Work vehicle

A work vehicle includes an engine, an exhaust gas purification apparatus, a reducing agent tank, an engine coolant circuit, a branch path, a valve, an accepting portion, and a valve control unit. The exhaust gas purification apparatus purifies a nitrogen oxide in an exhaust gas. The reducing agent tank stores a reducing agent to be supplied to the exhaust gas purification apparatus. The engine coolant circuit includes a water pump for circulating a engine coolant through a circulation path as the engine is driven. The branch path is provided for heat exchange between the engine coolant and the reducing agent in the reducing agent tank. The valve controls supply of the engine coolant into the branch path. The accepting portion accepts an operation instruction from an operator. The valve control unit gives an instruction for an opening operation of the valve in response to the operation instruction from the operator.

TECHNICAL FIELD

The present invention relates to a work vehicle.

BACKGROUND ART

An exhaust treatment apparatus is mounted on such a work vehicle as a hydraulic excavator, a bulldozer, and a wheel loader. As the exhaust treatment apparatus, for example, a diesel particulate filter apparatus (DPF), a diesel oxidation catalyst apparatus (DOC), a selective catalytic reduction apparatus (SCR), and the like are available.

An exhaust treatment apparatus reduces a nitrogen oxide (NOx) contained in a gas exhausted from an engine (an exhaust gas), to a harmless gas through NOx reduction reaction. A work vehicle includes a reducing agent tank for storing a reducing agent for NOx reduction reaction, and the reducing agent stored in the reducing agent tank is injected into the exhaust gas.

When an outside temperature is low and when a reducing agent stored in a reducing agent tank is frozen, there is a possibility that the reducing agent cannot be supplied to the exhaust treatment apparatus.

Therefore, for prevention of freeze of a reducing agent stored in a reducing agent tank, PTD 1 proposes a scheme for preventing a reducing agent from freezing, by introducing an engine coolant into a reducing agent tank and exchanging heat between the engine coolant and the reducing agent.

CITATION LIST

Patent Document

SUMMARY OF INVENTION

Technical Problem

Specifically, PTD 1 proposes a scheme for preventing a reducing agent from freezing by exchanging heat between a reducing agent and a coolant which flows through a path formed by branching a part of a circulation path for an engine coolant and introducing the path into a reducing agent tank.

In a case that an engine coolant is introduced into a reducing agent tank as in PTD 1, a new path is added to a path through which the engine coolant circulates. Here, air should sufficiently be released before making use of an additional path. If release of air is insufficient, the coolant is not sufficiently supplied to the path and efficiency in heat exchange is lowered.

The present invention was made to solve the problem described above, and an object of the present invention is to provide a work vehicle in which air in a path for supplying an engine coolant into a reducing agent tank can sufficiently be released.

Other tasks and novel features will become apparent from the description herein and the attached drawings.

Solution to Problem

A work vehicle according to one aspect of the present invention includes an engine, an exhaust gas purification apparatus, a reducing agent tank, an engine coolant circuit, a branch path, a valve, an accepting portion, and a valve control unit. The exhaust gas purification apparatus purifies a nitrogen oxide in an exhaust gas emitted from the engine. The reducing agent tank stores a reducing agent to be supplied to the exhaust gas purification apparatus. The engine coolant circuit includes a water pump for circulating a coolant for cooling of the engine through a circulation path as the engine is driven. The branch path is provided for heat exchange between the engine coolant and the reducing agent in the reducing agent tank. The valve controls supply of the engine coolant into the branch path. The accepting portion accepts an operation instruction from an operator. The valve control unit gives an instruction for an opening operation of the valve in response to the operation instruction from the operator.

According to the work vehicle in the present invention, the valve control unit gives an instruction for an opening operation of the valve in response to an operation instruction from an operator. Thus, since a coolant is supplied from a circulation path to a branch path in response to the operation instruction from the operator, air in the branch path is pushed out to the circulation path and air is sufficiently released.

Preferably, the accepting portion is implemented by a monitor apparatus. The monitor apparatus outputs the operation instruction to the valve control unit.

According to the above, the accepting portion is implemented by a monitor apparatus and the monitor apparatus outputs an operation instruction to the valve control unit. Thus, the operator can easily give an instruction to perform processing for releasing air.

