Work machine

A work machine provided with an exhaust gas purifying device includes a selective catalytic reducing device that performs treatment on exhaust gas of an engine, and a reducing agent injection device that injects a reducing agent into exhaust gas to be supplied to the selective catalytic reducing device. The work machine is provided with a housing that delimits an engine room accommodating the engine and the exhaust gas purifying device. The housing includes a top board that covers the engine room above the engine, and an exhaust duct that is provided in the top board and discharges the air in the engine room to the outside of the engine room. A part of a reducing agent supply pipe for guiding the reducing agent to the reducing agent injection device is disposed in the exhaust duct in a position above the reducing agent injection device.

TECHNICAL FIELD

The present invention relates to a work machine.

BACKGROUND ART

There is known a work machine including an exhaust gas purifying device that removes a nitrogen oxide (NOx) being discharged (cf. Patent Literature 1). Patent Literature 1 describes an exhaust gas after-treatment unit including: a selective catalytic reducing device; a reducing agent injection device that injects a reducing agent, such as a urea aqueous solution, into exhaust gas to be supplied to the selective catalytic reducing device; a cooling water supply pipe that guides cooling water to the injection device; and a cooling water return pipe for discharging the cooling water from the injection device.

The cooling water supply pipe and the cooling water return pipe each include a convection portion extending upward from a portion connected with the injection device along a connection pipe that guides the exhaust gas from the engine to the selective catalytic reducing device. In the technique described in Patent Literature 1, the convection portion is provided in each of the cooling water supply pipe and the cooling water return pipe, and after stopping of the engine, cooling water having increased in temperature due to absorption of heat from the injection device is convected in the convection portion to enable cooling of the injection device.

CITATION LIST

Patent Literature

SUMMARY OF INVENTION

Technical Problem

A reducing agent supply pipe for guiding the reducing agent to the reducing agent injection device is connected to the exhaust gas purifying device. When the temperature of the reducing agent in the reducing agent supply pipe increases due to an influence of heat from a heating element such as the engine, the quality of the reducing agent may deteriorate.

Solution to Problem

A work machine according to one aspect of the present invention is a work machine provided with an exhaust gas purifying device including a selective catalytic reducing device that performs treatment on exhaust gas of an engine, and a reducing agent injection device that injects a reducing agent into exhaust gas to be supplied to the selective catalytic reducing device. The work machine is provided with a housing that delimits an engine room accommodating the engine and the exhaust gas purifying device. The housing includes a top board that covers the engine room above the engine, and an exhaust duct that is provided in the top board and discharges the air in the engine room to the outside of the engine room. A part of a reducing agent supply pipe for guiding the reducing agent to the reducing agent injection device is disposed in the exhaust duct in a position above the reducing agent injection device.

Advantageous Effect of Invention

According to the present invention, it is possible to prevent an increase in temperature of a reducing agent in a reducing agent supply pipe.

DESCRIPTION OF EMBODIMENT

In the following, one embodiment of a work machine (work vehicle) according to the present invention will be described with reference to the drawings. For convenience of description, in the present embodiment, front-rear directions, right-left directions, and up-down directions are defined as put down in each of the drawings. Further in the present embodiment, of members constituting the work machine, description of some or all of members which need to be omitted for description are omitted in each of the drawings.

FIG. 1is a side view of a wheel loader which is one example of a work machine according to one embodiment of the present invention. As shown inFIG. 1, the wheel loader is made up of a front vehicle body110including an arm111, a bucket112, front wheels113, and the like, and a rear vehicle body120including an operator's cab121, a housing122, rear wheels123, and the like.

The arm111vertically rotates (moves up and down) by drive of an arm cylinder (not shown), and the bucket112vertically rotates (crowds and dumps) by drive of the bucket cylinder115. The front vehicle body110and the rear vehicle body120are rotatably coupled to each other with a center pin101, and the front vehicle body110horizontally bent with respect to the rear vehicle body120by shrinkage of the steering cylinder116.

The housing122constitutes an outline of a storage chamber accommodating an engine301, an exhaust gas purifying device400, a heat exchanger, a variety of hydraulic equipment, and the like. Openings on the right and left side surfaces of the housing122are covered by a pair of right and left operable/closable housing covers130. The housing cover130is an opening/closing cover of a gull wing type, and configured to be opened substantially horizontally to the ground, with a rotation fulcrum (hinge) provided between the top board of the housing122and the housing cover130. The housing covers130respectively provided on the right and left side surfaces of the wheel loader100have substantially a bilaterally symmetrical shape.

