JP2019048522A - Transport vehicle - Google Patents

Abstract

To improve workability of a traction work of a failed vehicle using a tractor.SOLUTION: A dump truck 1 includes a vehicle body 2 having a fron wheel 3 and a rear wheel 4, an engine 7 mounted on the vehicle body 2, a hydraulic pump 10 driven by the engine 7, a cargo bed 5 arranged on the vehicle body 2 so as to be raised and lowered, a hydraulic actuator which is mounted on the vehicle body 2 and is operated by pressure oil supplied from the hydraulic pump 10, an accumulator 43 which accumulates the pressure oil from the hydraulic pump 10, and a controller 48 which performs bleed-down control for emitting the pressure oil accumulated in the accumulator 43 to a tank 11 when a certain time passes after the engine 7 stops. A bleed-down control inhibiting switch 50 inhibits the bleed-down control by the controller 48 when the engine 7 stops.SELECTED DRAWING: Figure 2

Description

  The present invention relates to a transport vehicle suitably used to transport, for example, crushed stone mined in a mine.

  Generally, a dump truck as a representative example of a large transport vehicle is suitably used to transport crushed stone or soil excavated in a mine or the like. The dump truck includes a self-propelled vehicle body having wheels, an engine (motor) mounted on the vehicle body, a generator and a hydraulic pump driven by the engine, and a loading platform (vessel) provided on the vehicle body so as to be able to move up and down. Is equipped.

  In addition, dump trucks include negative parking brake devices that apply braking force to the wheels when parking, steering cylinders for steering the left and right front wheels, and hoist cylinders that raise the front side of the platform against the vehicle body. A hydraulic actuator is mounted.

  The parking brake device releases braking on the wheels and enables the dump truck to travel by supplying pressure oil (brake release pressure) from the hydraulic pump. The steering cylinder controls the traveling direction of the dump truck by steering the left and right front wheels, for example, in accordance with the steering wheel operation of the operator. The hoist cylinder stretches the front side of the loading platform relative to the vehicle body by expanding and contracting between the vehicle body and the loading platform, and loads and unloads the loading platform on the loading platform.

  Here, the dump truck is mounted with an accumulator for storing pressure oil discharged from the hydraulic pump, and the accumulator constitutes a temporary hydraulic source for the hydraulic actuator. A dump truck provided with an accumulator is usually provided with a bleed-down device. This bleed-down device releases the pressure (pressure oil) stored in the accumulator to a tank when a predetermined time has elapsed after the engine of the dump truck is stopped (see Patent Document 1).

JP, 2009-264456, A

  By the way, when a certain kind of abnormality occurs in the dump truck and the dump truck becomes inoperable, it is necessary to tow the dump truck by a tow truck and move it to a desired repair place or the like. When the engine of the dump truck is stopped, the hydraulic pump is not driven, so the brake release pressure can not be supplied to the parking brake device, and the parking brake device can not be released. In addition, since the supply of pressure oil to the steering cylinder is stopped, it is not possible to steer the left and right front wheels of the dump truck to be pulled.

  Therefore, when moving a dump truck that has become inoperable to a repair site or the like by a tow truck, the parking brake device is supplied by supplying hydraulic fluid from the hydraulic source mounted on the tow truck to each hydraulic actuator of the dump truck. It is necessary to release the brakes and steer the left and right front wheels of the dump truck to be pulled by the steering cylinder.

  In this way, when the dump truck stops driving and becomes unable to travel, the hydraulic source mounted on the tow truck and the hydraulic actuator mounted on the dump truck are connected using a hydraulic hose or the like. It is necessary to supply pressure oil to each hydraulic actuator of the dump truck from the hydraulic source of the tractor. As a result, it is necessary to provide the traction vehicle with a hydraulic pressure source that can supply pressure oil to the hydraulic actuator mounted on the traction vehicle and the hydraulic actuator mounted on the broken truck (dump truck). Has the problem of becoming larger. In addition, a large-scale operation of connecting the hydraulic source of the towing vehicle to the hydraulic actuator of the defective vehicle is required, and there is a possibility that oil may leak from the connection. For this reason, in order to move a dump truck to a desired repair place with a tow truck, much time is needed, and there exists a problem that the workability of a tow operation will fall.