Preferably, the valve control unit is configured to give an instruction for a closing operation of the valve after lapse of a prescribed period since it gave the instruction for the opening operation of the valve.

According to the above, since an instruction for a closing operation of the valve is given after lapse of a prescribed period, it is not necessary to request an operation from an operator and convenience can be enhanced.

Preferably, the reducing agent tank is provided on one end side in a longitudinal direction of a body frame, and the engine is provided on the other end side of the body frame.

According to the above, since the reducing agent tank and the engine are provided on one end side and the other end side in a longitudinal direction of the body frame, respectively, influence by the engine which is a heat source on the reducing agent tank can be suppressed.

Preferably, the branch path has a low region provided in midstream of a path through which the engine coolant flows and a high region higher than the low region provided downstream of the low region.

According to the above, the branch path can allow sufficient air release also in a construction in which it is difficult to release air represented by a case of a region having a height difference from low to high in midstream of a path.

A method of controlling a work vehicle according to one aspect of the present invention includes the steps of outputting a command signal for increasing the number of rotations of an engine, accepting an instruction for an opening operation by an operator, of a valve provided in a path for introducing an engine coolant into a reducing agent tank, and outputting an instruction signal indicating an opening operation of the valve in response to acceptance of the instruction for the opening operation by the operator after increase in number of rotations of the engine.

According to the method of controlling a work vehicle in the present invention, the step of outputting an instruction signal indicating an opening operation of a valve in response to acceptance of the instruction for the opening operation by an operator after increase in number of rotations of an engine is included. Thus, since an operation for opening the valve is performed with the number of rotations of the engine having been increased, a coolant is supplied into a path for supplying the coolant into a reducing agent tank, and air is sufficiently released.

Advantageous Effects of Invention

Air in a path for supplying an engine coolant into a reducing agent tank can sufficiently be released.

DESCRIPTION OF EMBODIMENTS

FIG. 1is a diagram illustrating appearance of a work vehicle101based on an embodiment.

As shown inFIG. 1, in the present example, a hydraulic excavator will mainly be described by way of example as work vehicle101based on the embodiment.

Work vehicle101mainly includes a lower carrier1, an upper revolving unit3, and a work implement4. A work vehicle main body is constituted of lower carrier1and upper revolving unit3. Lower carrier1has a pair of left and right crawler belts. Upper revolving unit3is attached revolvably, with a revolving mechanism in an upper portion of lower carrier1being interposed.

Work implement4is pivotably supported by upper revolving unit3in a manner operable in a vertical direction and performs such working as excavation of soil. Work implement4includes a boom5, an arm6, and a bucket7. Boom5has a root portion movably coupled to upper revolving unit3. Arm6is movably coupled to a tip end of boom5. Bucket7is movably coupled to a tip end of arm6. In addition, upper revolving unit3includes an operator's cab8or the like.

FIG. 2is a perspective view showing an internal construction of operator's cab8based on the embodiment.

As shown inFIG. 2, operator's cab8has an operator's seat9, a travel operation portion10, a pedal for attachment15, a side window16, a dashboard17, work implement levers18,1.9, a locking lever20, a monitor apparatus21, a front window22, and a vertical frame23.

Operator's seat9is provided in a central portion of operator's cab8. Travel operation portion10is provided in front of operator's seat9.

Travel operation portion10includes travel levers11,12and travel pedals13,14. Travel pedals13,14can move together with respective travel levers11,12. Lower carrier1moves forward as an operator pushes forward travel lever11,12. Alternatively, lower carrier1moves backward as the operator pulls backward travel lever11,12.

Pedal for attachment15is provided in the vicinity of travel operation portion10. In addition, dashboard17is provided in the vicinity of right side window16inFIG. 2.

Work implement levers18,19are provided in left and right portions of operator's seat9, respectively. Work implement lever18,19serves to carry out vertical movement of boom5, pivot of arm6and bucket7, a revolving operation of upper revolving unit3, and the like.

Locking lever20is provided in the vicinity of work implement lever18. Here, locking lever20serves to stop such functions as operation of work implement4, revolution of upper revolving unit3, and travel of lower carrier1. By performing an operation for positioning locking lever20in a vertical state (here, an operation for pulling down the locking lever), movement of work implement4or the like can be locked (restricted).

