Work vehicle

Abstract

To provide a work vehicle capable of smoothly treating residual ammonia in a SCR device and successfully preventing ammonia slip.SOLUTION: A work vehicle includes an exhaust emission control device M that treats an exhaust gas discharged from an engine E for purification. A DPF device 30 for removing particulate matters in the exhaust gas, a urea mixing pipe 35 for injecting urea water to the exhaust gas for mixing in the pipe and a SCR device 40 for removing nitrogen oxide are provided in the exhaust emission control device M from the upstream side in this order. The SCR device 40 includes: a SCR case 41 coupled to the terminal of the urea mixing pipe 35; a SCR catalyst and an ammonia oxidation catalyst disposed in the SCR case 41; and a discharge pipe 44 coupled to the outlet portion of the SCR case 41. The discharge pipe 44 includes ammonia discharge suppression means for suppressing discharge of ammonia. As the ammonia discharge suppression means, a heating wire for heating inside of the discharge pipe and a discharge valve for raising the exhaust pressure are provided.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present invention relates to a work vehicle equipped with an exhaust gas purification device that purifies exhaust gas. [Background technology]

[0002] Conventionally, there is known a work vehicle equipped with an exhaust gas purification device for treating and purifying exhaust gas discharged from an engine (see, for example, Patent Document 1 below). This exhaust gas purification device is configured to include a DPF (Diesel particulate filter) device that removes particulate matter from exhaust gas, and an SCR (Selective Catalytic Reduction) device that removes NOx.

[0003] Here, the SCR device is The system is equipped with a urea water injection unit that injects urea water, and an SCR catalyst. The urea water injection unit injects urea water into the path through which exhaust gas passes. The urea contained in the urea water is hydrolyzed into ammonia when it comes into contact with high-temperature exhaust gas. The SCR catalyst is made of materials such as zeolite and ceramics that adsorb ammonia. NOx (nitrogen oxides) contained in exhaust gas are reduced when they come into contact with the SCR catalyst that has adsorbed ammonia, and are converted into nitrogen and water. This is a mechanism that reduces NOx emissions. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2016-160908 A Summary of the Invention [Problem to be solved by the invention]

[0005] However, in SCR devices, the remaining ammonia not used in reduction is discharged into the outside air, i.e., ammonia slip may occur. In some cases, an oxidation catalyst is provided downstream of the SCR catalyst to treat this residual ammonia, but if there is a large amount of residual ammonia, the treatment may be insufficient. Therefore, the present invention provides a work vehicle that can solve such problems and effectively prevent ammonia slip by smoothly treating the residual ammonia in the SCR device. [Means for solving the problem]

[0006] In order to achieve the above object, the first invention provides: A work vehicle equipped with an exhaust gas purification device that processes and purifies exhaust gas discharged from an engine, The exhaust gas purification device includes, in order from the upstream side, a DPF device that removes particulate matter from exhaust gas, a urea mixing tube that injects urea water into exhaust gas and mixes it inside the tube, and an SCR device that removes nitrogen oxides, The SCR device includes an SCR case connected to an end of the urea mixing pipe, an SCR catalyst and an ammonia oxidation catalyst disposed in the SCR case, and an exhaust pipe connected to an outlet portion of the SCR case, The exhaust pipe is provided with an ammonia emission suppression means for suppressing the emission of ammonia, The work vehicle is characterized in that, as the ammonia emission suppression means, an electric heating wire for heating the inside of the exhaust pipe and an exhaust valve for increasing the exhaust pressure of the exhaust pipe are provided.

[0007] According to the first aspect of the present invention, the inside of the tube is heated to evaporate the residual ammonia, thereby preventing ammonia slip, while the discharge of ammonia can be suppressed by the discharge valve that increases exhaust pressure.

[0008] The second invention has the same configuration as the first invention, as well as: The SCR case is characterized in that a swirl generating plate having a spirally formed flat plate is provided on the inner wall of the SCR case.

[0009] According to the second invention, in addition to the effects of the first invention, a swirl (a vortex formed by the working fluid) is generated by the swirl generating plate, and a stirring effect is obtained, thereby increasing the reaction of the urea water and more effectively preventing ammonia slip.

[0010] The third invention has the same configuration as the first invention, as well as: The SCR case is characterized in that it is arranged vertically with its longitudinal direction extending up and down.

[0011] According to the third invention, in addition to the effects of the first invention, the SCR case is vertically oriented with its longitudinal direction in the up-down direction, which causes the residual ammonia to flow downward and become less likely to be discharged, thereby more effectively preventing ammonia slip.

[0012] The fourth invention is, in addition to the configuration of the third invention, The ammonia emission suppression means is further characterized in that an oxidizer injection unit that injects an oxidizer into the exhaust pipe is provided.