  The present invention has been made in view of the above-described problems of the prior art, and an object of the present invention is to provide a transport vehicle capable of enhancing the operability of a pulling operation using a tow vehicle.

  The present invention operates with a self-propelled vehicle body having wheels, a motor mounted on the vehicle body, a hydraulic pump driven by the motor, and pressure oil mounted on the vehicle body and supplied from the hydraulic pump A hydraulic actuator, an accumulator for accumulating pressure oil supplied from the hydraulic pump, and a valve-closing position provided in the middle of an oil passage communicating between the accumulator and the tank and holding the pressure oil accumulated in the accumulator And a valve opening position to be discharged to the tank, and the pressure valve stored in the accumulator is switched to the valve opening position by switching the switching valve to the valve opening position when the motor stops and the predetermined time passes. It applies to the conveyance vehicle provided with the controller which performs the bleed down control discharged | emitted to a tank.

  A feature of the present invention is that a bleed-down control prohibiting device is provided that prohibits bleed-down control by the controller when the motor stops.

  According to the present invention, by prohibiting the bleed-down control by the controller by the bleed-down control prohibiting device, the pressure oil can be stored in the accumulator even after the motor has stopped and a predetermined time has elapsed. Therefore, when the tow truck is used to tow the transport vehicle, the pressure oil in the accumulator can be used to drive the hydraulic actuator. Therefore, between the hydraulic source mounted on the tow truck and the hydraulic actuator on the transport vehicle It is possible to eliminate the need for connecting work, and to improve the tow work efficiency.

It is a front view showing a dump truck as a transport vehicle according to an embodiment of the present invention. FIG. 2 is a hydraulic circuit diagram showing a system for controlling a hydraulic actuator mounted on a dump truck. It is a flowchart which shows the work procedure when towing a dump truck using a tow truck.

  Hereinafter, a dump truck according to the present invention will be described in detail with reference to FIGS. 1 to 3.

  The dump truck 1 is for transporting a material such as crushed stone or soil mined in a mine or the like. The dump truck 1 is provided on the rear upper side of the vehicle body 2 with the vehicle body (main frame) 2 having a robust frame structure, the left and right front wheels 3 and the left and right rear wheels 4 provided under the vehicle body 2 And a loading platform (vessel) 5 on which a load such as earth and sand is loaded. The left and right front wheels 3 constitute steered wheels, and when the operator of the dump truck 1 operates a steering handle 35 described later, the steering operation is performed along with the telescopic operation of the left and right steering cylinders 29, 30 described later. Ru. The left and right rear wheels 4 constitute drive wheels. A deck portion 2A which is a flat floor plate is provided on the front side of the vehicle body 2, and an engine 7 as a prime mover is mounted below the deck portion 2A. The engine 7 drives a hydraulic pump 10 described later.

  The loading platform 5 is mounted on a bracket 2B provided at the rear of the vehicle body 2 so as to be able to tilt (relief) using a hinge pin 5A, and a portion of the lower portion of the loading platform 5 in front of the hinge pin 5A and the vehicle body 2 A hoist cylinder 8 is provided which extends upward and downward. Accordingly, the front side of the loading platform 5 is configured to tilt upward and downward with the hinge pin 5A as a fulcrum in accordance with the expansion and contraction operation of the hoist cylinder 8, and to discharge the transported material. On the front side of the loading platform 5, a collar 5B is integrally provided to cover a cab 9 described later from the upper side.

  The cab 9 is provided on the front side of the vehicle body 2 so as to be located below the flange 5 </ b> B of the loading platform 5. That is, the cab 9 is provided on the deck portion 2A disposed on the front side of the vehicle body 2. The cab 9 forms a cab for the operator (driver) of the dump truck 1 to get on and off, and inside the cab 9 a driver's seat, an accelerator pedal (neither is shown), a hoist lever device 28 described later, a steering A steering wheel 35, a bleed down control prohibition switch 50, an engine speed setting device 51 and the like are arranged.