Monitor apparatus21is provided in a lower portion of vertical frame23which is a partition between front window22and one side window16of operator's cab8and it displays an engine state of work vehicle101, guidance information, warning information, or the like. In addition, monitor apparatus21is provided to be able to accept a setting instruction as to various operations of work vehicle101.

Here, an engine state refers, for example, to a temperature of an engine coolant, a temperature of hydraulic oil, an amount of remaining fuel, and the like. Guidance information includes an indication and the like inviting check and maintenance of the engine of the work vehicle, by way of example. Various operations refer, for example, to setting of a prescribed mode (an air release mode). Warning information is information to which operator's attention should be called.

<Configuration of Control System>

FIG. 3is a simplified diagram showing a configuration of a control system of work vehicle101based on the embodiment.

As shown inFIG. 3, the control system of work vehicle101includes, by way of example, work implement lever18,19and travel lever11,12, locking lever20, monitor apparatus21, a first hydraulic pump31A, a second hydraulic pump31B, a swash plate drive apparatus32, a control valve34, a hydraulic actuator35, an engine36, and an engine controller38. The control system further includes a fuel dial39, a rotation sensor40, a work implement lever apparatus41, a pressure switch42, a valve43, a potentiometer45, a starter switch46, a pressure sensor47, a main controller50, a radiator71, a thermostat76, a water pump61, a circulation path74, a branch path70, a sensor73, and a long life coolant (LLC) valve75.

In addition, the control system of work vehicle101further includes an exhaust gas purification apparatus60and a reducing agent tank69.

Exhaust gas purification apparatus60further includes an exhaust purification unit62, a relay connection pipe (mixing piping)64, a selective catalytic reduction apparatus65, a flue66, and a reducing agent injector84.

Reducing agent injector84has a reducing agent supply path83and a reducing agent injection valve68.

Exhaust purification unit62includes a diesel oxidation catalyst apparatus62A and a diesel particulate filter apparatus62B.

First hydraulic pump31A discharges hydraulic oil used for driving work implement4or the like.

Second hydraulic pump31B discharges oil made use of for generating a hydraulic pressure (a pilot pressure) in accordance with an operation of work implement lever18,19and travel lever11,12. Swash plate drive apparatus32is connected to first hydraulic pump31A.

Swash plate drive apparatus32drives based on an instruction from main controller50and changes an angle of inclination of a swash plate of first hydraulic pump31A. Hydraulic actuator35is connected to first hydraulic pump31A with control valve34being interposed. Hydraulic actuator35is a cylinder for boom, a cylinder for arm, a cylinder for bucket, a hydraulic motor for revolution, a hydraulic motor for travel, and the like.

Control valve34is connected to work implement lever apparatus41. Work implement lever apparatus41outputs to control valve34, a pilot pressure in accordance with a direction of operation and/or an amount of operation of work implement lever18,19and travel lever11,12. Control valve34controls hydraulic actuator35in accordance with the pilot pressure.

Work implement lever18,19and travel lever11,12as well as locking lever20are connected to second hydraulic pump31B.

Pressure sensor47is connected to work implement lever apparatus41. Pressure sensor47outputs to main controller50, a lever operation signal in accordance with a state of operation of work implement lever18,19and travel lever11,12.

In response to an instruction from main controller50as will be described later, main controller50carries out such control that first hydraulic pump31A absorbs best matching torque at each output point of engine36, in accordance with pump absorption torque set in accordance with an amount of working, the number of rotations of the engine set with fuel dial39or the like, the actual number of rotations of the engine, and the like.

Engine36has a drive shaft connected to first hydraulic pump31A and second hydraulic pump31B.

Engine controller38controls an operation of engine36in accordance with an instruction from main controller50. Engine36is a diesel engine by way of example. The number of engine rotations of engine36is set with fuel dial39or the like and the actual number of engine rotations is detected by rotation sensor40. Rotation sensor40is connected to main controller50.

Fuel dial39is provided with potentiometer45, which detects an amount of operation of fuel dial39and outputs a value indicated by a dial (also referred to as a dial indication value) regarding the number of rotations of engine36to engine controller38. A target number of rotations of engine36is adjusted in accordance with the dial indication value of fuel dial39.

