JP2007177798A - Hydraulic traveling device of working vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To effectively cool a hydraulic oil while maintaining traveling performance requested during high-speed traveling without remarkably increasing the output of a prime mover, in a hydraulic traveling device of a working vehicle. <P>SOLUTION: The hydraulic oil discharged from a hydraulic pump 3 for working flows into an oil cooler 8. The hydraulic oil is returned into a tank T after being cooled by the oil cooler 8 while utilizing the traveling air of the work vehicle. The hydraulic oil in the tank T is fed into a hydraulic motor 22 for traveling by main pumps 4, 16 for traveling. The traveling speed is detected by a vehicle speed sensor 35. The higher the traveling speed is, the more the pump capacity of the hydraulic pump 3 is reduced to reduce the load on the prime mover 1 for cooling the hydraulic oil by the oil cooler 8. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an apparatus for hydraulically driving a work vehicle such as a self-propelled crane.

  In general, when a working vehicle such as a self-propelled crane is driven by hydraulic pressure, the driving load is high, so the temperature of the hydraulic oil is likely to rise and the equipment is likely to overheat. is there. In particular, in the case of a hydraulic traveling vehicle with an HST (Hydrostatic Transmission = hydrostatic continuously variable transmission) in which a traveling hydraulic pump and a hydraulic motor are connected by a main line to form a closed circuit, basically the hydraulic fluid is Since the hydraulic fluid is only replaced by the hydraulic fluid drained from the running circuit and the supply of the hydraulic fluid for the drain, the oil temperature rises remarkably. It is important to effectively cool the working oil.

  Conventionally, as a technique for cooling the hydraulic oil for such hydraulic running, Patent Document 1 discloses that the hydraulic oil is blown from the fan to the oil cooler provided in the middle of the working hydraulic circuit. A system is disclosed in which the hydraulic oil is returned to the tank after being cooled, and the hydraulic oil in the tank is appropriately supplied into the traveling hydraulic circuit.

Further, in the document 1, the working hydraulic pump included in the working hydraulic circuit is configured by a variable displacement hydraulic pump, and the oil temperature in the tank is detected, and the higher the oil temperature, the more the variable displacement It describes that control is performed to increase the hydraulic oil flow rate in the oil cooler by increasing the pump capacity of the hydraulic pump.
JP 2004-347083 A

  In general, the driving load for traveling the vehicle tends to increase as the traveling speed increases. Therefore, when the control described in Patent Document 1 is executed, the pump capacity of the working hydraulic pump increases as the traveling speed increases. The flow rate of the hydraulic oil flowing into the cooler will increase, but if the flow rate increases in this way, the pressure loss of the piping in the cooling circuit (that is, the working hydraulic circuit) will increase, and the prime mover will work by that amount. The power consumed to drive the vehicle increases.

  Therefore, when driving at high speed, the required driving speed (for example, the maximum speed) is achieved because the power consumed by the motor is consumed by the pump for cooling even though a large amount of power is required for the driving. There is a risk that it will not be possible to do so, and there is a risk that it will have a significant impact on the driving performance. In addition, when a prime mover larger by one class is adopted in consideration of such circumstances, there arises a disadvantage that the space and cost required for the installation increase.

  In view of such circumstances, the present invention provides a hydraulic traveling device for a work vehicle capable of effectively cooling hydraulic oil while ensuring the traveling capability required during high-speed traveling without significantly increasing the motor output. The purpose is to provide.

As described above, the driving load for traveling tends to increase as the traveling speed of the work vehicle increases. On the other hand, the position where the traveling wind of the work vehicle hits the oil cooler for cooling the hydraulic oil. If this is installed, the traveling wind becomes stronger as the traveling speed becomes higher, and the cooling performance of the oil cooler increases accordingly, so the load of the prime mover for cooling the hydraulic oil in the oil cooler during high-speed traveling is increased. Even if the operation to be reduced is performed, it is possible to maintain effective cooling of the hydraulic oil.

  The present invention has been made from such a viewpoint, and is a hydraulic traveling device that hydraulically travels a work vehicle on which a prime mover and a work machine are mounted, and is driven by the prime mover to supply hydraulic oil to the work machine. A working hydraulic pump to be supplied, an oil cooler that cools the hydraulic oil before the hydraulic oil discharged from the working hydraulic pump returns to the tank, a traveling hydraulic motor for driving the vehicle, A hydraulic circuit that includes a traveling hydraulic pump that is driven by the prime mover and supplies hydraulic oil in the tank to the traveling hydraulic motor, and the oil cooler is provided at a position that receives the traveling wind of the work vehicle. A traveling speed detecting means configured to cool the hydraulic oil using at least the traveling wind, and detecting a traveling speed of the vehicle; The operation control means for controlling the operation of the hydraulic circuit so as to reduce the load on the prime mover for cooling the hydraulic oil in the oil cooler as the traveling speed detected by the speed detection means increases. .