  The dump truck 1 also includes a hydraulic pump 10, a control valve device 18, left and right steering cylinders 29, 30, a steering operation valve 32, a parking brake device 37, a parking brake valve 42, an accumulator 43, and bleed down switching. A valve 46, a controller 48 and the like are mounted. The controller 48 controls the ups and downs movement (lifting / lowering) of the bed 5 by the hoist cylinder 8, the steering of the front wheel 3 of the dump truck 1 by the left and right steering cylinders 29 and 30, the bleed down operation by the bleed down switching valve 46, and the like.

  Next, a system for controlling various hydraulic actuators mounted on the dump truck 1 will be described with reference to FIG.

  The variable displacement hydraulic pump 10 constitutes a hydraulic pressure source together with the tank 11. A first supply pipe line 13 and a second supply pipe line 14 are connected to the discharge side of the hydraulic pump 10 via the direction control valve 12. The directional control valve 12 is switched to any one of the first position (A), the second position (B), and the third position (C). Further, the tank 11 is connected to a first return line 15 and a second return line 16.

  The bottom oil chamber 8A of each hoist cylinder 8 is connected to a pair of hydraulic pipelines 17A, and the rod oil chamber 8B of each hoist cylinder 8 is connected to a pair of hydraulic pipelines 17B. The control valve device 18 is provided between an oil pressure source consisting of the oil pressure pump 10 and the tank 11 and each hoist cylinder 8. The control valve device 18 is configured to include a high pressure side pipe line 19, a low pressure side pipe line 20, a bypass pipe line 21, a first direction control valve 22, and a second direction control valve 23.

  The first directional control valve 22 is switched from the neutral position (N) to the raised position (R) or the floating position (F). On the other hand, the second directional control valve 23 is switched from the neutral position (N) to the raising position (R) or the lowering position (L).

  Between the hydraulic lines 17A, 17B and the low pressure side pipe 20, check valves 24A, 24B for make-up and relief valves 25A, 25B are provided in a state of bypassing the first direction control valve 22, respectively. There is. Check valves 26A and 26B for make-up are provided between the hydraulic lines 17A and 17B and the low pressure side pipe 20 in a state of bypassing the second direction control valve 23, respectively. Further, a relief valve 27 is provided between the high pressure side pipe line 19 and the low pressure side pipe line 20.

  The hoist lever device 28 is provided in the cab 9. The hoist lever device 28 is constituted by, for example, an electric lever device, and manually operated by an operator in the cab 9 for tilting operation. Then, the hoist lever device 28 lowers the front side of the cargo bed 5 by its own weight, with a holding position for holding the cargo bed 5 in a stopped position, a raising position for raising the front side of the cargo bed 5, a lowering position for lowering the front side of the cargo bed 5, and The tilting operation is performed to any position with the floating position. When the hoist lever device 28 is switched to any one of the holding position, the raising position, the lowering position, and the floating position, a signal corresponding to the switching position is output to the controller 48. Thereby, for example, the controller 48 is directed from the pilot pressure generator (not shown) to the hydraulic pilot parts 22A and 22B of the first directional control valve 22 and the hydraulic pilot parts 23A and 23B of the second directional control valve 23. The pilot pressure is output, and the first and second directional control valves 22 and 23 are set to the neutral position (N), the raising position (R), the lowering position (L) and the floating position according to the switching position of the hoist lever device 28 Switch to (F). The hoist cylinder 8 receives supply of pressure oil according to the switching position of the hoist lever device 28 to raise and lower the loading platform 5.