In response to an instruction from main controller50, engine controller38controls an amount of injection of fuel injected by a fuel injector and adjusts the number of rotations of engine36, based on the dial indication value. Engine controller38adjusts the number of engine rotations of engine36in accordance with a control instruction from main controller50to first hydraulic pump31A.

Starter switch46is connected to engine controller38. As the operator operates starter switch46(sets the starter switch to start), a start signal is output to engine controller38so that engine36starts.

Main controller50is a controller controlling overall work vehicle101, and it is configured with a CPU (Central Processing Unit), a non-volatile memory, a timer, and the like. Main controller50controls engine controller38and monitor apparatus21. Though main controller50and engine controller38are separate from each other in the present example, one common controller can also be provided.

Pressure switch42is connected to locking lever20. Pressure switch42senses an operation of locking lever20when it is operated toward a locking side, and sends a signal to valve (solenoid valve)43. Since valve43thus cuts off supply of oil, such functions as operation of work implement4, revolution of upper revolving unit3, and travel of lower carrier1can be stopped. In addition, pressure switch42sends a similar signal also to main controller50.

Water pump61circulates an engine coolant in circulation path74as engine36is driven. Circulation path74is coupled to radiator71for cooling the engine coolant, with thermostat76being interposed. Thermostat76opens when the engine coolant attains to a prescribed temperature and closes when the engine coolant is lower than a prescribed temperature. Thus, when the engine coolant attains to a prescribed temperature, the engine coolant flows into radiator71, and when the engine coolant is lower than a prescribed temperature, no engine coolant flows into radiator71.

Branch path70is provided in circulation path74. In the present example, branch path70starts from a branch point A, is introduced into reducing agent tank69, and ends at a branch point B.

Branch path70is introduced into reducing agent tank69. In reducing agent tank69, heat is exchanged between the engine coolant which flows through the branch path and the reducing agent stored in reducing agent tank69.

LLC valve75is provided around branch point A in branch path70. LLC valve75performs an opening and closing operation in response to an instruction from main controller50. In response to an instruction to perform an opening operation from main controller50, LLC valve75is opened. Thus, the engine coolant is supplied from branch point A of circulation path74through branch path70into reducing agent tank69, and the engine coolant returns to branch point B of circulation path74.

Sensor73is provided in circulation path74, and detects a state of the engine coolant in the path. In the present example, a temperature of the engine coolant is detected as a state of the engine coolant. Sensor73outputs a detection result obtained from circulation path74to main controller50.

Radiator71is provided with a replenishment port for replenishment with the engine coolant. The replenishment port also functions as an air release port for air which stays in a path through which the engine coolant circulates.

Diesel oxidation catalyst apparatus62A has a function to decrease nitric oxide (NO) of nitrogen oxides (NOx) in the exhaust gas from engine36and increase nitrogen dioxide (NO2).

Diesel particulate filter apparatus62B is an apparatus treating an exhaust from engine36. Diesel particulate filter apparatus62B is constructed to collect particulate matters included in the exhaust from engine36with a filter and burn the collected particulate matters. The filter is composed, for example, of ceramics.

Selective catalytic reduction apparatus65serves to reduce a nitrogen oxide NOx by using ammonia (NH3) resulting from hydrolysis, for example, of a urea solution as a reducing agent. Selective catalytic reduction apparatus65applies, in principle, chemical reaction of a nitrogen oxide (NOx) with ammonia (NH3), which results in reduction to nitrogen (N2) and water (H2O). For example, reducing agent tank69containing a urea solution is mounted on work vehicle101. It is noted that the reducing agent is not limited to a urea solution and a reducing agent should only be able to reduce a nitrogen oxide NOx.

Relay connection pipe (mixing piping)64connects between diesel particulate filter apparatus62B and selective catalytic reduction apparatus65. In this mixing piping64, a reducing agent is injected to an exhaust gas from the diesel particulate filter apparatus to selective catalytic reduction apparatus65and mixed.

Reducing agent injector84injects a reducing agent (a urea solution) pumped up from reducing agent tank69into the exhaust gas through reducing agent supply path83and reducing agent injection valve68.

