A (see FIG. 2 and FIG. 3) described later, and the like.

  The engine 9 as a prime mover is composed of, for example, a large diesel engine. The engine 9 is provided in the vehicle body 4 on the lower side of the cab 8. The engine 9 rotationally drives a main hydraulic pump 11 and a pilot hydraulic pump 32 (see FIGS. 2 and 3), which will be described later, and the like.

  A pair of hoist cylinders 10 on the left and right are provided between the vessel 5 and the vehicle body 4 so as to be extended or reduced. As shown in FIGS. 2 and 3, the hoist cylinder 10 is composed of a multistage (for example, two-stage) hydraulic cylinder, a so-called telescopic hydraulic cylinder. That is, the hoist cylinder 10 includes a cylindrical outer cylinder portion 10A located on the outer side, and a cylindrical shape in which one end is inserted in the outer cylinder portion 10A so as to be able to expand or contract and the other end protrudes outside the outer cylinder portion 10A. The inner cylinder portion 10B, a rod 10C having one end inserted into the inner cylinder portion 10B so as to be extendable or shrinkable and the other end protruding outside the inner cylinder portion 10B, and an inner cylinder provided on one end side of the rod 10C. The piston 10D slides in the portion 10B.

  The inside of the outer cylinder portion 10A that is a cylinder of the hoist cylinder 10 is defined by the inner cylinder portion 10B, the rod 10C, and the piston 10D into three chambers of rod-side oil chambers 10E and 10F and a bottom-side oil chamber 10G. In this case, the rod-side oil chamber 10F communicates with the rod-side oil chamber 10E via a port 10H provided in the inner cylinder portion 10B. The hoist cylinder 10 tilts (inclines) the vessel 5 upward or downward with a fulcrum on the rear side as a center by extending or contracting the inner cylinder portion 10B and the rod 10C.

  Specifically, when the pressure oil is supplied from the main hydraulic pump 11 into the bottom side oil chamber 10G, the hoist cylinder 10 has the inner cylinder portion 10B that extends downward together with the rod 10C, and the inner cylinder portion 10B. When is fully extended, only the rod 10C further extends downward to the maximum extension position. Thereby, the hoist cylinder 10 rotates (tilts) the vessel 5 to the raised position (soil removal position) inclined obliquely rearward with the connecting pin 7 as a fulcrum.

  On the other hand, in the hoist cylinder 10, when pressure oil is supplied from the main hydraulic pump 11 into the rod side oil chamber 10E in a state where the rod 10C is extended to the maximum, only the rod 10C is first reduced, and thereafter the inner cylinder portion 10B is It contracts to the maximum contraction position together with the rod 10C. As a result, the hoist cylinder 10 rotates (tilts) to the lowered position (traveling position) where the vessel 5 is lowered downward with the connecting pin 7 as a fulcrum.

  Next, a hydraulic circuit for driving the hoist cylinder 10 will be described with reference to FIGS. In this case, FIG. 2 shows a state where the control valve device 17 is in the neutral position (N), and FIG. 3 shows a state where the control valve device 17 is in the floating position (F).

  The main hydraulic pump 11 (hereinafter referred to as the hydraulic pump 11) discharges hydraulic oil stored in the hydraulic oil tank 12 as pressure oil. The hydraulic pump 11 constitutes a hydraulic pressure source (first hydraulic pressure source) that supplies and discharges pressure oil to and from the hoist cylinder 10 together with a hydraulic oil tank 12 that stores hydraulic oil. As shown in FIG. 1, the hydraulic oil tank 12 is located below the vessel 5 and attached to the side surface of the vehicle body 4.

  The hydraulic oil stored in the hydraulic oil tank 12 is sucked into the hydraulic pump 11 when the hydraulic pump 11 is rotationally driven by the engine 9. High pressure oil is discharged into the pump line 13 from the discharge side of the hydraulic pump 11. The pump line 13 connects between the hydraulic pump 11 and a control valve device 17 described later. On the other hand, the return oil from the hoist cylinder 10 is discharged to the hydraulic oil tank 12 through the low-pressure return line 14. The return line 14 returns the pressure oil discharged from the hydraulic pump 11 and passing through the control valve device 17 to the hydraulic oil tank 12.

  The rod side main pipe line 15 connects the control valve device 17 and the rod side oil chambers 10 </ b> E and 10 </ b> F of the hoist cylinder 10. The bottom side main pipeline 16 connects the control valve device 17 and the bottom side oil chamber 10 </ b> G of the hoist cylinder 10. The rod-side main pipeline 15 and the bottom-side main pipeline 16 are connected to a hydraulic source (hydraulic pump 11 and hydraulic oil tank 12) via a control valve device 17, respectively, and a pair of main pipelines serving as actuator pipelines are connected. It is composed.

  The rod side main pipeline 15 supplies the pressure oil from the hydraulic pump 11 to the rod side oil chambers 10E and 10F of the hoist cylinder 10 via the control valve device 17. Further, the rod-side main pipeline 15 discharges the pressure oil in the rod-side oil chambers 10 </ b> E and 10 </ b> F to the hydraulic oil tank 12 through the control valve device 17. On the other hand, the bottom side main pipeline 16 supplies the pressure oil from the hydraulic pump 11 to the bottom side oil chamber 10 </ b> G of the hoist cylinder 10 via the control valve device 17. Further, the bottom side main pipeline 16 discharges the pressure oil in the bottom side oil chamber 10 </ b> G to the hydraulic oil tank 12 via the control valve device 17.

  The control valve device 17 is provided between the hydraulic source (hydraulic pump 11, hydraulic oil tank 12) and the hoist cylinder 10. The control valve device 17 controls supply and discharge of pressure oil to the hoist cylinder 10. For this purpose, the control valve device 17 includes a high-pressure side oil passage 18, a low-pressure side oil passage 19, 20, a center bypass oil passage 21, a first directional control valve 22 and a second directional control valve 23 as directional control valves. Actuator connection oil passages 24A, 24B, 25A, 25B, detour oil passages 26A, 26B, 27A, 27B, check valves 28A, 28B, 30A, 30B, and relief valves 29A, 29B are included.