  According to this configuration, when the traveling speed of the work vehicle is low, that is, when the output of the prime mover has a margin while the traveling wind hitting the oil cooler is weak, the oil cooler requires the hydraulic oil to be cooled. While the load of the prime mover is increased to compensate for the shortage of the traveling wind, when the traveling speed of the work vehicle is high, that is, the traveling wind that hits the oil cooler is strong and can maintain sufficient cooling performance, but the engine output is not enough. When it is not, it is possible to reduce the load on the prime mover required for cooling the hydraulic oil in the oil cooler and to secure the power necessary for high speed traveling.

  That is, according to the above-described configuration, it is possible to effectively cool the hydraulic oil regardless of the traveling speed while ensuring the traveling capacity required at the time of high-speed traveling without significantly increasing the motor output.

  Specifically, the working hydraulic pump is constituted by a variable displacement hydraulic pump, and the pumping capacity of the working hydraulic pump is reduced as the running speed detected by the running speed detecting means increases. What was comprised so that it may make it suitable is suitable.

  According to this device, when the traveling speed of the work vehicle is low, the pump capacity of the working hydraulic pump is increased to increase the flow rate of the hydraulic oil flowing into the oil cooler, thereby compensating for the shortage of the traveling wind. When the traveling speed of the vehicle is high, the pump capacity of the work hydraulic pump can be reduced to reduce the load on the prime mover for driving the work hydraulic pump.

  In the present invention, the oil cooler is provided with a fan that gives artificial wind to enhance its cooling performance, and the hydraulic circuit is driven by a fan driving hydraulic motor for driving the fan and the prime mover. A fan driving hydraulic pump that supplies hydraulic oil to the fan driving hydraulic motor, and the fan control hydraulic pump is driven by the prime mover as the running speed detected by the running speed detecting means increases. It is also preferable that the operation state of the hydraulic circuit is controlled so as to reduce the driving load.

  According to this apparatus, when the traveling speed of the work vehicle is low, the driving load of the hydraulic pump for driving the fan by the prime mover is increased to improve the forced cooling performance of the oil cooler by the fan, thereby reducing the shortage of the traveling wind. On the other hand, when the traveling speed of the work vehicle is high, the load of the prime mover for cooling the hydraulic oil can be reduced by reducing the drive load of the fan drive hydraulic pump by the prime mover.

  For example, the fan drive hydraulic motor is composed of a variable displacement hydraulic motor, and the operation control means increases the motor capacity of the variable displacement hydraulic motor as the travel speed detected by the travel speed detection means increases. Assuming that the driving speed is low, when the traveling speed of the work vehicle is low, the motor capacity of the hydraulic motor for driving the fan is reduced to increase the operating speed of the motor and thus the rotational speed of the fan, thereby reducing the shortage of the traveling wind. On the other hand, when the traveling speed of the work vehicle is high, the motor capacity of the fan driving hydraulic motor is increased to reduce the driving pressure, thereby reducing the load for the prime mover to drive the fan driving hydraulic motor. Can be made.

  A variable relief valve is provided in parallel with the fan drive hydraulic motor, and the operation control means reduces the relief pressure of the variable relief valve as the running speed detected by the running speed detecting means increases. If the traveling speed of the work vehicle is low, the relief pressure of the variable relief valve is increased to increase the drive pressure of the fan drive hydraulic motor, thereby increasing the operating speed of the motor and thus the rotational speed of the fan. While compensating for the shortage of the traveling wind, when the traveling speed of the work vehicle is high, the prime mover drives the fan driving hydraulic motor by lowering the relief pressure and decreasing the driving pressure of the fan driving hydraulic motor. Load can be reduced.

  In the present invention, regardless of the specific configuration of the traveling hydraulic circuit for traveling the work vehicle, for example, the traveling hydraulic pump sucks up the hydraulic oil directly from the tank and supplies it directly to the traveling hydraulic motor. However, as the traveling hydraulic pump, a traveling main pump constituting a traveling hydraulic circuit composed of a closed circuit together with the traveling hydraulic motor, and the hydraulic oil in the tank added to the traveling hydraulic circuit composed of the closed circuit. The present invention is particularly effective when the hydraulic oil is less exchanged to the hydraulic circuit for circulating the hydraulic oil in the traveling hydraulic circuit including the closed circuit, such as a device including a hydraulic pump for supplying oil. is there.