A sensor72is provided for reducing agent tank69and detects a state of a reducing agent stored in reducing agent tank69. In the present example, a temperature of the reducing agent is detected as a state of the reducing agent. Then, sensor72outputs a result of detection from reducing agent tank69to main controller50.

Flue66is connected to selective catalytic reduction apparatus65and it serves to exhaust an exhaust which has passed through selective catalytic reduction apparatus65into the atmosphere.

It is noted that engine36, exhaust gas purification apparatus60, reducing agent tank69, water pump61and circulation path74, branch path70, LLC valve75, and main controller50represent examples of the “engine”, the “exhaust gas purification apparatus,” the “reducing agent tank,” the “engine coolant circuit,” the “branch path”, the “valve”, and the “valve control unit” of the present invention, respectively.

<Construction of Branch Path>

FIG. 4is a diagram illustrating a path connected to reducing agent tank69based on the present embodiment.

Referring toFIG. 4, initially, an exhaust treatment unit is described. Engine36and the exhaust treatment unit are supported by a body frame95independently of each other.

Specifically, as features of a support for supporting the exhaust treatment unit on the frame, two plates91, four vertical frames (pillar members)92, a horizontal frame93, and a bracket94are provided.

Each of two plates91has a flat plate shape and is attached to body frame95. Each of four vertical frames92has a shape like a pillar and is attached to plate91. Each of four vertical frames92extends upward from a position of attachment to plate91.

Horizontal frame93is attached to vertical frame92. Horizontal frame93is a portion for supporting exhaust purification unit62and selective catalytic reduction apparatus65.

Bracket94has a flat plate shape. It is attached to horizontal frame91A construction in which urea solution piping (reducing agent supply path) connects relay connection pipe (mixing piping)64and reducing agent tank69to each other is shown.

Selective catalytic reduction apparatus65serves to selectively reduce a nitrogen oxide NOx, for example, by making use of ammonia obtained by hydrolysis of a urea solution. Therefore, an apparatus supplying a urea solution to selective catalytic reduction apparatus65is required.

This reducing agent injector84mainly has reducing agent injection valve68and reducing agent supply path83.

Reducing agent tank69is constructed to be able to store the urea solution. This reducing agent tank69is arranged, for example, outside an engine room, and supported by body frame95.

Reducing agent supply path83connects this reducing agent tank69and mixing piping64to each other. This reducing agent supply path83can guide the urea solution stored in reducing agent tank69to mixing piping64.

The urea solution stored in reducing agent tank69is injected and supplied into mixing piping64from reducing agent injection valve68through reducing agent supply path83.

In reducing agent injector84above, reducing agent supply path83is connected as extending from the same side in a longitudinal direction (an X direction) (a front side in the drawing) as a portion of connection of mixing piping64to exhaust purification unit62. A connection portion of reducing agent supply path83to mixing piping64is on the upstream side of an exhaust path in mixing piping64. Thus, the urea solution injected and supplied to mixing piping64is evenly mixed with the exhaust while it runs from upstream to downstream in mixing piping64.

Water pump61is provided adjacent to engine36and water pump61is connected to circulation path74. Branch point A and branch point B of circulation path74and branch path70are connected to each other. Branch path70is provided in a detachable and attachable manner, with respect to branch points A and B of circulation path74.

Vertical frames96A and96B to which work implement4is attached are provided in body frame95, and reducing agent supply path83is arranged to extend along vertical frame96A (in the X direction).

Similarly to reducing agent supply path83, branch path70is also arranged to extend along vertical frame96A (in the X direction).

Reducing agent supply path83and branch path70with respect to reducing agent tank69are both arranged to extend along a direction from a lower surface portion of reducing agent tank69to an upper surface portion (in a Z direction) around reducing agent tank69.

In the present example, reducing agent tank69is arranged at a front end portion (on a front side in the figure) in the longitudinal direction (in the X direction) of body frame95, while engine36is arranged at a rear end portion (on a rear side in the figure) in the longitudinal direction (in the X direction) of body frame95. By thus arranging reducing agent tank69away from engine36, deterioration of quality of the reducing agent in reducing agent tank69due to influence by a heat source such as engine36can be suppressed. By spacing reducing agent tank69apart from engine36, a path length of branch path70increases.