[0013] According to the fourth invention, in addition to the effects of the third invention, the oxidizer injection unit oxidizes the residual ammonia in the tube, thereby preventing ammonia slip. Also, since the SCR case is arranged vertically, a part of the oxidizer injected by the oxidizer injection unit is supplied to the ammonia oxidation catalyst in the SCR case, thereby further promoting the oxidation of ammonia and more effectively preventing ammonia slip.

[0014] The fifth invention is, in addition to the configuration of the third invention, A support and fixing base is provided to support and fix the bottom of the SCR case, The support and fixing seat is characterized in that it is cantilevered between a cabin side bracket fixed to the cabin of the work vehicle and a vehicle side bracket fixed to the vehicle body with an elastic body interposed therebetween.

[0015] According to the fifth aspect of the invention, in addition to the effects of the third aspect of the invention, since the upper part of the SCR device is easily vibrated due to the vertical arrangement of the SCR case, the support and fixing seat that supports and fixes the bottom part of the SCR case is cantilevered with an elastic body between them, so that wear failures due to vibration can be effectively prevented. As a result, the occurrence of ammonia slip due to wear of the device can also be effectively prevented.

[0016] The sixth invention is, in addition to the configuration of any one of the first to fifth inventions, a urea water injection unit disposed in the urea mixing tube and configured to inject urea water; A control unit that controls the injection of the urea injection unit; an exhaust gas temperature sensor for detecting the temperature of exhaust gas discharged from the engine; An SCR catalyst temperature detection sensor for detecting a temperature of the SCR catalyst, The control unit acquires detection information from the exhaust temperature sensor and the SCR catalyst temperature detection sensor, and controls the urea injection unit to perform injection on the condition that the detection value of the exhaust temperature sensor is equal to or greater than a first set value; and The present invention is characterized in that the injection of the urea injection unit is controlled to be stopped when the detection value of the exhaust gas temperature sensor falls below a first set value and the detection value of the SCR catalyst temperature detection sensor falls below a second set value.

[0017] According to the sixth aspect of the present invention, in addition to the effects of any one of the first to fifth aspects of the present invention, When the SCR catalyst is in an activated state, the urea water injection unit continues to inject urea water. Therefore, even if the exhaust temperature temporarily drops due to, for example, an operator intermittently pressing the accelerator pedal, the injection of urea water can be continued, thereby reducing nitrogen oxide emissions. Effect of the Invention

[0018] According to the present invention, it is possible to provide a work vehicle that can smoothly process residual ammonia in an SCR device and effectively prevent ammonia slip. [Brief description of the drawings]

[0019] [Figure 1] FIG. 1 is a left side view of a work vehicle according to a preferred embodiment of the present invention. [Diagram 2] FIG. 2 is a plan view of the same. [Diagram 3] FIG. 3 is a perspective view showing the configuration of the engine and its surroundings as viewed from the left rear side; [Figure 4] FIG. 4 is a front view showing the configuration of the engine and the exhaust gas purification device. [Diagram 5] FIG. 5 is a right side view showing the configuration around the engine. [Figure 6] FIG. 6 is an explanatory diagram showing a schematic diagram of intake and exhaust flows in the configuration around the engine. [Figure 7] FIG. 7 is a schematic front view of the essential parts showing the layout configuration of the SCR case. [Figure 8] FIG. 8 is a block diagram showing the configuration of a control unit that controls each mechanism of the work vehicle. [Figure 9] FIG. 9 is a flowchart relating to the control of the urea water injection unit. [Figure 10] FIG. 10 is a diagram showing a urea water injection amount map for determining the urea water injection amount. [Figure 11] 11(a) to 11(c) are explanatory diagrams for explaining the injection pattern of the urea water. [Figure 12] FIG. 12 is a flowchart relating to control of a urea water injection unit in another embodiment. [Figure 13] FIG. 13 is a flowchart relating to control of a urea water injection unit in another embodiment (2). [Figure 14] FIG. 14 is a schematic diagram showing the layout of a urea water tank according to another embodiment (3). [Figure 15] FIG. 15 is a schematic diagram showing the layout of a urea water tank according to another embodiment (4). [Figure 16] FIG. 16 is a schematic diagram showing the layout of a urea water tank according to another embodiment (5). [Figure 17]FIG. 17 is a schematic diagram showing the configuration of a blower turbine according to a modified example. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] <1. Overall configuration of the work vehicle> Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. FIG. 1 is a left side view of a work vehicle according to a preferred embodiment of the present invention, and FIG. 2 is a plan view. A work vehicle 1 according to a preferred embodiment of the present invention is configured as a so-called tractor, but is not limited to this and can also be configured as other work vehicles (for example, a skid steer loader, etc.).