  Left and right steering cylinders 29 and 30 as hydraulic actuators are provided on the left and right front wheels 3 of the vehicle body 2. The left and right steering cylinders 29, 30 expand and contract in response to the operation of the steering wheel 35, thereby steering the left and right front wheels 3. Here, the left steering cylinder 29 has a bottom side oil chamber 29A and a rod side oil chamber 29B, and the right steering cylinder 30 has a bottom side oil chamber 30A and a rod side oil chamber 30B. The bottom side oil chamber 29A of the left steering cylinder 29 and the rod side oil chamber 30B of the right steering cylinder 30 are connected via a hydraulic pipeline 31A. The bottom side oil chamber 30A of the right steering cylinder 30 and the rod side oil chamber 29B of the left steering cylinder 29 are connected via a hydraulic pipeline 31B. The hydraulic lines 31A and 31B are connected to the high pressure side conduit 33 and the low pressure side conduit 34 via the steering operation valve 32.

  The steering wheel 35 is provided in the cab 9. The steering handle 35 controls the traveling direction of the dump truck 1 by being turned by the operator in the left and right directions. A hydraulic motor 36 is connected to the handle shaft 35A of the steering handle 35, and the operation force on the steering handle 35 is reduced by the rotation of the hydraulic motor 33.

  The parking brake device 37 is provided, for example, in the vicinity of the electric motor 6 that drives the left and right rear wheels 4. The parking brake device 37 includes a brake cylinder 38 and a brake pad 39 provided on the brake cylinder 38. The parking brake device 37 parks the dump truck 1 by pressing the brake pad 39 against a disk 40 that rotates integrally with the electric motor 6. The braking force is applied to the left and right rear wheels 4 from time to time.

  The parking brake valve 42 is provided between a hydraulic pressure source consisting of the hydraulic pump 10 and the tank 11 and the brake pipeline 41. When the parking brake valve 42 is in the braking position (D), the dump truck 1 holds the parking state by applying a braking force to the left and right rear wheels 4. On the other hand, when the parking brake valve 42 is switched to the brake release position (E), the dump truck 1 is shifted to the traveling state by releasing the braking force on the left and right rear wheels 4.

  The accumulator 43 is connected to the first supply line 13 and the high pressure side line 33. The accumulator 43 accumulates the pressure oil discharged from the hydraulic pump 10, and constitutes a temporary hydraulic source for hydraulic actuators such as the respective hoist cylinders 8, the left and right steering cylinders 29, 30, the parking brake device 37 and the like. That is, when pressure oil is not supplied from the hydraulic pump 10 to the first and second supply pipelines 13 and 14 due to a failure of the hydraulic pump 10 or the like, the pressure oil accumulated in the accumulator 43 corresponds to each hoist cylinder 8, left , Right steering cylinders 29, 30, and parking brake device 37. A relief valve 44 is provided between the high pressure side conduit 33 and the first return conduit 15. Further, a relief valve 45 is provided between the first supply line 13 and the first return line 15.

  A bleed-down switching valve 46 as a switching valve is provided in the middle of the bleed-down pipeline 47, which is an oil passage connecting the accumulator 43 and the tank 11. The bleed-down switching valve 46 is, for example, an electromagnetic pilot directional control valve with two ports and two positions, and the valve closing position (H) and the valve opening position (G) according to the signal supplied from the controller 48 to the electromagnetic pilot unit 46A. Switch to When the bleed down switching valve 46 is in the valve closing position (H), pressure oil is held in the accumulator 43. On the other hand, when the bleed down switching valve 46 is switched to the valve opening position (G), the pressure oil in the accumulator 43 is transferred to the bleed down line 47, the bleed down switching valve 46, the low pressure side pipe 34, and the first return. It is discharged to the tank 11 through the pipe line 15.

  The controller 48 is accumulated in the control valve device 18 (first and second directional control valves 22 and 23) for controlling the operation of the hoist cylinder 8, the parking brake valve 42 for controlling the operation of the parking brake device 37, and the accumulator 43. It controls the bleed down switching valve 46 and the like that control the retention and discharge of the pressure oil. The input side of the controller 48 is connected to a hoisting lever device 28, a parking brake switch 49 for instructing the operation of the parking brake device 37, an engine speed setting device 51 described later, and the like.