FIG. 2is a plan view of the wheel loader in a state where the upper structure such as the top board has been removed. As shown inFIG. 2, the storage chamber (storage space) provided inside the housing122is divided by a partition160into an engine room122E on the front side of the vehicle and a cooler chamber122C on the rear side of the vehicle.

As shown inFIG. 1, the side surface of the engine room122E is covered by a part of the housing cover130, and the upper surface of the engine room122E is covered by an engine hood140constituting the top board of the housing122. The front surface of the engine room122E is covered by a front plate811of a front-side frame810(cf.FIG. 4), and the rear surface of the engine room122E is covered by the partition160of a rear-side frame161(cf.FIG. 3). That is, the engine room122E is delimited by the part of the pair of right and left housing covers130, the engine hood140, the front plate811(cf.FIG. 4), and the partition160(cf.FIG. 3).

The side surface of the cooler chamber122C is covered by a part of the housing cover130, and the upper surface of the cooler chamber122C is covered by a housing cover132for cooler which constitutes the top board of the housing122. The front surface of the cooler chamber122C is covered by the partition160, and the rear surface of the cooler chamber122C is covered by a grille200. That is, the cooler chamber122C is delimited by the part of the pair of right and left housing cover130, the housing cover132for cooler, the partition160, and the grille200.

A heat exchanger501and a cooling fan unit502are disposed inside the cooler chamber122C. The heat exchanger501includes: a plurality of heat exchangers such as a radiator504(cf.FIG. 9) that cools the cooling water of the engine301, an oil cooler that cools a hydraulic oil, and an inter cooler that cools the air pressurized by a supercharger of the engine301; and a radiator frame for supporting these heat exchangers. The cooling fan unit502includes a cooling fan503(cf.FIG. 9) for generating cooling wind for cooling the heat exchanger501and a shroud for supporting the cooling fan503(cf.FIG. 9). In accordance with the model of the wheel loader, heat exchangers, such as a transmission oil cooler and a capacitor of an air conditioner for air conditioning in the operator's cab121, are also fitted in the heat exchanger501.

As shown inFIG. 1, an intake pipe145protrudes from the upper surface of the housing cover132for cooler, the intake pipe145being configured to take air necessary for the drive of the engine301via an air cleaner310(cf.FIG. 3). As shown inFIG. 3, the air cleaner310is provided immediately behind the partition160in the cooler chamber122C. The air cleaner310is connected to the engine301via the suction pipe. Providing the air cleaner310in the cooler chamber122C can reduce an influence of heat from the engine301or the exhaust gas purifying device400to the air cleaner310. It is thereby possible to prevent an increase in temperature of air to be sucked by the engine301and prevent deterioration in suction efficiency of the engine301.

As shown inFIG. 1, the exhaust gas purifying device400for purifying the exhaust gas of the engine301is set up above the engine301in the engine room122E. A tale pipe171for discharging the exhaust gas protrudes from the engine hood140.

FIG. 3is a perspective view showing the inside of the cooler chamber122C, andFIG. 4is a perspective view showing the inside of the engine room122E. InFIGS. 3 and 4, the housing cover130, the engine hood140, the housing cover132for cooler, the grille200, and the like which constitute the housing122are omitted.

As shown inFIG. 4, the engine301is fitted in a mounting bracket, not shown, in the rear vehicle body120in the engine room122E. The supercharger (turbocharger)302is fitted in the engine301. The supercharger302is set up such that a suction port of a compressor302ais directed rearward and an exhaust port of a turbine302bis directed forward.

As shown inFIGS. 2 and 4, the exhaust gas purifying device400includes an oxidation catalyst device (DOC: Diesel Oxidation Catalyst)410, a reducing agent injection device (DRT: Decomposition Reactor Tube)420, and a selective catalytic reducing device (SCR: Selective Catalytic Reduction)430, which are installed in an exhaust passage of the engine301. The oxidation catalyst device410, the reducing agent injection device420, and the selective catalytic reducing device430are disposed in this order from the upstream along the flow of the exhaust gas. Each of the after-treatment devices (410,420,430) is connected by a connection pipe such as an elbow.