[0021] The work vehicle 1 is equipped with a vehicle body 1a for traveling forming the machine frame, front wheels 2, rear wheels 3, an engine E as a power source, and a transmission 5. Of these, the front wheels 2 are provided mainly as steering wheels, i.e., as steering wheels. The rear wheels 3 are provided mainly as driving wheels, i.e., as driving wheels. Rotational power generated by an engine E mounted inside a bonnet 6 at the front of the machine body can be transmitted to the rear wheels 3 after being appropriately reduced in speed by a transmission in a transmission case 5, and the rear wheels 3 generate driving force by this rotational power. In addition, an exhaust gas purification device M that processes exhaust gas discharged from the engine E is provided near the engine E.

[0022] The transmission 5 can transmit the rotational power generated by the engine E to the front wheels 2 as well, as necessary. In this case, the front wheels 2 and the rear wheels 3 are the four drive wheels, generating a driving force. That is, the transmission 5 can switch between two-wheel drive and four-wheel drive, and can reduce the rotational power of the engine E and transmit the reduced rotational power to the front wheels 2 and the rear wheels 3. The tractor 1 is also provided with a coupling device 7 at the rear of the vehicle body to which a working machine such as a rotary (not shown) can be attached. The coupling device 7 is, for example, a three-point link consisting of a top link 7a at the center upper part and lower links 7b, 7b at the left and right lower parts, and connects the working machine to the rear of the vehicle body of the tractor 1. The tractor 1 can raise and lower the working machine via a lift rod and the lower link 7b connected to the lift rod by hydraulically rotating the left and right lift arms as described later.

[0023] The cockpit 8 on the aircraft body is surrounded by a cabin 9. This cabin 9 is disposed on the upper part of the vehicle body 1a, and inside the cabin 9, a steering wheel 11 is provided standing on a dashboard 10 in front of the cockpit 8, and various operation pedals such as a clutch pedal, a brake pedal, an accelerator pedal, etc., and various operation levers such as a forward / reverse lever, a gear shift lever, etc. are disposed around the cockpit 8.

[0024] An exhaust muffler 4 that discharges exhaust gas from the engine E to the outside of the aircraft is disposed on the front right side of the cabin 9, and a urea water tank 36c and a fuel tank Et are disposed below the cabin 9. As will be described later, the urea water tank 36c is connected to a urea water injection nozzle 47a by a urea water injection pipe 47b.

[0025] <2. Engine configuration> Next, the configuration of the engine periphery (engine E and exhaust gas purification device M) will be described. FIG. 3 is an oblique view showing the configuration around the engine as viewed from the rear left side, FIG. 4 is a front view showing the configuration around the engine, FIG. 5 is a right side view showing the configuration around the engine, and FIG. 6 is an explanatory diagram showing a schematic diagram of the intake and exhaust flows in the configuration around the engine.

[0026] The engine E is, for example, a diesel engine. As shown in Figs. 3 to 5, the engine E has an external configuration in which a cylinder head 20b and a cylinder cover 20c are provided on the upper part of a cylinder block 20a, and an oil pan 21 is provided on the lower part of the cylinder block 20a. The engine E also has a cooling fan rotation mechanism 22 for rotating a cooling fan (not shown) on the front part of the cylinder block 20a, and a flywheel case 23 in which a flywheel (not shown) connected to a crankshaft is disposed on the lower rear part of the cylinder block 20a. The cylinder block 20a has a plurality of cylinders arranged so that a plurality of pistons connected to the crankshaft reciprocate therein.

[0027] 6, the internal configuration of the engine E includes, as intake system members, an intake section 24a, a supercharger 24b, an intake throttle (intake throttle device) 24c, and an intake manifold 24d. The gas sucked in through the intake section 24a is compressed by the supercharger 24b and then supplied to the intake manifold 24d via the intake throttle 24c.

[0028] A common rail (not shown) is disposed below the intake manifold 24d. The common rail stores fuel at high pressure and supplies it to injectors 25 (fuel injection devices) disposed in the cylinder head 20b.

[0029] The injector 25 includes an injector electromagnetic valve 25a (see FIG. 8). The injector electromagnetic valve 25a opens and closes at a timing according to an instruction from the ECU 50 to inject fuel into the combustion chamber.

[0030] 3 to 6, the engine E is equipped with an engine speed sensor S1 that detects the engine speed (rotation speed r / min, number of rotations of the crankshaft per predetermined time) and an engine output sensor S2 that detects the engine output Le (kW) (see FIG. 8). The engine speed sensor S1 and the engine output sensor S2 output the detected engine speed and engine output to the ECU 50.

[0031] The engine E also includes an exhaust manifold 26. A portion of the gas passing through the exhaust manifold 26 is supplied to an EGR device 27, and the remainder is supplied to an exhaust gas purification device M. The EGR device 27 includes an EGR cooler 27a, an EGR pipe 27b, and an EGR valve 27c. The opening degree of the EGR valve 27c is controlled by the ECU 50.