  The controller 48 controls the first and second directional control valves 22 and 23 in the neutral position (N), the raising position (R), the lowering position (L) and the floating position (F) according to the signal from the hoist lever device 28 Control to switch to. Further, the controller 48 performs control to switch the parking brake valve 42 to the brake position (D) or the brake release position (E) in accordance with a signal from the parking brake switch 49. Furthermore, the controller 48 outputs a signal to the electromagnetic pilot section 46A of the bleed down switching valve 46 to switch to the valve opening position (G) when the engine 7 is stopped and a predetermined time has elapsed, thereby accumulating pressure in the accumulator 43. Control (bleed-down control) of discharging the pressure oil to the tank 11 is performed.

  A bleed-down control inhibiting switch 50 as a bleed-down control inhibiting device is provided in the middle of a cable electrically connecting the controller 48 and the electromagnetic pilot unit 46A of the bleed-down switching valve 46. The bleed down control prohibition switch 50 is disposed, for example, in the cab 9 and operated by the operator. Here, bleed-down control prohibition switch 50 normally electrically connects between controller 48 and electromagnetic pilot unit 46A, and when operated by the operator, it electrically connects between controller 48 and electromagnetic pilot unit 46A. Shut off. That is, when the bleed down control prohibition switch 50 is operated, the signal from the controller 48 is not supplied to the electromagnetic pilot unit 46A of the bleed down switching valve 46 even when the engine 7 is stopped and a predetermined time has elapsed. The pressure oil is held within 43.

  An engine speed setting device 51 as a speed setting device is provided in the cab 9. The engine rotation number setting device 51 is operated by an operator in the cab 9 to set the rotation number of the engine 7 in two stages of a predetermined low rotation number and a high rotation number. The rotational speed set by the engine rotational speed setting device 51 is input to the controller 48, and the controller 48 controls the rotational speed of the engine 7 according to the set rotational speed.

  Here, when the dump truck 1 is traveling, the number of rotations of the engine 7 is variably set according to the amount of operation of an accelerator pedal (not shown) disposed in the cab 9. On the other hand, when it is an abnormality that the dump truck 1 can not travel by itself due to, for example, a failure of the electric motor 6, it is necessary to use the tow truck (not shown) to pull the dump truck 1 and move it to a desired repair location. In this case, when the engine 7 is operable, it is necessary to supply pressure oil from the hydraulic pump 10 to the left and right steering cylinders 29, 30 in order to steer the front wheel 3 of the dump truck 1 to be pulled. . When the operator operates the accelerator pedal to set the number of revolutions of the engine 7 at the time of this pulling operation, it becomes a complicated operation involving fatigue for the operator. For this reason, when the engine 7 can be operated at the time of pulling work of the dump truck 1, instead of the operation of the accelerator pedal by the operator, the engine speed setting device 51 sets the engine speed to a low speed and a high speed. It can be set in two stages.

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

  When an operator who gets in the cab 9 starts the engine 7, the hydraulic pump 10 is rotationally driven, and the hydraulic oil in the tank 11 is sucked and discharged as pressure oil. When the direction control valve 12 is at the first position (A), the pressure oil from the hydraulic pump 10 is supplied to the accumulator 43 through the first supply line 13, and the pressure oil is accumulated in the accumulator 43.

  Next, the operator in the cab 9 operates the parking brake switch 49 to release the braking by the parking brake device 37. Thereby, a signal is supplied from the controller 48 to the parking brake valve 42, and the parking brake valve 42 is switched from the brake position (D) to the brake release position (E). Therefore, the pressure oil (brake release pressure) from the hydraulic pump 10 is supplied to the brake cylinder 38, and the brake pad 39 separates from the disc 40. As a result, the braking by the parking brake device 37 is released, and the left and right rear wheels 4 are rotationally driven according to the stepping operation of the accelerator pedal (not shown), whereby the dump truck 1 can be made to travel.