  In this case, the first directional control valve 22 and the second directional control valve 23 are connected in parallel to each other via the high pressure side oil passage 18, the low pressure side oil passages 19 and 20, and the center bypass oil passage 21. In other words, the directional control valve constituting the control valve device 17 includes the first directional control valve 22 and the second directional control valve 23 connected in parallel between the hydraulic pump 11 and the hoist cylinder 10. ing.

  One end of the high-pressure side oil passage 18 is connected to the discharge side of the hydraulic pump 11 via the pump conduit 13, and the other end is connected to the second directional control valve 23. Further, the high-pressure side oil passage 18 is branched from an intermediate portion and connected to the first directional control valve 22. One low pressure side oil passage 19 is arranged on the return side of the first directional control valve 22 and connects an actuator connection oil passage 24A, 24B, which will be described later, to the hydraulic oil tank 12 via the return conduit 14. is there. The other low-pressure side oil passage 20 is arranged on the return side of the second directional control valve 23, and connects an actuator connection oil passage 25B described later to the hydraulic oil tank 12 via the return conduit 14.

  The center bypass oil passage 21 has a second position when the first and second directional control valves 22 and 23 are both in the neutral position (N) and when the first directional control valve 22 is in the floating position (F). When the direction control valve 23 is in the neutral position (N), the pump line 13 and the return line 14 are communicated. As a result, the hydraulic pump 11 is unloaded, and its discharge pressure (pressure in the pump line 13) is kept at a low pressure close to the tank pressure.

  A pair of actuator connection oil passages 24 </ b> A and 24 </ b> B are provided on the outflow side of the first directional control valve 22. The actuator connection oil passages 24A and 24B are connected to the rod side oil chambers 10E and 10F and the bottom side oil chamber 10G of the hoist cylinder 10 via the rod side main pipeline 15 or the bottom side main pipeline 16, respectively. At the same time, the actuator connection oil passages 24A and 24B are connected to the return conduit 14 (the hydraulic oil tank 12) via first bypass oil passages 26A and 26B, which will be described later.

  A pair of actuator connection oil passages 25 </ b> A and 25 </ b> B are provided on the outflow side of the second directional control valve 23. The actuator connection oil passages 25A and 25B are connected to the rod side oil chambers 10E and 10F and the bottom side oil chamber 10G of the hoist cylinder 10 via the rod side main pipeline 15 or the bottom side main pipeline 16, respectively. At the same time, the actuator connection oil passages 25A and 25B are connected to the return conduit 14 (the hydraulic oil tank 12) via second bypass oil passages 27A and 27B, which will be described later.

  The first directional control valve 22 and the second directional control valve 23 are each configured by, for example, a 6-port, 3-position hydraulic pilot type directional control valve. The first directional control valve 22 has a pair of hydraulic pilot portions 22A and 22B. The first directional control valve 22 is switched from the neutral position (N) to the raised position (R) when a pilot pressure is supplied from a solenoid valve 35 for raising operation described later to the hydraulic pilot portion 22A. On the other hand, the first directional control valve 22 is switched from the neutral position (N) to the floating position (F) when a pilot pressure is supplied to the hydraulic pilot unit 22B from an electromagnetic valve 37 for floating operation described later. That is, the first directional control valve 22 is configured to switch to any one of the neutral position (N), the raised position (R), and the floating position (F).

  The second directional control valve 23 has a pair of hydraulic pilot portions 23A and 23B. The second directional control valve 23 is switched from the neutral position (N) to the raised position (R) when the pilot pressure is supplied from the solenoid valve 35 for raising operation to the hydraulic pilot portion 23A. On the other hand, the second directional control valve 23 is switched from the neutral position (N) to the lowered position (L) when a pilot pressure is supplied to the hydraulic pilot part 23B from a solenoid valve 36 for lowering operation, which will be described later. That is, the second direction control valve 23 is configured to switch to any one of the neutral position (N), the raised position (R), and the lowered position (L).

  As described above, the first directional control valve 22 and the second directional control valve 23 that are directional control valves of the control valve device 17 are in the neutral position (N), the raised position (R), the lowered position (L), and the floating position. It has a plurality of switching positions consisting of position (F). The first directional control valve 22 and the second directional control valve 23 are switched to any one of the switching positions.

  Here, a case where the control valve device 17 is in the neutral position (N) will be described. In this case, as shown in FIG. 2, the first and second directional control valves 22 and 23 are both arranged at the neutral position (N), thereby stopping the movement of the hoist cylinder 10 and holding the vessel 5. The holding position. At the neutral position (N) that is the holding position, the supply and discharge of pressure oil to and from the hoist cylinder 10 via the actuator connection oil passages 24A and 24B and the actuator connection oil passages 25A and 25B are stopped.

  A case where the control valve device 17 is in the raised position will be described. In this case, the pilot pressure is supplied to the hydraulic pilot portions 22A and 23A of the first and second directional control valves 22 and 23 from a solenoid valve 35 for raising operation, which will be described later, and the first and second directional control valves. 22 and 23 are both switched from the neutral position (N) to the raised position (R). When the first and second directional control valves 22 and 23 are in the raised position (R), the pressure oil from the hydraulic pump 11 is supplied from the pump line 13, the high-pressure side oil path 18, and the first and second directional control valves. 22 and 23, actuator connection oil passages 24 </ b> B and 25 </ b> B, and the bottom main pipeline 16 are supplied into the bottom oil chamber 10 </ b> G of the hoist cylinder 10.