[0032] <2. Configuration of exhaust gas purification device (DPF device)> Next, the exhaust gas purification device M will be described with reference to Fig. 6. Exhaust gas discharged through the exhaust manifold 26 of the engine 3 passes through the exhaust turbine section 24e of the turbocharger 24b and is taken in from an exhaust connection pipe 28. The exhaust gas purified by the exhaust gas purification device M is discharged outside the aircraft through the exhaust muffler 4 (see Fig. 1).

[0033] The exhaust gas purification device M includes, in this order from the upstream side of the exhaust gas, a DPF device 30 and an SCR device 40. Note that some devices and members of the DPF device 30 and the SCR device 40 shown in Fig. 6 are omitted in Figs. 3 to 5.

[0034] The DPF device 30 functions to collect and remove particulate matter (PM) contained in exhaust gas. The DPF device 30 includes a DPF case 31, a PM oxidation catalyst 32, and a filter 33.

[0035] The DPF case 31 is a substantially cylindrical hollow member, and has a PM oxidation catalyst 32 and a filter 33 disposed therein. The PM oxidation catalyst 32 is made of platinum or the like, and is a catalyst for oxidizing (burning) unburned fuel, carbon monoxide, nitrogen monoxide, etc. contained in the exhaust gas. The filter 33 is configured as, for example, a wall-flow type filter, and collects particulate matter contained in the exhaust gas treated by the oxidation catalyst 32.

[0036] The exhaust gas that has passed through the DPF device 30 is sent to the SCR device 40 via a urea mixing pipe 35 (mixing piping). Here, the urea mixing pipe 35 is equipped with a urea water injection unit 36 ​​that injects urea water into the exhaust gas inside the pipe, a water injection unit 37 that injects water into the pipe, an air turbine 38 that reduces the exhaust pressure, and a mixer unit 39 that mixes the air flow inside the pipe.

[0037] The urea water injection unit 36 ​​includes a urea water injection nozzle 36a for injecting urea water, a urea water pump 36b, and a urea water tank 36c. The urea water pump 36 is driven to inject the urea water stored in the urea water tank 36c from the urea water injection nozzle 36a. By injecting the urea water into the urea mixing tube 45, urea is hydrolyzed to generate ammonia. The urea water injection unit 36 ​​is controlled by a DCU (Dosing Control Unit) 60 to determine whether or not to inject urea water and the injection amount. The DCU 95 starts injecting urea water when, for example, the temperature of the exhaust gas exceeds a temperature at which urea is hydrolyzed into ammonia.

[0038] The water injection unit 37 includes a water injection nozzle 37a for injecting water, a water pump 37b, and a water tank 37c. The water pump 36b is driven to inject water stored in the water tank 36c from the water injection nozzle 36a. The water injection nozzle 37a is disposed so as to face the tip of the urea water injection nozzle 36a, and injects water toward the urea water injection nozzle 36a. If the urea water crystallizes, the tip of the urea water injection nozzle 36a cannot spray the urea water. Therefore, crystallization can be prevented by periodically spraying water at a predetermined time interval using the water injection unit 37. The water injection nozzle 37a is disposed at an inclination (about 45° with respect to the longitudinal direction of the piping), so that the water can be sprayed well toward the tip of the urea water injection nozzle 36a. By shifting the front-rear arrangement positions of the urea water injection nozzle 36a and the water injection nozzle 37a, the urea water is prevented from adhering to the water injection nozzle 37a and crystallizing. The water ejection unit 37 is controlled by the DCU 60 as to whether or not to eject water and the amount of water ejected.

[0039] The blower turbine 38 is disposed inside the urea mixing pipe 35 and is a blower that blows air by rotating turbine-shaped blades using an electric motor. Driving this blower turbine 38 reduces the exhaust pressure and promotes exhaust from the DPF device 30.

[0040] The mixer section 39 rotates a mixer equipped with stirring blades to stir the airflow within the pipe, thereby promoting mixing through turbulence.

[0041] <3. Configuration of exhaust gas purification device (SCR device)> The SCR device 40 receives the exhaust gas from the urea mixing pipe 35, and functions to remove NOx contained in the exhaust gas. The SCR device 40 includes an SCR case 41, an SCR catalyst 42, an ammonia oxidation catalyst 43, and an exhaust pipe 44.

[0042] The SCR case 41 is a substantially cylindrical hollow member, and contains an SCR catalyst 42 and an ammonia A near-oxidation catalyst 43 is provided. The SCR catalyst 42 is made of materials such as zeolite and ceramics that adsorb ammonia. The ammonia generated by the urea water injection unit 36 ​​injecting the urea water is adsorbed by the SCR catalyst 42. NOx contained in the exhaust gas is reduced by coming into contact with the SCR catalyst 42 that has adsorbed ammonia, and is converted into nitrogen and water.