  In this state, when the operator in the cab 9 rotates the steering wheel 35, the steering operation valve 32 is switched from the neutral position (N ') to either the left or right steering position (L') or (R '). Be At this time, the pressure oil from the hydraulic pump 10 is supplied to the left and right steering cylinders 29 and 30 via the steering operation valve 32 to extend or reduce them. Thus, the left and right front wheels 3 of the dump truck 1 are steered in accordance with the rotation operation of the steering handle 35, and the dump truck 1 can travel freely by the operation of the operator.

  Next, when the dump truck 1 is incapable of traveling for some reason, it is necessary to tow the dump truck 1 by the tow truck and move it to a desired repair place. The operation procedure in the case where the dump truck 1 can not be driven will be described with reference to FIG.

  When towing the dump truck 1 that has become inoperable, it is necessary to supply pressure oil for releasing the brake to the brake cylinder 38 in order to release the braking force to the rear wheel 4 by the parking brake device 37. Further, in order to steer the front wheel 3 of the dump truck 1 to be pulled, it is necessary to supply operating pressure oil to the left and right steering cylinders 29, 30 according to the operation of the steering handle 35. Furthermore, when a load is loaded on the loading platform 5, it is necessary to supply hydraulic oil for operation to the hoist cylinder 8 in order to discharge the load from the loading platform 5 to reduce the weight of the dump truck 1. .

  Here, the reasons why the dump truck 1 can not travel are roughly classified into, for example, the case where the engine 7 fails and can not operate, and the case where the engine 7 can operate but the traveling electric motor 6 breaks down. When it becomes impossible to travel due to the failure of the electric motor 6, the hydraulic pump 10 is driven by the engine 7 to lift the pressure oil discharged from the hydraulic pump 10 to the hoist cylinder 8, the steering cylinders 29, 30 on the left and right, A hydraulic actuator such as the brake cylinder 38 can be supplied.

  For this reason, when a tow truck (not shown) is connected to the dump truck 1 to perform a pulling operation, it is determined in step 1 of FIG. 3 whether or not the engine 7 can be operated. If it is determined in step 1 that the result is "YES", the hydraulic pump 10 can be driven by the engine 7, so the process proceeds to step 2. In step 2, the operator in the cab 9 sets the rotational speed of the engine 7 to the high rotational speed or the low rotational speed by the engine speed setting device 51.

  Here, when the dump truck 1 is towed, pressure oil from the hydraulic pump 10 needs to be continuously supplied to the left and right steering cylinders 29, 30 in order to steer the front wheel 3 of the dump truck 1 to be towed. However, setting the number of revolutions of the engine 7 by operating the accelerator pedal (not shown) by the operator is a complicated and troublesome task for the operator. Therefore, by operating the engine speed setting device 51 in step 2, it is possible to set the speed of the engine 7 without operating the accelerator pedal.

  In the following step 3, it is determined by the engine speed setting device 51 whether or not the speed of the engine 7 is set to a high speed. When it is judged as "NO" at Step 3, since the number of revolutions of the engine 7 is set to the low number of revolutions, the discharge amount of the pressure oil from the hydraulic pump 10 decreases. Therefore, in the subsequent step 4, the brake release operation by the brake cylinder 38, the steering of the front wheel 3 by the left and right steering cylinders 29 and 30, and the raising and lowering operation of the loading platform 5 by the hoist cylinder 8 can be performed at low speed.

  On the other hand, when it is judged as "YES" at Step 3, since the number of rotations of the engine 7 is set to the high number of rotations, the discharge amount of the pressure oil from the hydraulic pump 10 increases. For this reason, in the subsequent step 5, the brake release operation by the brake cylinder 38, the steering of the front wheel 3 by the left and right steering cylinders 29 and 30, and the raising and lowering operation of the bed 5 by the hoist cylinder 8 can be performed at high speed.

  Next, if it is determined "NO" in step 1, that is, if the hydraulic pump 10 can not be driven due to the failure of the engine 7, the process proceeds to step 6. In step 6, it is determined whether to receive the supply of pressure oil from a hydraulic pressure source (not shown) mounted on the tractor. If it is determined "YES" in step 6, the process proceeds to step 7, and the brake cylinder 38, the left and right steering cylinders 29 and 30, and the hoist cylinder 8 are operated using pressure oil supplied from the tractor. The release of braking by the parking brake device 37, the steering of the left and right front wheels 3, and the raising and lowering operation of the loading space 5 can be performed.