  As described above, according to the present invention, the oil cooler is provided at a position for receiving the traveling wind of the work vehicle, and at least the traveling oil is used to cool the hydraulic oil, and the traveling speed of the work vehicle is high. As the oil cooler is designed to reduce the load on the prime mover for cooling the hydraulic oil, the oil cooler operates while ensuring the running ability required at high speed without significantly increasing the output of the prime mover. This has the effect of effectively cooling the oil.

  A first embodiment of the present invention will be described with reference to FIGS.

  FIG. 1A illustrates a self-propelled crane as a work vehicle according to the present invention. The self-propelled crane includes a lower traveling body 40 having traveling wheels 42 and an upper revolving body 44 that is mounted on the lower traveling body 40 so as to be capable of swiveling. A boom 46 can be raised and lowered in the left half of the traveling direction of the upper swing body 44, and a motor cover 48 is provided in the right half, and a cab 50 is installed in front of the motor cover 48. .

  FIG. 2 shows a hydraulic circuit mounted on this hydraulic traveling vehicle.

  This hydraulic circuit includes a working hydraulic pump 3, a traveling main pump 4, and a fan driving hydraulic pump 28 as hydraulic supply sources. These pumps 3, 4, and 28 are connected to the output shaft of the prime mover 1 stored in the prime mover cover 48 via the power distributor 2, and are driven by the operation of the prime mover 1.

  First, a circuit for driving the working hydraulic actuator will be described. This circuit includes the working hydraulic pump 3, and this working hydraulic pump 3 is constituted by a variable displacement hydraulic pump whose tilt angle is operated by the working pump regulator 5.

  The working pump regulator 5 is connected to a pilot pressure source 12 via an electromagnetic proportional valve 11, and a controller 10 is electrically connected to the electromagnetic proportional valve 11. As will be described in detail later, the controller 10 outputs a control signal to the electromagnetic proportional valve 11 to change the secondary pressure of the valve 11, thereby changing the operation stroke of the working pump regulator 5 to change the operating pressure. The working hydraulic pump 3 has a function of controlling the tilt angle and thus the pump capacity.

  The hydraulic fluid discharged from the working hydraulic pump 3 is supplied to the working circuit 6. The work circuit 6 includes a plurality of work hydraulic actuators (not shown) (for example, a hydraulic cylinder, a winch motor, a swing motor, and the like for raising and lowering the boom 46 shown in FIG. 1A). It is driven by hydraulic oil supply from the working hydraulic pump 3.

  The work circuit 6 is connected to a tank T via a tank line 7, and an oil cooler 8 and a check valve 9 are provided in parallel in the tank line 7. The oil cooler 8 cools the hydraulic oil before the hydraulic oil that has passed through the actuator of the work circuit 6 or the actuator control valve provided for the actuator returns to the tank T. The driving wind of the vehicle and the artificial wind by the air suction of the fan 29 are used.

  The oil cooler 8 may be disposed in any position as long as it can be cooled by the vehicle's running wind hitting the main body portion. For example, the positions shown in FIG. 1 (a) and FIG. is there.

  In the example shown in FIG. 5A, the upper surface 48a of the motor cover 48 is a front-declining slope, a louver 52 is provided on the upper surface 48a, and the oil cooler 8 is disposed immediately below the upper surface 48a. The fan 29 is provided directly below the oil cooler 8. Then, the driving wind of the vehicle is guided to the upper surface of the oil cooler 8 by the louver 52, and when the fan 29 is driven, an artificial wind directed from the upper side to the lower side of the oil cooler 8 is formed by the air suction. It has become.

  In the example shown in FIG. 5B, a motor cover 48 and a cab 50 are disposed on the left and right sides of the central boom 46, and an oil cooler 8 is provided in the vicinity of the front surface 48b of the motor cover 48. The fan 29 is provided immediately behind.

  In either case, the running wind generated when the work vehicle travels and the artificial wind generated by the rotation of the fan 29 are applied to the oil cooler 9 so that the hydraulic oil flowing through the oil cooler 9 is cooled. .

  The fan 29 is rotationally driven by a fan driving hydraulic motor 30, and the fan driving hydraulic motor 30 is driven by hydraulic fluid supplied from the fan driving hydraulic pump 28.