[0043] Here, the SCR case 41 is arranged vertically with the vertical direction as the longitudinal direction, and is configured to effectively prevent ammonia slip by making the residual ammonia flow downward and difficult to be discharged. Also, on the inner wall of the SCR case 41, a swirl generating plate 41a having a flat plate formed in a spiral shape is provided in front of (upstream of) the SCR catalyst 42 so as to extend from the inner wall. This swirl generating plate 41a generates a swirl (a vortex formed by the working fluid) and obtains a stirring effect, thereby increasing the reaction of the urea water and more effectively preventing ammonia slip.

[0044] The ammonia oxidation catalyst 43 is a catalyst that prevents ammonia that has been desorbed from or not adsorbed by the SCR catalyst 42 from being released to the outside. The ammonia oxidation catalyst 43 is an oxidation catalyst such as platinum that oxidizes ammonia, and oxidizes the ammonia to change it into nitrogen, carbon monoxide, water, etc. After passing through the ammonia oxidation catalyst 43, the exhaust gas passes through the exhaust pipe 44 and is released to the outside from the exhaust muffler 4.

[0045] In addition, an SCR catalyst temperature sensor S3 is attached near the SCR catalyst 42. The SCR catalyst temperature sensor S3 detects the temperature of the SCR catalyst 42 and outputs the temperature to the DCU 60.

[0046] Furthermore, in order to detect the NOx concentrations upstream and downstream, a NOx concentration sensor S5 is attached to the inlet portion of the DPF case 31 and the outlet portion of the SCR case 41, respectively. The NOx concentration detected by this NOx sensor S5 can be mainly used to determine the injection interval of the urea water. Furthermore, an exhaust temperature sensor S4 is provided at the outlet portion of the DPF case 31 to detect the exhaust temperature, which is the temperature of the exhaust gas discharged from the engine E. Note that the position of the exhaust temperature sensor S4 is not limited to the illustrated example, and it may be provided at any appropriate position where the temperature of the exhaust gas discharged from the engine E can be detected.

[0047] The starting end of the exhaust pipe 44 is connected to the outlet portion of the SCR case 41, and the terminal end is connected to the exhaust muffler 4, and serves to send the exhaust gas that has passed through the SCR device 40 to the exhaust muffler 4. The exhaust pipe 44 is equipped with an oxidizer injection unit 45, a heating wire 46, and an exhaust valve 47, in this order from the upstream side of the exhaust gas.

[0048] The oxidizer injection unit 45 includes an oxidizer injection nozzle 45a for injecting an oxidizer, an oxidizer pump 45b, and an oxidizer tank 45c, and the oxidizer pump 45 is driven to inject the oxidizer stored in the oxidizer tank 45c from the oxidizer injection nozzle 45a. This oxidizes the residual ammonia in the pipe, and prevents ammonia slip. In addition, since the SCR case 61 is vertically disposed, a portion of the oxidizer injected by the oxidizer injection nozzle 45a is supplied to the ammonia oxidation catalyst 43, which promotes the oxidation of ammonia and more effectively prevents ammonia slip.

[0049] The heating wire 46 is disposed on the inner wall of the exhaust pipe 44, and heats the inside of the pipe to evaporate the residual ammonia and prevent ammonia slip. This allows the residual ammonia in the SCR device 40 to be processed smoothly. The exhaust valve 47 is a valve whose opening and closing is controlled by the ECU 50, and the more the valve is closed, the more the exhaust pressure in the pipe (and the SCR device 40) can be increased, thereby suppressing the emission of ammonia.

[0050] FIG. 7 is a schematic front view of the essential parts showing the arrangement of the SCR case 41. As shown in FIG. As shown in FIG. 7, the support fixing seat 48 that supports and fixes the bottom of the SCR case 41 is cantilevered and clamped by a cabin side bracket 49a fixed to the cabin 9 and a vehicle side bracket 49b fixed to the vehicle body 1a by bolt fastening. Furthermore, a soft rubber g1 (soft elastic body) is interposed between the cabin side bracket 49a and the vehicle side bracket 49b, and a hard rubber g2 (hard elastic body) is interposed between the cabin side bracket 49a and the vehicle side bracket 49b. This improves the cushioning effect by the soft rubber g1, and prevents wear failure by the hard rubber g2. Furthermore, as shown in the figure, it is preferable that the end portion of the urea mixing pipe 35 is flexible piping to prevent vibration from being transmitted from the engine E to the SCR device 40. With the above configuration, it is possible to suitably prevent vibration of the SCR device 40. In particular, since the SCR case 41 is vertically arranged, the upper part of the SCR device 40 is easily vibrated, and the above configuration can suitably prevent wear failure due to vibration.

[0051] <4. Configuration of the control unit> FIG. 8 is a block diagram showing the configuration of a control unit C that controls each mechanism of the work vehicle 1. As shown in FIG. 8, the control unit C includes an ECU (Engine Control Unit) 50 and a DCU (Dosing Control Unit) 60. The ECU 50 and the DCU 60 each include a calculation unit including a CPU or the like, and a storage unit including a ROM, a RAM, or the like. The calculation unit is capable of controlling each mechanism by sending control commands to various actuators in the actuator group based on information from various sensors in the sensor group, and the storage unit stores various programs and control information required for control.