  If "NO" is determined in the step 6, that is, if it is determined that the pressure oil supply from the tractor is not received, the process proceeds to the step 8. In step 8, it is determined whether or not sufficient pressure oil is accumulated in the accumulator 43 of the dump truck 1. If "NO" in the step 8, the pressure oil is not accumulated in the accumulator 43, so the process returns to the step 6. On the other hand, if “YES” is determined in the step 8, the process proceeds to the step 9.

  In step 9, it is determined whether the operator has operated the bleed-down control prohibition switch 50 or not. If “NO” is determined in the step 9, the bleed down control prohibition switch 50 is not operated, and the electromagnetic pilot unit 46A of the bleed down switching valve 46 and the controller 48 are electrically connected. . For this reason, when a predetermined time passes after the dump truck 1 becomes inoperable and the operation of the engine 7 is stopped, a signal for commanding bleed-down control to the bleed-down switching valve 46 is supplied from the controller 48.

  As a result, the bleed down switching valve 46 is switched to the valve opening position (G), and the pressure oil accumulated in the accumulator 43 is discharged to the tank 11. Accordingly, in the subsequent step 10, the parking brake device 37 is actuated to apply the braking force to the rear wheel 4, and the steering of the front wheel 3 by the left and right steering cylinders 29, 30 and the bed 5 by the hoist cylinder 8. The relief operation is stopped. In this state, since the dump truck 1 can not be towed, the dump truck 1 can be towed by the tractor, for example, by returning to step 6 and receiving the supply of pressure oil from the hydraulic source of the tractor.

  On the other hand, if "YES" is determined in the step 9, that is, if the operator operates the bleed down control prohibition switch 50, the electromagnetic pilot unit 46A of the bleed down switching valve 46 and the controller 48 are electrically disconnected. Be done. Therefore, bleed-down control is not performed even if a predetermined time passes after the dump truck 1 becomes inoperable and the operation of the engine 7 is stopped, and sufficient pressure oil can be held in the accumulator 43. .

  Therefore, in the subsequent step 11, the pressure release oil from the accumulator 43 is used to perform the brake release operation by the brake cylinder 38, the steering of the front wheel 3 by the left and right steering cylinders 29 and 30, and the hoisting operation of the bed 5 by the hoist cylinder 8. be able to. As described above, by using the pressure oil accumulated in the accumulator 43, the work of connecting the hydraulic source mounted on the tow truck and the hydraulic actuators of the dump truck 1 can be made unnecessary, and from the connection portion It can reduce the risk of oil leaks. As a result, the tow operation of the dump truck 1 by the tow truck can be performed quickly and smoothly, and the workability can be enhanced.

  Thus, the dump truck 1 according to the present embodiment is provided with a bleed down control prohibiting switch 50 for inhibiting the bleed down control by the controller 48 when the engine 7 is stopped. Therefore, even when the engine 7 is stopped and a certain time period has elapsed by prohibiting the bleed-down control by the controller 48 by the bleed-down control prohibit switch 50 when the dump truck 1 can not travel due to any cause. The accumulator 43 can store pressure oil.

  Therefore, when the dump truck 1 is towed using a tow truck, the hydraulic oil in the accumulator 43 is used to drive the hydraulic actuators such as the brake cylinder 38, the left and right steering cylinders 29, 30, the hoist cylinder 8, etc. Can. As a result, the work of connecting the hydraulic pressure source mounted on the tow truck and the hydraulic actuator of the dump truck 1 can be eliminated, and the workability at the time of traction can be improved.

  In addition, the dump truck 1 is provided with an engine rotation number setting device 51 that sets the rotation number of the engine 7 at the time of an abnormality that the vehicle body 2 can not travel freely. Therefore, when the hydraulic pump 10 can be driven by the engine 7 when the dump truck 1 is towed, the rotational speed of the engine 7 is set by the operation of the engine rotational speed setting device 51 and supplied from the hydraulic pump 10 to the hydraulic actuator. The pressure oil flow rate can be adjusted. As a result, the operation of setting the number of rotations of the engine 7 by the operator's depression operation of the accelerator pedal can be eliminated, and the burden on the operator can be alleviated.