FIG. 5is a diagram illustrating an internal state of reducing agent tank69based on the present embodiment.

Referring toFIG. 5, branch path70is introduced into reducing agent tank69. Branch path70is arranged along a direction from the lower surface portion of reducing agent tank69to the upper surface portion around reducing agent tank69, is introduced from the upper surface side of reducing agent tank69, reaches a bottom portion in reducing agent tank69, and thereafter is turned around, and is again taken out of the upper surface side of reducing agent tank69.

Therefore, branch path70has a region provided with a height difference from low to high in midstream of the path. Branch path70has a low region provided in midstream of the path through which the engine coolant flows and a high region provided downstream of the low region.

For example, branch path70has such a construction that a low region which is the lower surface portion around reducing agent tank69, a high region which is the upper surface side of reducing agent tank69, and a low region which is the bottom portion in reducing agent tank69are continuous. The high region of branch path70is provided between the low region before reducing agent tank69and the low region within reducing agent tank69.

Therefore, at least a height difference from low to high by a height of reducing agent tank69is provided in midstream of branch path70.

A configuration of monitor apparatus21will now be described.

FIG. 6is a diagram illustrating a configuration of monitor apparatus21based on the embodiment.

As shown inFIG. 6, monitor apparatus21includes an input portion211, a display portion212, and a display control unit213.

Input portion211accepts input of various types of information. Monitor apparatus21is connected to main controller50, and input accepted at input portion211is output to main controller50.

Display portion212is implemented by a liquid crystal screen or the like.

Display control unit213controls display contents on display portion212. Specifically, display control unit213provides display of information on an operation of work vehicle101in response to an instruction from main controller50. The information includes information on an engine state or guidance information, warning information, and the like.

Input portion211will specifically be described. Input portion211is constituted of a plurality of switches. Input portion211has function switches F1to F6.

Function switches F1to F6are located in a lower portion of display portion212and displayed as “F1” to “F6”, respectively. They are switches each for inputting a signal corresponding to an icon displayed on display portion212above each switch (by way of example, guidance icons I1to I3).

In addition, input portion211has a deceleration switch111, an operation mode selection switch112, a travel speed gear selection switch113, a buzzer cancellation switch114, a wiper switch115, a washer switch116, and an air-conditioner switch117, provided under function switches F1to F6.

Deceleration switch111is a switch for carrying out deceleration control for lowering the number of engine rotations of engine36to a prescribed number of rotations a prescribed time period after work implement lever18,19returned to a neutral position. The “neutral position” refers to a state that work implement lever18,19is not operated (a non-working state).

Operation mode selection switch112is a switch for selecting an operation mode of work vehicle101from among a plurality of operation modes. Travel speed gear selection switch113is a switch for selecting a travel speed gear of work vehicle101from among a plurality of travel speed gears. Buzzer cancellation switch114is a switch for cancelling buzzer sound generated at the time when work vehicle101is in a prescribed warning condition. Wiper switch115is a switch for operating a wiper (not shown) provided in a windshield of operator's cab8(seeFIG. 2) of work vehicle101. Washer switch116is a switch for actuating a washer (not shown) for injecting cleaning water toward the windshield. Air-conditioner switch117is a switch for operating various functions of an air-conditioner within operator's cab8.

It is noted that a touch panel of a resistive film type or the like is also applicable as input portion211. In the present example, a case where work vehicle101displays a standard picture301displayed during a normal operation as a picture displayed on display portion212is shown.

Standard picture301is generated by display control unit213based on picture data stored in advance in a not-shown memory. This is also the case with other pictures.

In standard picture301, an engine water temperature gauge G1, a hydraulic oil temperature gauge G2, and a fuel level gauge G3are displayed as aligned, and a pointer of a gauge changes based on a sensor signal from each corresponding sensor. In addition, a fuel consumption gauge G4is displayed on the right of fuel level gauge G3.

A clock W is displayed in an upper central portion of display portion212. On the right of clock W, an operation mode icon IU indicating a set operation mode and a travel speed gear icon IS indicating a set travel speed gear are displayed.

In standard picture301, a character “P” is displayed as operation mode icon IU. This is an indication of a case where an operation mode is set to a power mode made use of in normal excavation working or the like.