[0052] As shown in FIG. 7, the input side of the control unit C is connected to a group of sensors including an engine speed sensor S1, an engine output sensor S2, an SCR catalyst temperature sensor S3, an exhaust temperature sensor S4, and a NOx concentration sensor S5, and the output side of the control unit C is connected to the ECU 50 to a group of actuators including an injector solenoid valve 25a, an EGR valve 27a, an intake throttle 24c, an exhaust valve 47, an air blower turbine 38, and a mixer unit 39, and the actuators are connected to the ECU 50, and the urea water injection unit 36, the water injection unit 37, and the oxidizer injection unit 45 are connected to the DCU 60.

[0053] <5. Control of urea water injection unit> Next, the control of the urea water injection unit by the control unit C will be described with reference to FIGS. Fig. 9 is a flowchart relating to the control of the urea water injection unit, Fig. 10 is a diagram showing a urea water injection amount map for determining the urea water injection amount, Fig. 11 is an explanatory diagram for explaining the injection interval of the urea water.

[0054] As shown in Fig. 9, when the engine E is running, the control unit C acquires detection information from the exhaust temperature sensor S4 and monitors the detected value of the exhaust temperature (step #1). When the exhaust temperature becomes equal to or higher than a first set value, the control unit C acquires detection information from the engine speed sensor S1 and the engine output sensor S2, and determines the injection amount according to the urea water injection amount map shown in Fig. 10 based on the detected values ​​of the engine speed and the engine output, and controls the urea water injection unit 36 ​​to inject the urea water (step #2). Here, the first set value is set to a predetermined exhaust temperature value that is appropriate from the viewpoint of reaction for the urea water injection unit 36 ​​to inject the urea water.

[0055] As shown in Fig. 10, the injection amount is determined by the detected values ​​of engine speed (r / min) and engine output (kW). That is, the urea water injection amount map is, for example, as shown in the figure, a map in which the vertical axis is engine output (kW) and the horizontal axis is engine speed (r / min), and a set value of the injection amount is stored for each point on the map, and one point on the urea water injection amount map is determined by the detected values ​​of engine speed (r / min) and engine output (kW), and the injection amount is determined to be the set value at that point. Also, as shown in the figure, the set value of the injection amount in the urea water injection amount map is configured so that the injection amount increases in proportion to the increase in engine output, but in the same engine output band, the injection amount is configured to gradually increase as the engine speed increases. Note that the numerical value of the injection amount shown in the figure indicates, for example, the injection amount injected in one (or one) injection from the urea water injection unit 36.

[0056] Moreover, the control unit C determines an injection pattern of the urea water and performs injection of the urea water. The injection pattern refers to a pattern of time intervals for one (or each) injection when the urea water injection unit 36 ​​repeats injection intermittently. Figures 11(a) to 11(c) are explanatory diagrams for explaining the injection patterns of urea water.

[0057] The control unit C observes the transition of the exhaust temperature T over the elapsed time t as shown in FIG. 11(a), calculates the change rate α of the exhaust temperature T by the formula (1) as shown in FIG. 11(b), and determines the injection pattern of the urea water each time based on the calculated change rate α as shown in FIG. 11(c). For example, the larger the change rate α, the shorter the time interval for the injection of the urea water is set, and the smaller the change rate α, the longer the time interval for the injection of the urea water is set. This makes it possible to optimize the time interval for the injection of the urea water and suppress unnecessary injection of the urea water. As a result, it is possible to prevent the occurrence of problems such as clogging of the urea water injection nozzle 36a.

[0058] Returning to FIG. 9, the control unit C controls the urea water injection unit 36 ​​to continue injecting the urea water until the exhaust temperature falls below the first set value (step #3). When the exhaust temperature falls below the first set value (Y in step #3), the control unit C acquires detection information from the SCR catalyst temperature sensor S3 and determines whether the detection value of the SCR catalyst temperature falls below the second set value. When the detection value is equal to or higher than the second set value, the control unit C returns to step #2 and controls the urea water injection unit 36 ​​to continue injecting the urea water (N in step #4). Here, the second set value is set to a temperature at which the SCR catalyst 42 is in an activated state, and is, for example, 300 degrees. With this configuration, when the SCR catalyst 42 is in an activated state, the injection of the urea water by the urea water injection unit 36 ​​continues. Therefore, even if the exhaust temperature temporarily drops due to, for example, intermittent depression of the accelerator pedal, the injection of the urea water can be continued to reduce the emission of NOx.

[0059] On the other hand, if it is determined that the detected value of the SCR catalyst temperature is lower than the second set value, the urea water injection unit 36 ​​is controlled to stop the injection of the urea water (step #5). Then, the process returns to step #1, and the detected value of the exhaust gas temperature is monitored.