The oxidation catalyst device410includes: an oxidation catalyst for oxidizing and removes nitric monoxide (NO), carbon monoxide (CO), hydrocarbon (HC), and the like contained in the exhaust gas; and a cylindrical DOC casing411for holding the oxidation catalyst. The reducing agent injection device420is installed downstream of the oxidation catalyst device410.

The reducing agent injection device420includes an injection valve429for injection a urea aqueous solution (hereinafter referred to as urea water) being a reducing agent into the exhaust gas to be supplied to the selective catalytic reducing device430, and a cylindrical DRT housing421for holding the injection valve429. The injection valve429is provided substantially at the center of the DRT housing421. The injection valve429injects urea water into the DRT housing421in accordance with a control signal from a control device, not shown. The injection valve429is opened or closed by allowing a current to flow in a coil to generate a magnetic field in a magnetic circuit including a mover and a core and cause action of magnetic suction force that attracts the mover to the core, and the injection valve429has a similar configuration to that of a known electromagnetic driving fuel injection valve (injector). The selective catalytic reducing device430is installed downstream of the reducing agent injection device420.

The selective catalytic reducing device430includes a reduction catalyst for performing reduction purification treatment on a nitrogen oxide (NOx) contained in the exhaust gas by using urea water as the reducing agent, and a cylindrical SCR housing431for holding the reduction catalyst. In the selective catalytic reducing device430, the oxidation catalyst is provided downstream of the reduction catalyst.

As shown inFIG. 3, the injection valve429is connected to a urea water tank127via pipes (a suction pipe425aand a reducing agent supply pipe425s). The urea water tank127is a container for storing the urea water as the reducing agent. A urea water pump128is provided between the injection valve429in the engine room122E and the urea water tank127in the cooler chamber122C. The urea water pump128is fixed to the partition160inside the cooler chamber122C. The urea water pump128is an electric pump for sucking the urea water in the urea water tank127to convey the urea water to the injection valve429.

The injection valve429shown inFIG. 4injects into the exhaust passage the urea water supplied from the urea water tank127by the urea water pump128. When the urea water is injected, ammonia is generated from the urea water by using the reduction catalyst of the selective catalytic reducing device430, and ammonia causes a reduction reaction of NOx in the exhaust gas, to be decomposed into water and nitrogen. Ammonia in the exhaust gas is reduced by the oxidation catalyst provided downstream of the reduction catalyst in the selective catalytic reducing device430.

As shown inFIGS. 3 and 4, a rear frame220constituting the rear vehicle body120is formed in the shape of a rectangular frame, made up of a pair of right and left longitudinal plates221and a lateral plate222having the front end and the rear end respectively coupled to the pair of right and left longitudinal plates221(the lateral plate at the front end is not shown).

As shown inFIG. 4, the exhaust gas purifying device400is supported by the front-side frame810and the rear-side frame161via a base bracket820being a support structure. The rear-side frame161is fixed to the longitudinal plate221via a bracket221bthat is welded inside each of the pair of right and left longitudinal plates221constituting the rear frame220. The rear side frame161is a gate-shaped support member, and a pair of right and left leg portions162is respectively fitted on the pair of right and left longitudinal plates221. A horizontally and vertically extending support beam163is firmly fixed to the pair of right and left leg portions162. A protruding reception portion163aprotruding forward is provided in the support beam163. As shown inFIG. 3, the tabular partition160described above is fitted on the rear surface of the rear-side frame161by using a fastening member such as a bolt or a nut.

As shown inFIG. 4, the front-side frame810has a similar configuration to that of the rear-side frame161. The front-side frame810is fixed to the pair of right and left longitudinal plates221constituting the rear frame220. The front-side frame810is a gate-shaped support member, and a pair of right and left leg portions812is respectively fitted on the pair of right and left longitudinal plates221. A horizontally and vertically extending support beam813is firmly fixed to the pair of right and left leg portions812. A protruding reception portion813aprotruding rearward is provided in the support beam813. The tabular front plate811is fitted on the front surface of the front-side frame810by using fastening members such as a bolt and a nut.