  At this time, the pressure oil in the rod-side oil chambers 10E and 10F is changed to the rod-side main pipeline 15, the actuator connection oil passage 24A, the first directional control valve 22 by switching to the raised position (R). The oil is returned to the hydraulic oil tank 12 through the direction control valve 22, the low pressure side oil passage 19 and the return pipe 14. Thereby, the inner cylinder part 10B and / or the rod 10C of the hoist cylinder 10 are extended by the pressure oil in the bottom side oil chamber 10G to tilt the vessel 5 to the discharge position. That is, at this time, both the first and second directional control valves 22 and 23 of the control valve device 17 are arranged at the raised position (R), and the hoist cylinder 10 extends the vessel 5 upward by extending with hydraulic pressure. Inclined.

  On the other hand, a case where the control valve device 17 is in the lowered position will be described. In this case, a pilot pressure is supplied from a solenoid valve 36 for lowering operation, which will be described later, to the hydraulic pilot portion 23B of the second directional control valve 23, and the second directional control valve 23 is moved from the neutral position (N) to the lowered position. Switch to (L). The first directional control valve 22 is disposed at the neutral position (N). When the second directional control valve 23 is in the lowered position (L), the pressure oil from the hydraulic pump 11 is pump line 13, high pressure side oil path 18, second directional control valve 23, actuator connection oil path 25A, rod The gas is supplied into the rod side oil chambers 10E and 10F of the hoist cylinder 10 through the side main pipeline 15. The pressure oil in the bottom side oil chamber 10G is returned to the hydraulic oil tank 12 via the bottom side main pipe line 16, the actuator connection oil path 25B, the second directional control valve 23, the low pressure side oil path 20, and the return pipe line 14. It is.

  Thereby, the inner cylinder part 10B and / or the rod 10C of the hoist cylinder 10 are contracted by the pressure oil in the rod side oil chambers 10E and 10F, and the vessel 5 is tilted downward to the traveling position shown in FIG. That is, at this time, the second directional control valve 23 of the control valve device 17 is arranged in the lowered position (L), and the hoist cylinder 10 is contracted by the hydraulic pressure to move the vessel 5 to the position where the vessel 5 is seated on the vehicle body 4. And lowering (lowering).

  Next, a case where the control valve device 17 is in the floating position will be described. In this case, as shown in FIG. 3, a pilot pressure is supplied to a hydraulic pilot portion 22B of the first directional control valve 22 from a later-described electromagnetic valve 37 for floating operation, and the first directional control valve 22 is moved to the neutral position. Switch from (N) to floating position (F). The second directional control valve 23 is disposed at the neutral position (N). When the first directional control valve 22 reaches the floating position (F), the actuator connection oil passage 24B is connected to the low-pressure side oil passage 19 and the return conduit 14 via the first directional control valve 22. On the other hand, the other actuator connection oil passages 24A and 25A are connected to the return pipe 14 side via detour oil passages 26A and 27A and check valves 28A and 30A described later.

  As a result, the hoist cylinder 10 is reduced in accordance with the load (self-weight) from the vessel 5, and the pressure oil in the bottom side oil chamber 10 </ b> G is supplied from the bottom side main pipeline 16, the actuator connection oil passage 24 </ b> B, and the first directional control valve 22. The oil is discharged toward the hydraulic oil tank 12 through the low-pressure side oil passage 19 and the return pipe 14. On the other hand, in the rod side oil chambers 10E and 10F, the hydraulic oil in the hydraulic oil tank 12 is returned to the return pipe 14, check valves 28A and 30A, bypass oil paths 26A and 27A, actuator connection oil paths 24A and 25A, and the rod side. It is replenished via the main line 15. That is, at this time, the first directional control valve 22 of the control valve device 17 is disposed at a floating position (F) that allows the vessel 5 to fall by its own weight.

  The first bypass oil passages 26 </ b> A and 26 </ b> B bypass the first directional control valve 22 and are provided between the actuator connection oil passages 24 </ b> A and 24 </ b> B and the hydraulic oil tank 12. One of the first bypass oil passages 26A and 26B has one side connected to a middle portion of the actuator connection oil passage 24A, and the other side connected to the hydraulic oil tank 12 via the return conduit 14. ing. The other bypass oil passage 26 </ b> B has one side connected to an intermediate portion of the actuator connection oil passage 24 </ b> B and the other side connected to the hydraulic oil tank 12 via the return pipe 14.

  In this case, one bypass oil passage 26 </ b> A, together with the actuator connection oil passage 24 </ b> A and the return conduit 14, constitutes a tank conduit that connects the rod-side main conduit 15 and the hydraulic oil tank 12. As will be described later, the one bypass oil passage 26A is provided with a relief valve 29A for relieving the excess pressure of the rod side main conduit 15 to the hydraulic oil tank 12.

  The second bypass oil passages 27 </ b> A and 27 </ b> B bypass the second direction control valve 23 and are provided between the actuator connection oil passages 25 </ b> A and 25 </ b> B and the hydraulic oil tank 12. One of the second bypass oil passages 27A and 27B has one side connected to an intermediate portion of the actuator connection oil passage 25A, and the other side connected to the hydraulic oil tank 12 via the return conduit 14. ing. The other bypass oil passage 27 </ b> B has one side connected to an intermediate portion of the actuator connection oil passage 25 </ b> B and the other side connected to the hydraulic oil tank 12 through the return pipe 14.

  The make-up check valves 28A and 28B are disposed on the first directional control valve 22 side of the control valve device 17. The check valves 28A and 28B are provided in the middle of first bypass oil passages 26A and 26B that bypass the outflow side of the first directional control valve 22. One of the check valves 28A and 28B is such that the hydraulic oil in the hydraulic oil tank 12 is supplied to the rod of the hoist cylinder 10 via the first bypass oil passage 26A, the actuator connection oil passage 24A, and the rod side main conduit 15. Permits flow toward the side oil chambers 10E and 10F, and prevents flow in the opposite direction. Thereby, in the reduction stroke of the hoist cylinder 10, the rod side oil chambers 10E and 10F of the hoist cylinder 10 are prevented from becoming negative pressure by the hydraulic oil supplied through the check valve 28A.