[0060] The embodiment of the present invention has been described above. The present invention is not limited to the above embodiment. It goes without saying that the present invention can be modified appropriately within the scope of the technical concept.

[0061] <6. Control of urea water injection unit in another embodiment> FIG. 12 is a flowchart relating to control of a urea water injection unit in another embodiment. In another embodiment, the urea water injection unit 36 ​​is controlled as shown in Fig. 12 by calculating the time from the start of the engine E and the time from the operation of the work machine, and by referring to these two times during manual regeneration of the DPF device 30, if it is determined that a long time has passed since the start of the work and that the work will end soon, or that the work machine is stopped and the engine will be stopped immediately after the end of regeneration, the urea water is injected more than usual during the DPF cooling process after the end of post-injection during regeneration, thereby lowering the exhaust temperature and lowering the temperature of the muffler downstream of the DPF. This allows the cooling to be accelerated by injecting a large amount of urea water and lowering the exhaust temperature, thereby suppressing heat damage after the engine E is stopped.

[0062] <7. Control of urea water injection unit in another embodiment (2)> Fig. 13 is a flow chart relating to the control of the urea water injection unit in another embodiment (2). As shown in Fig. 13, the urea instruction injection amount of the exhaust gas purification device M and the amount of urea water remaining in the urea water tank 36c are monitored, and if the actual amount remaining in the tank is greater than the amount predicted from the cumulative injection amount, it is determined that the SCR injector (urea water injection nozzle 36a) is clogged, and an error is issued to a predetermined display unit such as a monitor. Furthermore, the injection amount and injection pressure of the urea water injection nozzle 36a may be increased to blow away clogging such as dirt.

[0063] <8. Arrangement of the urea water tank in the alternative embodiment (3)> FIG. 14 is a schematic diagram showing the layout of a urea water tank according to another embodiment (3). 14, the urea water tank 36c may be disposed so as to be surrounded by the fuel tanks Et. Furthermore, the fuel tanks Et are connected by connecting pipes, and the fuel supply circuit to the engine E and the return circuit are connected to another fuel tank Et. In this way, by surrounding the urea water tank 36c with the fuel tanks Et, the influence of the outside air temperature can be suppressed, and by combining multiple fuel tanks Et to surround the urea water tank 36c, the upper surface of the urea water tank 36c can be enclosed.

[0064] <9. Arrangement of the urea water tank in the alternative embodiment (4)> FIG. 15 is a schematic diagram showing the layout of a urea water tank according to another embodiment (4). 15, the urea water tank 36c may be configured to have a fuel pipe provided therein, to connect a fuel return circuit from the engine E via a switching valve, and to return the fuel discharged from the urea water tank 36c to the fuel tank Et. Thereby, although there is a risk of the urea water freezing in a low-temperature environment, by circulating the returned fuel from the engine E inside the urea water tank 36c, freezing of the urea water at low temperatures can be prevented early.

[0065] <10. Arrangement of the urea water tank in the alternative embodiment (5)> FIG. 16 is a schematic diagram showing the layout of a urea water tank according to another embodiment (5). 16, the urea water tank 36c may be configured such that a fuel pipe is provided therein, a fuel return circuit from the engine E is connected via a switching valve, and the switching valve is operated depending on the outside air temperature and the state of the urea water to return the fuel coming out of the urea water tank 36c to the fuel tank Et. Thereby, although there is a risk of the urea water freezing in a low-temperature environment, by circulating the returned fuel from the engine E in the urea water tank 36c, freezing of the urea water at low temperatures can be prevented early. At an outside air temperature at which the urea water does not freeze or after the freezing is removed, the switching valve is operated to prevent fuel from flowing into the urea water tank 36c, thereby preventing deterioration of the urea water due to high temperatures.

[0066] <Modification> FIG. 17 is a schematic diagram showing the configuration of a blower turbine 38 according to a modified example. 17, the blower turbine 38 may be configured to have a blade section 38a that blows air and a driven blade section 38b that is disposed in the urea mixing pipe 35 and rotates by the passage of exhaust gas, and the rotation of the driven blade section 38b is transmitted to the blade section 38a by a connecting shaft 38c. This makes it possible to increase the exhaust gas discharge amount and reduce the exhaust pressure by utilizing the movement of the exhaust gas inside the pipe.

[0067] Further variations are listed below. The urea mixing pipe 35 connecting the DPF device 30 and the SCR device 40 may be configured to have the same diameter without restricting the pipe. This can reduce exhaust pressure. The urea mixing pipe 35 is designed to branch into two systems (pipe division) at the beginning of the urea mixing pipe 35 and merge in the middle, and a urea water injection nozzle 36a is provided at the merged part, thereby promoting mixing.