On the other hand, in this embodiment, the hydraulic circuit for running the vehicle is constituted by a closed circuit having an HST (Hydrostatic Transmission = hydrostatic continuously variable transmission), and includes a pump circuit A and a motor circuit B. . And the said pump circuit A is installed in the said upper turning body 44 with the said working hydraulic pump 3, the working circuit 6, and its related apparatus, and the motor circuit B is installed in the said lower traveling body 40. FIG.

  The pump circuit A includes a traveling hydraulic pump including the traveling main pump 4 and a replenishing hydraulic pump 16.

  Among these, the traveling main pump 4 is constituted by a bidirectional and variable displacement hydraulic pump, and the tilt angle thereof is operated by the traveling pump regulator 14. The replenishing hydraulic pump 16 is constituted by a fixed displacement hydraulic pump, and plays a role of sucking hydraulic oil from the tank T and replenishing it into the closed circuit.

  In addition, the pump circuit A generates a pressure corresponding to the discharge amount of the electromagnetic switching valve 15 for switching the operating state of the traveling pump regulator 14 and the replenishment hydraulic pump 16 based on the signal from the controller 10. A throttle 17, a pressure reducing valve 18 that reduces the pressure generated by the throttle 17 and sends it to the traveling pump regulator 14 via the electromagnetic switching valve 15, a low pressure relief valve 19, and a maximum circuit pressure are regulated. A pair of overload relief valves 20 and a check valve 21 provided in parallel with each overload relief valve 20 for guiding part of the hydraulic oil from the replenishing hydraulic pump 16 into a closed circuit. .

  The motor circuit B includes a traveling hydraulic motor 22, a flushing valve 23 for discharging excess oil in the closed circuit to the outside of the circuit, a throttle 24 and a flow control valve 25 provided on the downstream side of the flushing valve 23. The output shaft of the traveling hydraulic motor 22 is coupled to a specific traveling wheel 42 via a mechanical traveling speed reducer 31. Then, motor lines 26B and 27B connected to both ports of the traveling hydraulic motor 22 in the motor circuit B, and main lines 26A connected to both ports of the traveling main pump 4 in the hydraulic pump circuit A, 27A is connected to each other via a swivel joint (not shown), thereby forming the above-described closed circuit.

  Between the traveling hydraulic circuit and the tank T, drain pipes 32 and 33 are provided for draining excess hydraulic oil in the hydraulic circuit. Among these, leak oil of the traveling main pump 4 in the pump circuit A and relief oil from the low pressure relief valve 19 flow into the drain pipe 32. In addition, leakage oil from the traveling hydraulic motor 22 in the motor circuit B and oil discharged from the flushing valve 23 flow into the drain line 33. Both drain pipes 32 and 33 join in the middle and are connected to the tank T through the swivel joint.

  In this travel hydraulic circuit, when a shift lever (not shown) is operated, the electromagnetic switching valve 15 is switched by a signal from the controller 10 based on the operation signal, and the oil from the replenishing hydraulic pump 16 is moved to this electromagnetic signal. Tilt of the traveling main pump 4 is increased by being sent to the traveling pump regulator 14 via the switching valve 15. Thereby, the oil discharged from the hydraulic pump 4 is sent to the motor circuit B, the traveling hydraulic motor 22 rotates, and the vehicle travels. During this traveling, the oil leaked from the traveling main pump 4 and the traveling hydraulic motor 22 and the oil discharged from the low pressure relief valve 19 and the flushing valve 23 are returned to the tank T through the drain lines 32 and 33. It will be.

  At this time, the working circuit 6 is stopped in the working hydraulic circuit, but the working hydraulic pump 3 is continuously driven to cool the hydraulic oil in the tank T. That is, the hydraulic oil in the tank T is sucked into the hydraulic pump 3, and the discharged oil flows into the oil cooler 8 after passing through the actuator control valve and the like in the work circuit 6, and is cooled by the oil cooler 8. After that, it is returned to the tank T.

  As described above, the drain oil from the traveling hydraulic circuit to the tank T is cooled by the oil cooler 8 and then re-supplied to the traveling hydraulic circuit by the replenishing hydraulic pump 16, so that the traveling The hydraulic circuit is cooled.

  Further, as a feature of the hydraulic traveling device, a vehicle speed sensor 35 for detecting the traveling speed of the vehicle from the rotational speed of the traveling wheel 42 is provided, and a detection signal of the vehicle speed sensor 35 is input to the controller 10. ing. As shown in FIG. 3, the controller 10 generates a control signal that causes the work pump regulator 5 to reduce the pump capacity of the work hydraulic pump 3 as the traveling speed detected by the vehicle speed sensor 35 increases. It is configured to input to the electromagnetic proportional valve 11.