  On the other hand, the other check valve 28B allows the hydraulic oil in the hydraulic oil tank 12 to enter the bottom oil chamber 10G of the hoist cylinder 10 via the first bypass oil passage 26B, the actuator connection oil passage 24B, and the bottom main pipe passage 16. Allow it to circulate and prevent it from flowing in the opposite direction. This prevents the bottom side oil chamber 10G of the hoist cylinder 10 from becoming negative pressure due to the hydraulic oil replenished via the check valve 28B during the extension stroke of the hoist cylinder 10.

  The relief valves 29A and 29B for preventing overload are disposed on the first directional control valve 22 side of the control valve device 17. The relief valves 29A and 29B are provided in parallel with the check valves 28A and 28B in the middle of the first bypass oil passages 26A and 26B that bypass the outflow side of the first directional control valve 22. One of the relief valves 29A and 29B is provided in the first bypass oil passage 26A, and when an overload in the extending direction acts on the hoist cylinder 10, the rod side oil chambers 10E and 10F side Open to relieve overpressure. The other relief valve 29B is provided in the first bypass oil passage 26B, and when the overload in the reduction direction acts on the hoist cylinder 10, the excess pressure on the bottom side oil chamber 10G side is relieved to the hydraulic oil tank 12. To open.

  The make-up check valves 30A and 30B are disposed on the second directional control valve 23 side of the control valve device 17. The check valves 30A and 30B are provided in the middle of second bypass oil passages 27A and 27B that bypass the outflow side of the second directional control valve 23. One of the check valves 30A and 30B is such that the hydraulic oil in the hydraulic oil tank 12 is supplied to the rod of the hoist cylinder 10 through the second bypass oil passage 27A, the actuator connection oil passage 25A, and the rod-side main conduit 15. Permits flow toward the side oil chambers 10E and 10F, and prevents flow in the opposite direction. Thereby, in the reduction stroke of the hoist cylinder 10, the check valve 30 </ b> A replenishes the rod-side oil chambers 10 </ b> E and 10 </ b> F of the hoist cylinder 10, thereby preventing negative pressure.

  On the other hand, the other check valve 30B allows the hydraulic oil in the hydraulic oil tank 12 to enter the bottom side oil chamber 10G of the hoist cylinder 10 via the second bypass oil path 27B, the actuator connection oil path 25B, and the bottom side main pipe line 16. Allow it to circulate and prevent it from flowing in the opposite direction. Thereby, in the expansion stroke of the hoist cylinder 10, the check valve 30B supplies hydraulic oil to the bottom side oil chamber 10G of the hoist cylinder 10 and thereby prevents a negative pressure.

  The main relief valve 31 is provided between the pump line 13 (high-pressure side oil path 18) and the hydraulic oil tank 12 (return line 14). The relief valve 31 determines the maximum discharge pressure of the hydraulic pump 11 and suppresses the pressure in the pump line 13 to be equal to or lower than the maximum discharge pressure. That is, the relief valve 31 is opened when an excessive pressure exceeding the maximum discharge pressure is generated in the pump line 13, and the excess pressure at this time is relieved to the hydraulic oil tank 12 side.

  Next, the electromagnetic valves 35, 36, and 37 that control the control valve device 17, the operation lever device 38, the controller 40, and the like will be described.

  The pilot hydraulic pump 32 is provided separately from the hydraulic pump 11. Similar to the hydraulic pump 11, the pilot hydraulic pump 32 discharges hydraulic oil stored in the hydraulic oil tank 12 as pressure oil. The pilot hydraulic pump 32, together with the hydraulic oil tank 12, supplies a hydraulic pressure source (second hydraulic pressure) that supplies pilot pressure to the directional control valves (first directional control valve 22 and second directional control valve 23) of the control valve device 17. Source).

  The pilot hydraulic pump 32 is driven to rotate by the engine 9 to increase the pressure of the hydraulic oil in the hydraulic oil tank 12 and discharge it into the pilot pipe line 33. The pressure oil discharged into the pilot pipe line 33 is maintained at a predetermined pilot pressure by the pilot relief valve 34. The pilot line 33 supplies pilot pressure for switching the first directional control valve 22 and the second directional control valve 23 via the electromagnetic valves 35, 36, and 37 to the first directional control valve 22 and the second directional control valve 22. The directional control valve 23 is supplied.

  The electromagnetic valves 35, 36, and 37 are for supplying pilot pressure to the hydraulic pilot portions 22 A, 22 B, 23 A, and 23 B of the first and second directional control valves 22 and 23 of the control valve device 17. The electromagnetic valves 35, 36, and 37 are provided in parallel in the middle part of the pilot pipe line 33. The solenoid valves 35, 36, and 37 are connected to the controller 40, respectively. The electromagnetic valves 35, 36, and 37 are individually opened and closed in accordance with the operation of an operation lever device 38, which will be described later, and switched to the first and second directional control valves 22 and 23 of the control valve device 17 when the valves are opened. A pilot pressure for control is supplied.

  Among the solenoid valves 35, 36, and 37, the solenoid valve 35 for the raising operation is connected to the hydraulic pilot portions 22A and 23A of the first and second directional control valves 22 and 23 via the pilot pipe 33A for the raising operation. ing. The electromagnetic valve 35 is switched from the valve closing position (a) to the valve opening position (b) according to the excitation signal from the controller 40. At the valve open position (b), the pilot pressure for raising operation is supplied from the pilot line 33 to the hydraulic pilot portions 22A and 23A of the first and second directional control valves 22 and 23 via the pilot line 33A for raising operation. Is supplied. Thus, the first and second directional control valves 22 and 23 are switched from the neutral position (N) shown in FIG. 2 to the raised position (R).