A front leg838of the base bracket820is mounted in the protruding reception portion813aof the front-side frame810, and a rear leg839of the base bracket820is mounted in the protruding reception portion163aof the rear-side frame161. When the front leg838is fixed to the protruding reception portion813aby using a bolt and a nut and the rear leg839is fixed to the protruding reception portion163aby using a bolt and a nut, the base bracket820is fixed to and supported by the front-side frame810and the rear-side frame161.

As thus described, by the fixation of the exhaust gas purifying device400to the base bracket820and the fixation of the base bracket820to the front-side frame810and the rear-side frame161, the exhaust gas purifying device400is disposed and fixed in a predetermined position above the engine301.

FIG. 5is a view of the engine room122E seen from the left side. InFIG. 5, the housing cover130is omitted. As shown inFIG. 5, the engine hood140covering the engine room122E is provided above the engine301and the exhaust gas purifying device400. The front end of the engine hood140is fitted on the upper end of the front-side frame810, and the rear end of the engine hood140is fitted on the upper end of the rear-side frame161. That is, the front-side frame810and the rear-side frame161are support structures for supporting the engine hood140covering the engine room122E thereabove.

FIG. 6is a perspective view of the housing122seen from left obliquely above. As shown inFIG. 6, an exhaust duct149is provided in a tabular ceiling board141of the engine hood140.FIG. 7Ais a side schematic view of the exhaust duct149, andFIG. 7Bis a plan schematic view of the exhaust duct149. InFIG. 7B, an opening cover142is omitted.FIG. 8is a side schematic view of the exhaust duct149in a disassembled state. The exhaust duct149is an exhaust passage forming element for forming an exhaust passage that discharges the air inside the engine room122E to the outside of the engine room122E, and protrudes upward from the ceiling board141.

As shown inFIGS. 7A and 8, the exhaust duct149has a cover support frame146fitted on an opening144in the ceiling board141and has the opening cover142. The opening cover142is obtained by processing a tabular member to be formed into a bottom-open quadrangular prismatic trapezoidal shape.

As shown inFIG. 7B, a rectangular opening144is provided in the ceiling board141constituting the engine hood140, the opening144having a pair of longer sides along the longitudinal direction and a pair of shorter sides along the horizontal direction. The opening144is provided immediately above the reducing agent injection device420. The cover support frame146in the shape of a rectangular frame, a size larger than the opening144, is provided around the opening144.

As shown inFIGS. 7A, 7B, and 8, the cover support frame146is the support structure for supporting the opening cover142, and includes a pair of right and left longitudinal frames147extending longitudinally and a pair of front and rear lateral frames148extending horizontally. The longitudinal frame147and the lateral frame148are formed by an angle (angle steel) having an L-shape in cross section, a bent steel member, or the like. The longitudinal frame147and the lateral frame148have base portions147b,148bfixed to the periphery of the opening144, and a plurality of support portions147s,148srising from base portions147b,148b. Fitting pieces147a,148aare provided at the tips of the plurality of support portions147s,148s.

The opening cover142is fixed to the fitting pieces147a,148aof the support portions147s,148sby the bolt and the nut. The opening cover142has a larger area than that of the opening144and covers the entire opening144from above. As shown inFIG. 7A, a clearance D is formed between the lower end of the outer periphery of the opening cover142and the upper surface of the ceiling board141.

InFIG. 5, as schematically shown by arrows F, the air in the engine room122E is warmed by the heating elements such as the engine301and the exhaust gas purifying device400and rises, to be introduced into the exhaust duct149. The air introduced into the exhaust duct149passes upward through the inside of the rectangular cover support frame146and flows longitudinally and horizontally along the opening cover142. The air passes through the clearance between the support portions in the cover support frame146and discharged to the outside from the clearance D between the cover support frame146and the ceiling board141.

With reference toFIG. 9, a description will be given of a urea water supply system and a cooling water circulation system of the exhaust gas purifying device400.FIG. 9is a view for describing the urea water supply system and the cooling water circulation system of the exhaust gas purifying device400. The urea water supply system is made up of the urea water pump128, the urea water tank127, and pipes. The urea water pump128and the urea water tank127are connected by the suction pipe425aand a return pipe425b. The urea water pump128and the injection valve429are connected by the reducing agent supply pipe425s. A urea water suction port426ais disposed in the vicinity of the bottom of the urea water tank127in the suction pipe425a, and a urea water discharge port426bis disposed in the vicinity of the top of the urea water tank127in the return pipe425b. Urea water sucked from the bottom of the urea water tank127by the urea water pump128is supplied into the reducing agent supply pipe425sand pressurized. The urea water in the reducing agent supply pipe425sis injected and supplied to the exhaust passage of the engine301by opening of the injection valve429. An excess of the urea water is returned to the urea water tank127via the return pipe425b.