In contrast, in a case where work vehicle101is set to an economy mode, it is assumed that a character “E” is displayed as operation mode icon IU.

At a position in a lower portion of standard picture301and above function switches F4to F6, guidance icons I1to I3corresponding to function switches F4to F6, respectively, are displayed.

Guidance icon I1is an icon meaning switching of a picture displayed on display portion212to a camera screen. The camera screen is a screen output by means of an image signal obtained by a CCD camera or the like (not shown) installed on the exterior of work vehicle101and shooting an outside world of work vehicle101. Guidance icon12is an icon meaning switching of display of clock W to display of a service meter. Guidance icon I3is an icon meaning switching of a picture displayed on display portion212to a user mode picture. Therefore, for example, when function switch F4corresponding to guidance icon I1is pressed, a picture displayed on display portion212is switched to a camera screen.

FIG. 7is a diagram illustrating one example of an air release mode selection picture based on the embodiment.

As shown inFIG. 7, an air release mode selection picture302is displayed as transition from standard picture301as a result of selection of a prescribed function switch by way of example. Air release mode selection picture302is operated before branch path70is made use of.

In the present example, in air release mode selection picture302, a picture capable of accepting an input instruction for setting an opened state or a closed state of the LLC valve is shown.

In the present example, in connection with opening and closing of the LLC valve, an “open” item303and a “close” item304are provided.

When an operator selects “open” item303and indicates execution, LLC valve75is set to the opened state. By moving a cursor over a position of “close” item304and indicating execution, LLC valve75can also be set to the closed state. Thus, monitor apparatus21serves as an accepting portion for accepting an operation instruction from an operator.

After lapse of a prescribed period sufficient for determining that air release ended after opening of LLC valve75, LLC valve75may automatically be set to the closed state. With such processing, convenience for an operator can be enhanced.

In the present embodiment, branch path70is provided for heat exchange with the reducing agent in reducing agent tank69.

In the present embodiment, before making use of branch path70, “open” item303is selected in air release mode selection picture302, so that LLC valve75is opened and the engine coolant is supplied to branch path70. Thus, air in branch path70is pushed out to circulation path74. Then, in radiator71coupled to circulation path74, air in the path is emitted into the outside air.

Therefore, air in branch path70for supplying the engine coolant into reducing agent tank69can sufficiently be released before branch path70is made use of Thus, lowering in efficiency in heat exchange can be suppressed.

Though monitor apparatus21accepts an instruction for opening and closing of the LLC valve in the present example, limitation to monitor apparatus21is not particularly intended, and such a member as a button for accepting an instruction for opening and closing of the LLC valve may be provided independently of monitor apparatus21and used to accept an instruction for opening and closing of the LLC valve.

A scheme with which air in a path for supplying the engine coolant into the reducing agent can more effectively be released will be described.

FIG. 8is a diagram illustrating the number of rotations of the engine and a temperature of an engine coolant, as well as timing to start the air release mode based on the present embodiment.

As shown inFIG. 8, here, the left ordinate represents the number of rotations of the engine and the abscissa represents time t. The right ordinate represents a temperature of the engine coolant. Here, a line L1indicates the number of rotations of the engine and a line L2indicates a temperature of a coolant.

After engine36is started, the number of engine rotations of engine36is set to the number of engine rotations F1representing a low idling state. A temperature of the engine coolant increases with start of engine36. A temperature of the engine coolant is detected by sensor73. A case that a temperature of the engine coolant attained to X° C. at time T1is shown.

When the temperature of the engine coolant attains to X° C. at time T1, the number of engine rotations is set to the number of engine rotations F2representing a high idling state. This is because, if the number of engine rotations is increased while a temperature of the engine coolant is low, load imposed on engine36becomes high. Though a temperature of the engine coolant is lower than X° C. in an initial state in the present example, when a temperature is X° C. in the initial state, the number of engine rotations may initially be set to the number of engine rotations F2representing the high idling state.

After the number of engine rotations is set to the high idling state, the air release mode is set to on (open).