  The lowering solenoid valve 36 is connected to the hydraulic pilot portion 23B of the second directional control valve 23 via the lowering operation pilot line 33B. The electromagnetic valve 36 is switched from the valve closing position (a) to the valve opening position (b) according to the excitation signal from the controller 40. At the valve opening position (b), the pilot pressure for lowering operation is supplied from the pilot line 33 to the hydraulic pilot portion 23B of the second directional control valve 23 via the pilot line 33B for lowering operation. Thereby, the second directional control valve 23 is switched from the neutral position (N) shown in FIG. 2 to the lowered position (L). At this time, since the electromagnetic valves 35 and 37 are demagnetized and are in the closed position (a), the first directional control valve 22 is disposed in the neutral position (N).

  On the other hand, the solenoid valve 37 for floating operation is connected to the hydraulic pilot portion 22B of the first directional control valve 22 via a pilot line 33C for floating operation. The electromagnetic valve 37 is switched from the valve closing position (a) to the valve opening position (b) according to the excitation signal from the controller 40. In the valve opening position (b), the pilot pressure for the floating operation is supplied from the pilot pipe line 33 to the hydraulic pilot portion 22B of the first directional control valve 22. Thereby, the first directional control valve 22 is switched from the neutral position (N) shown in FIG. 2 to the floating position (F) shown in FIG. At this time, since the electromagnetic valves 35 and 36 are demagnetized and are in the closed position (a), the second directional control valve 23 is disposed in the neutral position (N).

  The operation lever device 38 is an operation device that performs a switching operation of the first and second directional control valves 22 and 23. The operation lever device 38 is constituted by an electric lever device, for example, and is provided in the vicinity of the driver's seat of the cab 8. The operation lever device 38 has an operation lever 38A that is manually tilted by an operator in the cab 8. The operation lever 38A corresponds to each switching position of the first and second directional control valves 22, 23, that is, the neutral position (N), the raised position (R), the lowered position (L), and the floating position (F). Thus, it is tilted to any one of the neutral position (N), the raised position (R), the lowered position (L), and the floating position (F).

  The lever sensor 39 is attached to the operation lever device 38. The lever sensor 39 detects the operation position (lever position) of the operation lever 38A by the operator, and outputs a detection signal to the controller 40 described later. Specifically, in the lever sensor 39, the operation lever 38A of the operation lever device 38 is in any position of the neutral position (N), the raised position (R), the lowered position (L), and the floating position (F). To detect. The operation position of the operation lever 38A detected by the lever sensor 39 corresponds to the switching position of the first and second directional control valves 22 and 23. That is, the lever sensor 39 can detect the switching position of the first and second directional control valves 22 and 23 by detecting the position of the operation lever 38A.

  The controller 40 is composed of a microcomputer, and an input side thereof is connected to the lever sensor 39 and the like, and an output side thereof is connected to the electromagnetic valves 35, 36, 37 and the like. The controller 40 determines the operation position of the operation lever 38A based on the detection signal from the lever sensor 39, and in order to make the operation position of the operation lever 38A correspond to the switching position of the control valve device 17, the electromagnetic valves 35, 36, 37 outputs an excitation signal.

  By the way, the transport vehicle by the above-mentioned patent document 2 generates the pressure for pressing a vessel on the vehicle body side by the throttle provided in the floating position of the direction control valve. For this reason, the efficiency of a hydraulic pump may fall with the pressure loss by a throttle. On the other hand, when the directional control valve is in the floating position (F), the pilot pressure for switching the directional control valve is supplied to the rod side oil chamber of the hoist cylinder, thereby pressing the vessel against the vehicle body side. It is possible. In this case, for example, an electromagnetic switching valve (solenoid valve) is provided in the middle of the pilot line, and the pilot pressure of the pilot line can be supplied to the rod side oil chamber of the hoist cylinder via the electromagnetic switching valve. It is possible to do so.

  For example, the lever sensor detects that the direction control valve is in the floating position (F). The seat sensor detects that the vessel is seated on the vehicle body. The suspension pressure sensor detects that the vessel is empty. Furthermore, it is detected by a speed sensor that the vehicle is running. When the controller that switches the electromagnetic switching valve detects these, it supplies the pilot pressure of the pilot line to the rod side oil chamber of the hoist cylinder by switching the electromagnetic switching valve to the communication position. Can be considered. However, in this case, in addition to changing the hydraulic circuit, there is a possibility that the assembling work becomes troublesome, for example, it is necessary to change the software of the controller for controlling the electromagnetic switching valve.

  Therefore, in the embodiment, the pilot line 33 is provided with a hydraulic pilot type switching valve 41, and the pilot pressure of the pilot line 33 is supplied to the rod side oil chambers 10 </ b> E and 10 </ b> F of the hoist cylinder 10 via the switching valve 41. It is configured so that it can be supplied. For this purpose, a connecting pipe line 42 that connects the pilot pipe line 33 and the rod side main pipe line 15 is provided between the pilot pipe line 33 and the rod side main pipe line 15. A hydraulic pilot type switching valve 41 is provided in the middle of the connection pipe line 42.

  The switching valve 41 is constituted by, for example, a 2-port 2-position hydraulic pilot type switching valve. The hydraulic pilot section of the switching valve 41 is connected to the floating operation pilot line 33C. Thereby, the switching valve 41 is switched to the open position (d) by being supplied with a part of the pilot pressure supplied to the hydraulic pilot part 22B that switches the first directional control valve 22 to the floating position (F). Change. In addition, you may comprise the switching valve 41 by the sequence valve of an external pilot system, for example.

  As shown in FIG. 2, the switching valve 41 is configured such that the first and second directional control valves 22 and 23 are at positions other than the floating position (F) (that is, the neutral position (N), the raised position (R), or the lowered position. (L), the closed position (c) at which the communication between the pilot pipe line 33 and the rod side main pipe line 15 is cut off. As shown in FIG. 3, when the first and second directional control valves 22 and 23 are in the floating position (F), the switching valve 41 is supplied with switching pilot pressure through the floating operation pilot line 33C. Thus, an open position (d) for communicating the pilot pipe line 33 and the rod side main pipe line 15 is established.