  According to such a configuration, when the vehicle speed is low, that is, when the traveling load is small and the traveling wind for cooling the oil cooler 8 is small, the pump capacity of the working hydraulic pump 3 is increased to increase the oil cooler. By increasing the hydraulic oil flow rate at 8, the cooling effect is enhanced to compensate for the shortage of the traveling wind, while the traveling wind for cooling the oil cooler 8 is sufficiently received when the vehicle speed is high, that is, traveling. When the load is large, the energy required for high-speed traveling can be ensured by reducing the pump capacity of the working hydraulic pump 3 to reduce the driving load.

  Although FIG. 2 shows a traveling hydraulic circuit composed of a closed circuit, the traveling hydraulic circuit according to the present invention is not limited to this. For example, the traveling hydraulic pump directly sucks hydraulic oil from the tank T. An open type may be directly supplied to the traveling hydraulic motor. However, when the traveling hydraulic circuit is composed of a closed circuit as shown in the figure, there is less travel of hydraulic oil between the traveling hydraulic circuit and the tank T, and more effective hydraulic fluid cooling is required. The present invention is particularly useful.

  Further, the traveling speed detecting means according to the present invention is not limited to the means for detecting the traveling speed from the rotational speed of the traveling wheel 42 as shown in the figure, and may be a means for detecting the traveling speed based on the engine speed, for example. .

  Next, a second embodiment of the present invention will be described with reference to FIGS. In the hydraulic circuit shown in FIG. 4, the same components as those of the hydraulic circuit shown in FIG.

  In this embodiment, a variable capacity type is used for the fan driving hydraulic motor 30 for driving the fan 29. The fan drive hydraulic motor 30 is connected to an electric or electrohydraulic regulator 36 for operating the motor capacity, and the controller 10 is electrically connected to the regulator 36. As shown in FIG. 5, the controller 10 sends a control signal such that the regulator 36 increases the motor capacity of the fan driving hydraulic motor 30 as the traveling speed detected by the vehicle speed sensor 35 increases. It is configured to input to the regulator 36.

According to such a configuration, when the vehicle speed is low, that is, when the traveling load is small and the traveling wind for cooling the oil cooler 8 is small, the motor capacity of the fan driving hydraulic motor 30 is reduced to By increasing the rotational speed, and hence the rotational speed of the fan 29, the cooling effect of the fan 29 can be enhanced to compensate for the shortage of the traveling wind. On the other hand, when the vehicle speed is high, that is, when the traveling wind for cooling the oil cooler 8 is sufficiently received but the driving load for traveling is large, the motor capacity of the fan driving motor 30 is increased to increase the fan 29. By reducing the drive pressure, the power of the prime mover 1 consumed to drive the fan drive hydraulic pump 28 can be saved, and the power required for high-speed travel can be ensured.

  Next, a third embodiment of the present invention will be described with reference to FIG.

  In this embodiment, as shown in FIG. 6A, a variable relief valve (an electromagnetic proportional relief in the illustrated example) is provided between the fan driving hydraulic pump 28 and the tank T in parallel with the fan driving hydraulic motor 30. A valve 38) is provided, and the controller 10 is connected to the solenoid of the electromagnetic proportional relief valve 38. Then, as shown in FIG. 6B, the controller 10 increases the set pressure (relief pressure) of the electromagnetic proportional relief valve 38 as the traveling speed detected by the vehicle speed sensor 35 shown in FIG. The control signal to be lowered is input to the solenoid of the electromagnetic proportional relief valve 38.

  Even in such a configuration, when the vehicle speed is low, that is, when the traveling load is small and the traveling wind for cooling the oil cooler 8 is small, the set pressure of the electromagnetic proportional relief valve 38 is increased to drive the fan. By increasing the driving pressure of the hydraulic motor 30 and increasing the rotational speed of the fan 29, the cooling effect by the fan 29 can be enhanced to compensate for the shortage of the traveling wind. On the other hand, when the vehicle speed is high, that is, when the traveling wind for cooling the oil cooler 8 is sufficiently received but the traveling load is large, the set pressure of the electromagnetic proportional relief valve 38 is lowered to lower the driving pressure of the fan 29, By reducing the power of the prime mover 1 required to drive the drive hydraulic pump 28, the power necessary for high-speed travel can be ensured.