The exhaust gas purifying device400includes the cooling water circulation system in order to prevent deterioration in quality of urea water due to an increase in temperature of the urea water. The cooling water circulation system is a system made up of a cooling water pump, not shown, a pipe, and valves, and guiding cooling water (engine cooling water) to the urea water tank127and the injection valve429to cause the cooling water and the urea water exchange heat. The cooling water circulation system includes an engine cooling system880, and a refrigerant pipe881for guiding the cooling water from the engine cooling system880to the urea water tank127and the injection valve429.

The engine cooling system880cools the engine301by supplying the engine301with the cooling water cooled by the radiator504. The engine301is provided with a thermostat305and a cooling water pump (not shown) for circulating the engine cooling water. The thermostat305opens or closes a route of the engine cooling system880between a fully closed state and a fully opened state in accordance with the temperature of the engine cooling water.

Although not shown, in the engine, a bypass route that bypasses the engine cooling water so as not to supply the engine cooling water to the radiator504is provided when the thermostat305fully closes the route. When the temperature of the engine cooling water is low at the start of the engine, the engine cooling water circulates in the engine and is warmed due to heat generation of the engine301.

The refrigerant pipe881through which the cooling water flows has a first refrigerant pipe435that is set up so as to pass through the injection valve429and a second refrigerant pipe437that is set up so as to pass of the urea water tank127. The first refrigerant pipe435has a first supply pipe435sfor guiding the cooling water to the injection valve429and a first return pipe435rfor returning the engine cooling water from the injection valve429to the engine301. The second refrigerant pipe437has a second supply pipe437sfor guiding the cooling water to the urea water tank127and a second return pipe437rfor returning the cooling water from the urea water tank127to the engine301. The second refrigerant pipe437is provided with a switching valve437vthat is switched between the fully closed state and the fully opened state in accordance with a control signal from the control device, not shown.

With reference toFIG. 3, the pipes around the urea water tank will be described. As shown inFIG. 3, each of the suction pipe425aand the return pipe425bis inserted from the upper surface of the urea water tank127into the urea water tank127. The suction pipe425aand the return pipe425bare connected by the urea water pump128fitted on the partition160. The reducing agent supply pipe425s, through which the urea water discharged from the urea water pump128flows, is guided to the engine room122E via the opening in the partition160and connected to the injection valve429(cf.FIG. 5).

The second supply pipe437sconstituting the second refrigerant pipe437is guided from the engine room122E to the cooler chamber122C via the opening in the partition160, to be inserted from the upper surface of the urea water tank127into the urea water tank127. The second return pipe437rconstituting the second refrigerant pipe437is guided from the upper surface of the urea water tank127to the outside of the urea water tank127and further guide to the engine room122E via the opening in the partition160, to be connected to the engine301. That is, the second refrigerant pipe437through which the engine cooling water flows is set up so as to pass through the urea water tank127.

With reference toFIG. 5, the pipes around the reducing agent injection device will be described. As shown inFIG. 5, the refrigerant pipe881is guided from the engine301to the partition160along the base bracket820and branched into the first refrigerant pipe435and the second refrigerant pipe437. The second refrigerant pipe437is guided to the cooler chamber122C via the opening in the partition160.

The first supply pipe435sconstituting the first refrigerant pipe435is guided upward along the partition160and further guided front obliquely upward to the rear portion of the exhaust duct149. The first supply pipe435sis bent in the exhaust duct149and guided front obliquely downward to the front portion of the exhaust duct149. The first supply pipe435sis turned back below the front portion of the exhaust duct149and guided rear obliquely downward to the injection valve429, to be connected to the injection valve429.

The first return pipe435rconstituting the first refrigerant pipe435is guided front obliquely upward from the injection valve429and turned back in the vicinity of the injection valve429, and is then guided rear obliquely downward along the DRT housing421. The first return pipe435ris bent downward in the vicinity of the partition160and connected to the engine301.