  As a result, the pilot pressure in the pilot line 33 is supplied to the rod-side oil chambers 10E and 10F of the hoist cylinder 10, and the hoist cylinder 10 generates thrust (contraction force) in the direction of reducing the rod 10C. That is, as indicated by an arrow F in FIG. 1, a thrust F (contraction force F) is applied to the vessel 5 as a downward force from the hoist cylinder 10. As a result, the vessel 5 can be pressed to the vehicle body 4 side by the hoist cylinder 10, and the floating of the vessel 5 can be suppressed during traveling.

  On the other hand, a relief valve 29 </ b> A is provided in the bypass oil passage 26 </ b> A between the rod side main pipeline 15 and the hydraulic oil tank 12. For this reason, when the switching valve 41 is in the open position (d), the vessel 5 is lifted against the pilot pressure supplied to the rod-side oil chambers 10E and 10F of the hoist cylinder 10, thereby Even if the pressure rises, the excess pressure can be relieved by the relief valve 29A.

  Further, the connecting pipe 42 is provided with a throttle 43 located between the switching valve 41 and the rod side main pipe 15. The restrictor 43 reduces the flow area of the connection pipe line 42 between the switching valve 41 and the rod side main pipe line 15. For this reason, for example, even if the pressure of the rod side main pipe line 15 rises by raising the vessel 5, the switching valve 41 side can be made lower than the throttle side 43 than the rod side main pipe line 15 side. Thereby, it is possible to easily relieve the excess pressure in the rod side main pipe line 15 by the relief valve 29A.

  The dump truck 1 according to the present embodiment has the above-described configuration, and the operation thereof will be described next.

  In a quarry such as a mine, for example, a large hydraulic excavator (not shown) is used to load earth and sand 6 serving as luggage on the vessel 5. At this time, the vessel 5 is placed at the travel position shown in FIG. 1, and the dump truck 1 carries it toward the unloading site with a large amount of earth and sand 6 loaded on the vessel 5.

  When the operator in the cab 8 manually tilts the operating lever 38A of the operating lever device 38 from the neutral position (N) to the raised position (R) at the unloading site, the controller 40 lifts the solenoid valve. An excitation signal is output to 35. Thereby, the solenoid valve 35 for raising operation is switched from the valve closing position (a) to the valve opening position (b), and the hydraulic pilot part of the first and second directional control valves 22 and 23 is switched from the pilot line 33. Pilot pressure for raising operation is supplied toward 22A and 23A.

  As a result, the first and second directional control valves 22, 23 are switched from the neutral position (N) to the raised position (R). As a result, the pressure oil from the hydraulic pump 11 passes through the pump line 13, the high pressure side oil path 18, the first and second directional control valves 22 and 23, the actuator connection oil paths 24B and 25B, and the bottom side main line 16. To the bottom oil chamber 10G of the hoist cylinder 10. The pressure oil in the rod side oil chambers 10E and 10F is supplied to the hydraulic oil tank 12 via the rod side main pipe line 15, the actuator connection oil path 24A, the first direction control valve 22, the low pressure side oil path 19 and the return pipe line 14. Returned to.

  Thereby, the inner cylinder part 10B and / or the rod 10C of the hoist cylinder 10 are extended by the pressure oil in the bottom side oil chamber 10G. That is, the dump truck 1 can be discharged toward the unloading site so that the sediment 5 in the vessel 5 slides downward when the vessel 5 rotates in an inclined posture with the connecting pin 7 as a fulcrum. it can.

  At this time, when the operator releases his hand from the operation lever 38A, the operation lever 38A is automatically returned to the neutral position (N) by a return spring (not shown). Therefore, the signal output from the controller 40 to the raising solenoid valve 35 is demagnetized (OFF), and the raising solenoid valve 35 returns to the valve closing position (a) shown in FIG. As a result, the first and second directional control valves 22 and 23 automatically return to the neutral position (N), and supply of pressure oil to the bottom side oil chamber 10G and the rod side oil chambers 10E and 10F of the hoist cylinder 10; Stop discharging. Therefore, the hoist cylinder 10 can keep the inner cylinder portion 10B and the rod 10C in the extended state, and can temporarily stop the vessel 5 in the inclined posture.

  Next, when the discharging operation of the earth and sand 6 is completed, the operator manually tilts the operation lever 38A from the neutral position (N) to the floating position (F), so that the controller 40 switches the electromagnetic lever 37 for the floating operation. An excitation signal is output. As a result, as shown in FIG. 3, the solenoid valve 37 for floating operation is switched from the valve closing position (a) to the valve opening position (b), and the hydraulic pressure of the first directional control valve 22 from the pilot line 33 is changed. Pilot pressure for floating operation is supplied toward the pilot portion 22B.

  Thereby, the first directional control valve 22 is switched from the neutral position (N) to the floating position (F). At this time, since the electromagnetic valves 35 and 36 are demagnetized and are in the closed position (a), the second directional control valve 23 is disposed in the neutral position (N). As a result, the actuator connection oil passage 24 </ b> B is connected to the low pressure side oil passage 19 and the return conduit 14 via the first directional control valve 22. The actuator connection oil passage 24A is connected to the return conduit 14 side via the check valve 28A. Further, the other actuator connection oil passage 25A is connected to the low-pressure side oil passage 20 and the return conduit 14 via the check valve 30A.

  As a result, the hoist cylinder 10 is reduced according to the load (self-weight) from the vessel 5. That is, the pressure oil in the bottom side oil chamber 10G is discharged toward the hydraulic oil tank 12, and the rod side oil chambers 10E and 10F have hydraulic oil via the check valve 28A and / or the check valve 30A. The hydraulic oil in the tank 12 is replenished. As a result, the hoist cylinder 10 can lower the vessel 5 to the travel position shown in FIG. 1 by allowing the vessel 5 to fall due to its own weight, and the vessel 5 can be seated on the vehicle body 4.