  In addition, even if the fan drive hydraulic pump 28 is constituted by a variable displacement hydraulic pump and the pump capacity of the fan drive hydraulic pump 28 is reduced as the running speed increases, the hydraulic oil cooling during high speed running can be reduced. It is possible to reduce the power required for this.

(A) (b) is a figure which shows the example of the arrangement | positioning location of the oil cooler which concerns on this invention. It is a circuit diagram which shows the hydraulic fluid cooling device of the hydraulic travel circuit which concerns on the 1st Embodiment of this invention. It is a graph which shows the control characteristic of the apparatus shown in FIG. It is a circuit diagram which shows the hydraulic fluid cooling device of the hydraulic travel circuit which concerns on the 2nd Embodiment of this invention. It is a graph which shows the control characteristic of the apparatus shown in FIG. (A) is a circuit diagram which shows the hydraulic-oil cooling device of the hydraulic traveling circuit which concerns on the 3rd Embodiment of this invention, (b) is a graph which shows the control characteristic of the device.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Prime mover 3 Working hydraulic pump 4 Traveling main pump 5 Working pump regulator 6 Working circuit 8 Oil cooler 10 Controller (operation control means)
DESCRIPTION OF SYMBOLS 14 Traveling pump regulator 16 Replenishment hydraulic pump 22 Traveling hydraulic motor 28 Fan driving hydraulic pump 29 Fan 30 Fan driving hydraulic motor 35 Vehicle speed sensor (traveling speed detecting means)
36 Regulator 38 Electromagnetic proportional relief valve (variable relief valve)
40 Lower traveling body 42 Traveling wheel 44 Upper turning body 46 Boom 48 Motor cover 52 Louver

Claims (6)

A hydraulic traveling device that hydraulically travels a work vehicle on which a prime mover and a work machine are mounted,
A working hydraulic pump that is driven by the prime mover to supply the working oil to the working machine, an oil cooler that cools the working oil discharged from the working hydraulic pump before returning to the tank, and the vehicle A hydraulic circuit that includes a traveling hydraulic motor for performing the traveling drive of the vehicle and a traveling hydraulic pump that is driven by the prime mover and supplies hydraulic oil in the tank to the traveling hydraulic motor.
The oil cooler is provided at a position for receiving the traveling wind of the work vehicle, and is configured to cool the hydraulic oil using at least the traveling wind; and
Travel speed detecting means for detecting the travel speed of the vehicle;
An operation control means for controlling the operation of the hydraulic circuit so as to reduce the load on the prime mover for cooling the hydraulic oil by the oil cooler as the traveling speed detected by the traveling speed detection means increases. A hydraulic traveling device for a work vehicle characterized by the above.   2. The hydraulic travel device for a work vehicle according to claim 1, wherein the working hydraulic pump is constituted by a variable displacement hydraulic pump, and the operation control means has a higher travel speed detected by the travel speed detection means. A hydraulic travel device that reduces the pump capacity of the working hydraulic pump.   2. The hydraulic travel device for a work vehicle according to claim 1, further comprising a fan that gives artificial wind to the oil cooler to enhance its cooling performance, and the hydraulic circuit includes a fan driving hydraulic motor for driving the fan; And a fan drive hydraulic pump that is driven by the prime mover and supplies hydraulic oil to the fan drive hydraulic motor, wherein the operation control means increases the travel speed detected by the travel speed detection means. A hydraulic travel device characterized by controlling the operating state of the hydraulic circuit so as to reduce the driving load of the hydraulic pump for driving the fan.   4. The hydraulic travel device for a work vehicle according to claim 3, wherein the fan drive hydraulic motor is constituted by a variable displacement hydraulic motor, and the operation control means has a high travel speed detected by the travel speed detection means. A hydraulic travel device characterized by increasing the motor capacity of the variable displacement hydraulic motor.   4. The hydraulic travel device for a work vehicle according to claim 3, wherein a variable relief valve is provided in parallel with the fan drive hydraulic motor, and the operation control means has a higher travel speed detected by the travel speed detection means. A hydraulic travel device that reduces the relief pressure of the variable relief valve.   The hydraulic traveling device for a work vehicle according to any one of claims 1 to 5, wherein as the traveling hydraulic pump, a traveling main pump constituting a traveling hydraulic circuit including a closed circuit together with the traveling hydraulic motor, A hydraulic traveling device comprising: a traveling hydraulic circuit comprising a closed circuit; and a replenishing hydraulic pump for replenishing hydraulic oil in the tank.

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