In the present embodiment, the air release mode is set to on (open) so as to release air in circulation path74while the number of engine rotations F2is in the high idling state. Water pump61in the present embodiment supplies the engine coolant to circulation path74with driving force from engine36. Therefore, with increase in number of rotations of engine36, a pressure of supply of the engine coolant from water pump61to circulation path74is higher. Accordingly, when LLC valve75of circulation path74is opened in the high idling state at the number of engine rotations F2, the engine coolant is supplied with a supply pressure to branch path70being high. Therefore, air in branch path70is released by the engine coolant high in supply pressure, so that air in branch path70is pushed out to circulation path74and air can effectively be released.

FIG. 9is a flowchart illustrating processing in the air release mode in main controller50of work vehicle101based on the embodiment.

As shown inFIG. 9, initially, whether or not the engine has started is determined (step S1). Main controller50determines whether or not engine controller38has caused engine36to start.

Then, a temperature of the engine coolant is detected (step S2). Main controller50detects a temperature of the engine coolant from sensor73.

Then, whether or not a temperature of the engine coolant is lower than Q° C. is determined (step S3). Main controller50determines whether or not a temperature of the engine coolant is lower than Q° C. based on a result of detection obtained from sensor73.

When it is determined in step S3that a temperature of the engine coolant is lower than Q° C. (YES in step S3), that state is maintained. When it is determined in step S3that a temperature of the engine coolant is not lower than Q° C. (NO in step S3), the high number of rotations is set (step S4). When main controller50determines that a temperature of the engine coolant is not lower than Q° C., it instructs engine controller38to set the number of engine rotations to the high number of rotations.

Then, the air release mode is activated (step S5). Main controller50makes setting so as to allow acceptance of an instruction for opening and closing of the LLC valve in air release mode selection picture302. For example, selection of a prescribed function switch described with reference toFIG. 6may be activated.

Though the air release mode is activated after the number of engine rotations is set to the high number of rotations in the present example, limitation to that scheme is not intended. An instruction for the air release mode can be accepted even before the number of engine rotations is set to the high number of rotations, and an instruction for the air release mode may be executed after the number of engine rotations is set to the high number of rotations.

Then, whether or not an instruction for opening has been given is determined (step S6). Main controller50determines whether or not “open” item303has been selected in air release mode selection picture302.

After stand-by until an instruction for opening is given and when it is determined in step S6that an instruction for opening has been given (YES in step S6), LLC valve75is set to the opened state. When “open” item303has been selected, main controller50instructs LLC valve75to be in the opened state.

Then, whether or not a prescribed period has elapsed is determined (step S8). Main controller50determines whether or not a prescribed period has elapsed after LLC valve75is set to the opened state.

The prescribed period is desirably set to a period equal to or longer than a time period from a time point of start of engine36until thermostat76opens as a result of increase in temperature of the engine coolant.

Thus, by making determination with a time period from a time point of start of engine36until opening of thermostat76being defined as the reference, air in the entire path for the engine coolant (circulation path74+branch path70) can be released.

For example, approximately 15 minutes can be set as a prescribed period. The period is by way of example, and any length may be set so long as air release processing can be performed.

When it is determined in step S8that a prescribed period has elapsed (YES in step S8), LLC valve75is set to the closed state (step S9). Main controller50instructs LLC valve75to be in the closed state when a prescribed period has elapsed after LLC valve75is set to the opened state.

Then, the process ends (end).

With such processing, LLC valve75can be set to the opened state and air in branch path70can be released while the engine is set to the high number of rotations.

For example, in a case that a path length of branch path70is long or a height difference (for example, a height difference by a height of reducing agent tank69) is provided in midstream of branch path70, a pressure for pushing air in branch path70from branch path70into circulation path74is necessary. Though air cannot sufficiently be released in a case that a pumping pressure of water pump61is low, with the scheme in the present embodiment, a pumping pressure of water pump61can be increased so that the engine coolant can be supplied to branch path70. Thus, air can sufficiently be released.

Though a hydraulic excavator has been described by way of example of a work vehicle, application also to such a work vehicle as a bulldozer or a wheel loader is possible, and application to any work machine provided with engine36is possible.

Though the embodiment of the present invention has been described above, it should be understood that the embodiment disclosed herein is illustrative and non-restrictive in every respect. The scope of the present invention is defined by the terms of the claims, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

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