  On the other hand, when the dump truck 1 is tilted due to unevenness on the work site, sloping ground, etc., the vessel 5 is lowered by its own weight even if the first and second directional control valves 22 and 23 are switched to the floating position (F). There are things that do not. In such a case, when the operator tilts the operation lever 38A to the lowered position (L), an excitation signal is output from the controller 40 to the electromagnetic valve 36 for the lowering operation. As a result, the solenoid valve 36 for lowering operation is switched from the valve closing position (a) to the valve opening position (b) and lowered from the pilot line 33 toward the hydraulic pilot portion 23B of the second directional control valve 23. Pilot pressure for operation is supplied.

  Thereby, the second directional control valve 23 is switched from the neutral position (N) to the lowered position (L). At this time, since the electromagnetic valves 35 and 37 are demagnetized and are in the closed position (a), the first directional control valve 22 is disposed in the neutral position (N). As a result, the pressure oil from the hydraulic pump 11 is supplied to the rod of the hoist cylinder 10 via the pump line 13, the high pressure side oil path 18, the second direction control valve 23, the actuator connection oil path 25 </ b> A, and the rod side main line 15. The oil is supplied into the side oil chambers 10E and 10F. The pressure oil in the bottom side oil chamber 10G is returned to the hydraulic oil tank 12 via the bottom side main pipe line 16, the actuator connection oil path 25B, the second directional control valve 23, the low pressure side oil path 20, and the return pipe line 14. It is.

  As a result, the hoist cylinder 10 is contracted by the pressure oil supplied into the rod-side oil chambers 10E and 10F, so that the inner cylinder portion 10B and / or the rod 10C are reduced into the outer cylinder portion 10A, and the vessel 5 is replaced with the hoist cylinder 10. 1 can be rotated downward to the travel position shown in FIG. 1, and the vessel 5 can be forcibly seated on the vehicle body 4.

  However, when the first and second directional control valves 22 and 23 are switched to the lowered position (L) in this way, the hoist cylinder 10 is contracted by hydraulic pressure, so that an extra load is applied to the vessel 5 and the vehicle body 4. There is a possibility to give. After that, when the position is switched to the lowered position (L), the vessel 5 remains strongly pressed on the vehicle body 4, and the oil pressure from the hoist cylinder 10 is excessive on the contact surface between the vessel 5 and the vehicle body 4. Acts as a heavy load. Therefore, the operator of the dump truck 1 self-holds the operation lever 38A at the floating position (F) when the vehicle is traveling. As a result, the first and second directional control valves 22 and 23 are switched to the floating position (F), the vessel 5 continues to be seated on the vehicle body 4 by its own weight, and the hoist cylinder 10 also uses its own weight on the vessel 5 side. Can be kept in a reduced state.

  However, when the first and second directional control valves 22 and 23 are moved to the floating position (F) and the vessel 5 is empty, the vessel 5 is moved away from the vehicle body 4 due to vibration caused by pushing up from the road surface. When the vessel 5 is lifted and is seated on the vehicle body 4, there is a possibility of colliding with the vehicle body 4. Thereby, there is a possibility that an operator in the cab 8 may feel uncomfortable.

  On the other hand, in the present embodiment, when the first and second directional control valves 22 and 23 are in the floating position (F), the switching valve 41 provided in the middle of the connection pipeline 42 is a pilot pipe. It becomes an open position (d) which connects the path 33 and the rod side main pipeline 15 (rod side oil chambers 10E, 10F). As a result, the pilot pressure in the pilot line 33 is supplied to the rod-side oil chambers 10E and 10F of the hoist cylinder 10, and a thrust F (contraction force F) in the direction of reducing the rod 10C is generated in the hoist cylinder 10. . As a result, the vessel 5 can be pressed against the vehicle body 4 by the hoist cylinder 10.

  That is, when traveling with the first and second directional control valves 22 and 23 in the floating position (F), a force in the direction of lifting from the vehicle body 4 is applied to the vessel 5 as the road surface irregularities pass. In addition, the vessel 5 can be seated on the vehicle body 4 by the thrust F of the hoist cylinder 10, and the floating (flapping) of the vessel 5 can be suppressed. In this case, since it is not necessary to provide a throttle on the upstream side of the hydraulic pump 11 for supplying pressure oil to the hoist cylinder 10, a reduction in efficiency of the hydraulic pump 11 can be suppressed as compared with a configuration in which a throttle is provided. Can do.

  According to the embodiment, the relief valve 29A is provided in the tank conduit that connects the rod-side main conduit 15 and the hydraulic oil tank 12, more specifically, in the bypass oil passage 26A. For this reason, when the vessel 5 floats up against the pilot pressure supplied to the rod-side oil chambers 10E and 10F of the hoist cylinder 10 and the pressure in the rod-side main pipe 15 (rod-side oil chambers 10E and 10F) increases. The excess pressure in the rod side main pipeline 15 can be relieved by the relief valve 29A. Thereby, it can suppress that the pressure of the pilot side 33 connected with the rod side main pipeline 15 and this rod side main pipeline 15 becomes excessive, and the durability of the apparatus by the side of the pilot pipeline 33 including the switching valve 41 can be made. Can be secured.

  According to the embodiment, the throttle 43 is provided in the connection pipeline 42. For this reason, when the vessel 5 floats up against the pilot pressure supplied to the rod-side oil chambers 10E and 10F of the hoist cylinder 10 and the pressure in the rod-side main pipe 15 (rod-side oil chambers 10E and 10F) increases. The throttle 43 can make the switching valve 41 side lower than the throttle 43 than the rod side main pipe 15 side. Thereby, the durability of the equipment on the pilot line 33 side including the switching valve 41 can be ensured. In addition, since the bypass oil passage 26A serving as the tank conduit is provided with the relief valve 29A, it is possible to easily relieve the excess pressure in the rod-side main conduit 15 that has been increased in pressure by the throttle 43 from the relief valve 29A. For this reason, the durability of the equipment on the pilot pipe line 33 side including the switching valve 41 can be ensured also from this aspect.