  In the embodiment, a bleed-down control prohibiting switch 50 provided in the middle of a cable connecting the controller 48 and the electromagnetic pilot portion 46A of the bleed-down switching valve 46 is used as the bleed-down control prohibiting device. A case where the controller 48 and the electromagnetic pilot unit 46A are electrically disconnected by operating the bleed down control prohibition switch 50 is illustrated.

  However, the present invention is not limited to this. For example, when the bleed-down control prohibition switch is connected to the input side of the controller 48 and this bleed-down control prohibition switch is operated, the controller 48 causes the electromagnetic of the bleed-down switching valve 46 The output of the signal to the pilot unit 46A may be inhibited.

  Further, in the embodiment, an engine rotation number setting device 51 which sets the number of rotations of the engine 7 to two stages of low rotation number and high rotation number is illustrated as the rotation number setting device. However, the present invention is not limited to this. For example, the number of revolutions of the engine 7 may be set to three or more stages.

  Further, in the embodiment, the case where the parking brake device 37 for applying the braking force to the rear wheel 4 when the dump truck 1 is parked is provided with one brake cylinder 38 is exemplified. However, the present invention is not limited to this. For example, two or more brake cylinders may be provided.

  Furthermore, in the embodiment, the engine 7 is illustrated as the prime mover, but the present invention is not limited to this, and for example, an electric motor may be used as the prime mover.

2 body 5 bed 7 engine (motor)
10 hydraulic pump 11 tank 29 left steering cylinder (hydraulic actuator)
30 Right steering cylinder (hydraulic actuator)
37 Parking brake system (hydraulic actuator)
43 Accumulator 46 Bleed-down switching valve (switching valve)
47 bleed down line (oil line)
48 Controller 50 Bleed-down control prohibition switch (Breed-down control prohibition device)
51 Engine speed setting device (speed setting device)

Claims (5)

A self-propelled car body having wheels,
A motor mounted on the vehicle body,
A hydraulic pump driven by the motor;
A hydraulic actuator mounted on the vehicle body and operated by pressure oil supplied from the hydraulic pump;
An accumulator for accumulating pressure oil supplied from the hydraulic pump;
A switching valve provided in the middle of an oil passage communicating between the accumulator and the tank and switching between a valve closing position for holding the pressure oil accumulated in the accumulator and a valve opening position for discharging the oil to the tank;
A transport vehicle comprising: a controller performing bleed-down control to switch the switching valve to the valve opening position and discharge the pressure oil accumulated in the accumulator to the tank when the motor stops and a predetermined time elapses In
A conveyance vehicle characterized by comprising a bleed-down control inhibiting device for inhibiting bleed-down control by the controller when the motor stops.   The transport vehicle according to claim 1, wherein the vehicle body is provided with a rotation speed setting device for setting a rotation speed of the motor when the vehicle body can not travel by itself. The hydraulic actuator is a steering cylinder for steering the wheel,
The pressure oil from the accumulator is supplied to the steering cylinder when the motor stops by prohibiting the bleed down control by the controller by the bleed down control inhibiting device. Transport vehicle. The hydraulic actuator is a negative parking brake device that normally applies a braking force to the vehicle and releases the braking force by the supply of pressure oil.
The pressure oil from the accumulator is supplied to the parking brake device when the motor stops by prohibiting the bleed-down control by the controller by the bleed-down control prohibiting device. Transport vehicle described. The vehicle body is provided with a rack which can be undulated to load and discharge luggage.
The hydraulic actuator is a hoist cylinder that raises and lowers the bed.
The pressure oil from the accumulator is supplied to the hoist cylinder when the motor stops by prohibiting the bleed down control by the controller by the bleed down control inhibiting device. Transport vehicle.

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