The reducing agent supply pipe425sis guided from the opening in the partition160to the engine room122E and routed in the state of being brought close to or into contact with the first supply pipe435sby a similar route to that of the first supply pipe435s. By routing the reducing agent supply pipe425sand the first supply pipe435sin the state of being brought close to or into contact with each other, the temperature of the urea water can be held appropriate through the heat exchange between the urea water and the cooling water in the reducing agent supply pipe425s.

The reducing agent supply pipe425sis guided front obliquely upward to the rear portion of the exhaust duct149along with the first supply pipe435s. The reducing agent supply pipe425sis bent in the exhaust duct149and guided front obliquely downward to the front portion of the exhaust duct149. The reducing agent supply pipe425sis turned back below the front portion of the exhaust duct149and guided rear obliquely downward to the injection valve429, to be connected to the injection valve429.

Meanwhile, the cooling water pump (not shown) for circulating the cooling water is driven by the engine301. Therefore, when the engine301stops, the cooling water pump also stops and the circulation of the cooling water thus stops. However, radiation heat is radiated from the engine301even after the engine has stopped, and hence the injection valve429needs to be cooled even after the engine has stopped.

The present embodiment is configured such that the first supply pipe435sconnected to the injection valve429is provided above the injection valve429and the cooling water remains (is reserved) in the pipe even after stopping of the engine.

FIG. 10is a view for describing a reservoir area RA of the first supply pipe435sand the reducing agent supply pipe425s. In the present embodiment, each of regions from a top portion TP of the center of the tubes (first supply pipe435sand reducing agent supply pipe425s) to connection portions (CP1, CP2) between the pipes (first supply pipe435sand reducing agent supply pipe425s) and the injection valve429is defined as a reservoir area RA. The reservoir area RA is disposed between the reducing agent injection device420and the exhaust duct149.

A vertical dimension (height dimension) H1of the reservoir area RA of the first supply pipe435sis set to about 150 mm to 200 mm. Similarly, a vertical dimension (height dimension) H2of the reservoir area RA of the reducing agent supply pipe425sis set to about 150 mm to 200 mm. Thereby, the cooling water and the urea water are reserved in the reservoir areas RA indicated by hatching. Providing the reservoir area RA of the first supply pipe435senables prevention of damage on the sealing member, the pipe, and the like due to the remaining heat of the engine301after stopping of the engine.

As shown inFIG. 5, in the present embodiment, the top portion TP of the first supply pipe435sand the reducing agent supply pipe425sis located inside the exhaust duct149and above the upper surface of the ceiling board141. As shown in the figure, a longitudinal length L1of the reservoir area RA is smaller than a longitudinal length L2of the opening144. The first supply pipe435sand the reducing agent supply pipe425sare routed such that the entire reservoir areas RA of the first supply pipe435sand the reducing agent supply pipe425sare held inside the opening144in plan view.

Each pipe is made of a hose having flexibility, a bracket and a metal fitting for routing each pipe are provided in each of the constituent members such as the engine hood140, the rear-side frame161, and the partition160, and each pipe is supported in a predetermined position by using the bracket and the metal fitting for routing.

As described above, the air warmed inside the engine room122E (cf.FIGS. 1 to 3) rises to be discharged to the outside of the engine room122E via the exhaust duct149. At this time, due to placement of the top portion TP and the reservoir areas RA of the first supply pipe435sand the reducing agent supply pipe425son a route (on a flow passage) for a flow F (cf. schematic arrows shown inFIG. 5) generated by natural convection, it is possible to effectively cool the cooling water and the urea water that are reserved in the reservoir areas RA after stopping of the engine.

According to the embodiment described above, the following effects can be obtained:

(1) The wheel loader is provided with the exhaust gas purifying device400including: the selective catalytic reducing device430that performs treatment on exhaust gas of the engine301; and the reducing agent injection device420that injects urea water into exhaust gas to be supplied to the selective catalytic reducing device430. The wheel loader includes the housing122that delimits the engine room122E accommodating the engine301and the exhaust gas purifying device400. The housing122includes the engine hood140constituting the top board that covers the engine room122E above the engine301, and the exhaust duct149that is provided in the engine hood140and discharges the air in the engine room122E to the outside of the engine room122E. The reducing agent supply pipe425sthat guides the urea water is connected to the reducing agent injection device420. A part (the top portion TP) of the reducing agent supply pipe425sextending upward from the reducing agent injection device420is disposed in the exhaust duct149in the position above the reducing agent injection device420.