[0068] In the above embodiment, in Figs. 11(a) to 11(c), the change rate α of the exhaust temperature T is calculated, and the injection pattern of the urea water is determined each time as shown in Fig. 11(c) based on the calculated change rate α. However, the control unit C may calculate the difference between the concentrations of the upstream and downstream NOx concentration sensors S5 based on the detection value of the NOx concentration sensor S5, and may determine the injection pattern of the urea water each time based on the change rate of the difference. For example, the larger the change rate of the difference, the shorter the time interval of the injection of the urea water is set, and the smaller the change rate of the difference, the longer the time interval of the injection of the urea water is set. This optimizes the time interval of the injection of the urea water, and prevents unnecessary injection of the urea water. As a result, the occurrence of problems such as clogging of the urea water injection nozzle 36a can also be prevented.

[0069] In the above embodiment, as shown in Figure 8, a configuration is shown in which the cabin side bracket 49a, soft rubber g1, support fixing base 48, hard rubber g2, and cabin side bracket 49a are arranged in this order from above. However, the support fixing base 48, soft rubber g1, cabin side bracket 49a, hard rubber g2, and cabin side bracket 49a can also be arranged in this order from above.

[0070] In the example shown in FIG. 6, an ammonia absorbent that absorbs ammonia may be further provided in the exhaust pipe 44. [Explanation of symbols]

[0071] 1 Work vehicle 1a Body 2 Front wheels 3 Rear wheel 4 Exhaust muffler 5. Gearbox 7 Coupling device 8. Cockpit 9 Cabin 10. Dashboard 11 Steering handle 20a Cylinder block 20b Cylinder head 20c Cylinder cover 23 Flywheel case 24a Suction part 24b Turbocharger 24c intake throttle 24d intake manifold 25 Injector 25a injector solenoid valve 26 Exhaust manifold 27 EGR device 27a EGR cooler 27b EGR pipe 27c EGR valve 28 Connecting Pipe 30 DPF device 31 DPF case 32 PM oxidation catalyst 33 Filters 35 Urea mixing pipe (mixing piping) 36 Urea water injection part 37 Water injection part 38 Blower Turbine 39 Mixer section 40 SCR device 41 SCR case 41a Swirl generating plate 42 SCR catalyst 43 Ammonia oxidation catalyst 44 Discharge pipe 45 Oxidizer injection section 46 Heating wire 47 Exhaust valve 48 Support fixed seat 49a Cabin side bracket 49b Body side bracket g1 Soft rubber g2 Hard rubber 50 ECU 60 DCU C control section E-Engine M Exhaust gas purification device

Claims

1. A work vehicle equipped with an exhaust gas purification device that processes and purifies exhaust gas discharged from an engine, The exhaust gas purification device includes, in order from the upstream side, a DPF device that removes particulate matter from exhaust gas, a urea mixing tube that injects urea water into the exhaust gas inside the tube and mixes it, and an SCR device that removes nitrogen oxides, The SCR device includes an SCR case connected to an end of the urea mixing tube, an SCR catalyst and an ammonia oxidation catalyst disposed in the SCR case, and an exhaust pipe connected to an outlet portion of the SCR case, The exhaust pipe is provided with an ammonia emission suppression means for suppressing the emission of ammonia, The work vehicle is characterized in that the ammonia emission suppression means includes an electric heating wire that heats the inside of the exhaust pipe, and an exhaust valve that increases the exhaust pressure of the exhaust pipe.

2. 2. The work vehicle according to claim 1, wherein a swirl generating plate having a flat plate formed in a spiral shape is provided on an inner wall of the SCR case.

3. 2. The work vehicle according to claim 1, wherein the SCR case is disposed vertically with its longitudinal direction extending up and down.

4. 4. The work vehicle according to claim 3, further comprising an oxidizer injection unit that injects an oxidizer into the exhaust pipe, as the ammonia emission suppression means.

5. a support and fixing base that supports and fixes a bottom portion of the SCR case; The work vehicle according to claim 3, characterized in that the support fixing seat is cantilevered between a cabin side bracket fixed to a cabin of the work vehicle and a vehicle body side bracket fixed to the vehicle body with an elastic body interposed therebetween.

6. a urea water injection unit disposed in the urea mixing tube and configured to inject urea water; A control unit that controls the injection of the urea injection unit; an exhaust gas temperature sensor for detecting the temperature of exhaust gas discharged from the engine; an SCR catalyst temperature detection sensor for detecting a temperature of the SCR catalyst; The control unit acquires detection information from the exhaust temperature sensor and the SCR catalyst temperature detection sensor, and controls the urea injection unit to perform injection when the detection value of the exhaust temperature sensor becomes equal to or greater than a first set value; and 6. The work vehicle according to claim 1, wherein the urea injection unit is controlled to stop injection when a detection value of the exhaust gas temperature sensor falls below the first set value and a detection value of the SCR catalyst temperature detection sensor falls below a second set value.

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