  According to the embodiment, the direction control valve of the control valve device 17 includes the first direction control valve 22 and the second direction control valve 23 connected in parallel between the hydraulic pump 11 and the hoist cylinder 10. doing. The switching valve 41 is switched to the open position (d) when a part of the pilot pressure supplied to the hydraulic pilot unit 22B that switches the first directional control valve 22 to the floating position (F) is supplied. It is configured. For this reason, even if the electromagnetic switching valve is not used, when the first directional control valve 22 is in the floating position (F), the pilot pressure in the pilot line 33 is reduced to the rod side oil chamber 10E of the hoist cylinder 10. 10F. Thereby, the software of the controller 40 does not need to be changed, and the switching valve 41 can be easily assembled as compared with the electromagnetic switching valve.

  In the above-described embodiment, the case in which the pilot pipeline 33 and the rod-side main pipeline 15 are connected by the connection pipeline 42 is described as an example. However, the present invention is not limited to this, and, for example, as shown in the modification shown in FIG. It is good also as a structure which connects directly (without going through).

  Also in this case, when the first and second directional control valves 22 and 23 are in the floating position (F), the switching valve 41 provided in the middle of the connection pipeline 51 is connected to the pilot pipeline 33 and the rod side oil. It becomes an open position (d) which connects the chambers 10E and 10F. As a result, the pilot pressure in the pilot line 33 is directly supplied to the rod side oil chambers 10E and 10F of the hoist cylinder 10, and the hoist cylinder 10 has a thrust F (contraction force F) in a direction to reduce the rod 10C. Occurs. As a result, the vessel 5 can be pressed against the vehicle body 4 by the hoist cylinder 10.

  In the embodiment and the modification described above, the case where the control valve device 17 is configured using the first and second directional control valves 22 and 23 has been described as an example. However, the present invention is not limited to this, and the control valve device may be configured by using, for example, one (single) directional control valve at 4 ports and 4 positions.

  In the embodiment and the modification described above, the case where the two-stage hoist cylinder 10 is used has been described as an example. However, the present invention is not limited to this, and for example, a multi-stage hoist cylinder (hydraulic cylinder) of three or more stages or a single-stage hoist cylinder (hydraulic cylinder) may be used. For example, in the case of a single-stage hoist cylinder, it can be constituted by a single cylinder (cylinder portion), a rod, and a piston that defines the inside of the cylinder as a rod-side oil chamber and a bottom-side oil chamber.

  Furthermore, in embodiment and the modification which were mentioned above, the rear-wheel drive type dump truck 1 was mentioned as an example and demonstrated as a transport vehicle. However, the present invention is not limited to this, and may be applied to, for example, a front-wheel drive type or a four-wheel drive type dump truck that drives both front and rear wheels. You may apply to a transport vehicle. Furthermore, the present invention can also be applied to a crawler type transport vehicle.

1 Dump truck (transportation vehicle)
4 Car body 5 Vessel 10 Hoist cylinder 10A Outer cylinder (cylinder)
10B Inner cylinder part 10C Rod 10D Piston 10E, 10F Rod side oil chamber 10G Bottom side oil chamber 11 Main hydraulic pump (hydraulic pump)
DESCRIPTION OF SYMBOLS 12 Hydraulic oil tank 15 Rod side main pipe 16 Bottom side main pipe 17 Control valve apparatus 22 1st direction control valve 22B Hydraulic pilot part 23 2nd direction control valve 26A 1st detour oil path (tank pipe line)
29A Relief valve 41 Switching valve 42, 51 Connection line 43 Restriction

Claims (3)

A vehicle body that can travel,
A vessel on the vehicle body that can be tilted upward and downward with the rear side as a fulcrum and on which a load is loaded;
A hoist cylinder provided between the vessel and the vehicle body and tilting the vessel upward and downward about the fulcrum by extending or contracting a rod;
A hydraulic pump;
A directional control valve provided between the hydraulic pump and the hoist cylinder;
A rod-side main pipe connecting the directional control valve and the rod-side oil chamber of the hoist cylinder;
A bottom main line connecting the directional control valve and the bottom oil chamber of the hoist cylinder;
A pilot line for supplying pilot pressure to the directional control valve,
The directional control valve includes a raised position (R) for tilting the vessel upward by the hoist cylinder, a lowered position (L) for reducing the hoist cylinder and tilting the vessel downward, and the vessel side In the transport vehicle having a plurality of switching positions consisting of a floating position (F) where the hoist cylinder is reduced by its own weight to allow the vessel to fall by its own weight and a neutral position (N) for holding the vessel,
A connection pipe connecting the pilot pipe and the rod side main pipe or the rod side oil chamber;
When the directional control valve is provided in the middle of the connecting pipe and is in the floating position (F), the pilot pipe and the rod side main pipe or the rod side oil chamber are opened to communicate with each other, and the direction control is performed. When the valve is in a position other than the floating position (F), a switching valve that is in a closed position for blocking communication between the pilot pipe line and the rod side main pipe line or the rod side oil chamber ,
The directional control valve includes a first directional control valve and a second directional control valve connected in parallel between the hydraulic pump and the hoist cylinder.
The first directional control valve is configured to switch to any one of the neutral position (N), the raised position (R), and the floating position (F),
The second directional control valve is configured to switch to any one of the neutral position (N), the raised position (R), and the lowered position (L),
The switching valve, by a portion of the first pilot pressure supplied to the directional control valve to the hydraulic pilot portion for switching the floated position (F) is supplied, and an that a drop-in replacement switching configuration to said open position A transport vehicle characterized by that.   The transport according to claim 1, wherein a tank pipe connecting between the rod side main pipe and the hydraulic oil tank is provided with a relief valve for relieving excess pressure in the rod side main pipe to the hydraulic oil tank. vehicle.   2. The transport vehicle according to claim 1, wherein the connection pipe is provided with a throttle that reduces a flow area of the connection pipe between the switching valve and the rod-side main pipe or the rod-side oil chamber. .

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