In the present embodiment, the exhaust duct149includes the opening cover142that covers the upper side of the opening144in the ceiling board141of the engine hood140and is disposed opposing to the upper surface of the ceiling board141with a clearance therebetween, and the cover support frame146for supporting the opening cover142. The top portion TP of the reducing agent supply pipe425sis located above the upper surface of the ceiling board141.

Hence it is possible to cool the reducing agent supply pipe425sby the flow of the air that is warmed and rises in the engine room122E and is discharged from the exhaust duct149. It is thus possible to prevent an increase in temperature of the urea water inside the reducing agent supply pipe425s, and thereby to prevent deterioration in quality of the urea water.

Although the exhaust gas purifying device400stops the supply of the urea water in accordance with the stopping of the engine301, if the reducing agent remains in the reducing agent injection device420or the reducing agent supply pipe for supplying urea water, moisture evaporates due to the remaining heat therearound and urea is deposited, which might cause the occurrence of clogging in the reducing agent supply pipe425sand the reducing agent injection device420. In the present embodiment, it is possible to prevent an increase in temperature of the urea water in the reducing agent supply pipe425s, and thereby to prevent clogging of the reducing agent injection device420.

(2) The part of the first supply pipe435sfor guiding the cooling water of the engine301to the reducing agent injection device420is disposed in the exhaust duct149in the position above the reducing agent injection device420. Similarly to the reducing agent supply pipe425s, routing the supply pipe (first supply pipe435s) for cooling water can prevent an increase in temperature of the cooling water reserved in the first supply pipe435safter stopping of the engine301, enabling effective cooling of the reducing agent injection device420by using the cooling water. This can lead to prevention of damage on the sealing member and the pipe (hose) in the connection portion of the reducing agent injection device420.

(3) The exhaust duct149is located immediately above the reducing agent injection device420. Between the reducing agent injection device420and the exhaust duct149, the reservoir area RA is disposed which extends from the respective connection portions of the reducing agent injection device420with the reducing agent supply pipe425sand the first supply pipe435sto the top portion TP. Hence it is possible to effectively cool the entire reservoir area RA due to the flow of the air generated by natural convection.

Modifications as below are also within the scope of the present invention, and one or more of modifications can be combined with the embodiment described above.

In the embodiment described above, the examples where the first supply pipe435sis made up of the hose alone has been described, but the present invention is not limited thereto. As indicated by two-dot chain lines ofFIG. 10, a reservoir portion900may be disposed in the hose so that the first supply pipe435smay include the hose and the reservoir portion900. The reservoir portion900has a larger cross sectional area of the flow passage than the cross sectional area of the flow passage of the hose, and is provided for the purpose of expanding the volume of the cooling water. Disposing the reservoir portion900in the exhaust duct149enables effective cooling of the cooling water in the reservoir portion900.

In the embodiment described above, the cooling water circulation system is provided so as to prevent an increase in temperature of the urea water, but the cooling water circulation system may be used for thawing frozen urea water. When crane operation is performed in a cold region or in winter, if urea water is frozen, the reducing agent injection device420cannot supply the urea water. Hence the use of the reducing agent injection device420requires thawing of the frozen urea water and further requires prevention of the urea water from being frozen again. Accordingly, the cooling water warmed by heat exchange with the engine301is guided to the injection valve429and the urea water tank127, to enable thawing of the frozen urea water and prevention of the urea water from being frozen again.

In the embodiment described above, the example where the urea aqueous solution is used as the reducing agent has been described, but the present invention is not limited thereto. The present invention is applicable to a work machine provided with the exhaust gas purifying device400using a variety of reducing agents such as an ammonia aqueous solution.

In the embodiment described above, the example where the present invention is applied to the wheel loader has been described, but the present invention is not limited thereto and applicable to a variety of work machines such as a hydraulic shovel or a crane.

Although the variety of embodiments and modifications have been described above, the present invention is not limited to the description of those. Other aspects conceivable within the scope of the technical idea of the present invention are also included in the scope of the present invention.

REFERENCE SIGNS LIST