Work vehicles

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 for purifying exhaust gas.

Background Art

[0002] Conventionally, in order to process and purify exhaust gas discharged from an engine, a work vehicle equipped with an exhaust gas purification device is known (for example, see Patent Document 1 below). This exhaust gas purification device includes a DPF (Diesel particulate filter) device for removing particulate matter from exhaust gas and a SCR (Selective Catalytic Reduction) device for removing NOx.

[0003] Here, the SCR device includes an aqueous urea injection unit that injects aqueous urea and a SCR catalyst. The aqueous urea injection unit injects aqueous urea into a path through which exhaust gas passes. Urea contained in the aqueous urea is hydrolyzed into ammonia by contacting the high-temperature exhaust gas. The SCR catalyst is composed of materials such as zeolite and ceramic that adsorb ammonia. NOx (nitrogen oxides) contained in the exhaust gas is reduced by contacting the SCR catalyst that has adsorbed ammonia and is changed into nitrogen and water. Thus, it is a mechanism for suppressing the emission amount of NOx.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] However, SCR systems can release excess ammonia that is not used for reduction into the outside air, which can lead to ammonia slip. In some cases, an oxidation catalyst is placed downstream of the SCR catalyst to treat this residual ammonia, but if the amount of residual ammonia is large, the treatment may be insufficient. Therefore, the present invention aims to solve these problems and provide a work vehicle that can smoothly treat residual ammonia in an SCR system and effectively prevent ammonia slip. [Means for solving the problem]

[0006] To achieve the above objective, the first invention is: A work vehicle equipped with an exhaust gas purification device that processes and purifies exhaust gases emitted from the engine, The exhaust gas purification device comprises, in order from the upstream side, a DPF device for removing particulate matter from exhaust gas, a urea mixing pipe for injecting and mixing urea water with exhaust gas within the pipe, and an SCR device for removing nitrogen oxides. The SCR apparatus comprises an SCR case connected to the end of the urea mixing pipe, an SCR catalyst and an ammonia oxidation catalyst disposed within the SCR case, and a discharge pipe connected to the outlet portion of the SCR case. The discharge pipe is equipped with an ammonia discharge suppression means for suppressing the discharge of ammonia, The present invention provides a work vehicle characterized by comprising, as a means for suppressing ammonia emissions, an electric heating wire for heating the inside of the discharge pipe and a discharge valve for increasing the exhaust pressure of the discharge pipe.

[0007] According to the first invention described above, by heating the inside of the pipe, residual ammonia can be evaporated, preventing ammonia slippage, while the discharge of ammonia can be suppressed by a discharge valve that increases the exhaust pressure.

[0008] The second invention, in addition to the configuration of the first invention, The SCR case is characterized in that a swirl generating plate, which is a flat plate formed in a spiral shape, is provided on its inner wall.

[0009] According to the second invention described above, in addition to the effects of the first invention described above, the swirl generating plate generates a swirl (a vortex formed by the working fluid), and by obtaining a stirring effect, the reaction of the urea solution is enhanced and ammonia slip can be more effectively prevented.

[0010] The third invention, in addition to the configuration of the first invention, The SCR case is characterized by having a vertical orientation with its length in the vertical direction.

[0011] According to the third invention described above, in addition to the effects of the first invention, by arranging the SCR case in a vertical configuration with the vertical direction as its length, residual ammonia is made less likely to be discharged by allowing it to flow down, thereby further improving the prevention of ammonia slip.

[0012] The fourth invention, in addition to the configuration of the third invention described above, As a means for suppressing ammonia emissions, the invention is further characterized by the provision of an oxidizing agent injection unit that injects an oxidizing agent into the pipe of the discharge pipe.

[0013] According to the fourth invention described above, in addition to the effects of the third invention described above, the oxidizing agent injection unit can oxidize residual ammonia in the pipe, thereby preventing ammonia slip. Furthermore, because the SCR case is arranged vertically, a portion of the oxidizing agent injected by the oxidizing agent injection unit is supplied to the ammonia oxidation catalyst in the SCR case, thereby further promoting the oxidation of ammonia and enabling better prevention of ammonia slip.

[0014] The fifth invention, in addition to the configuration of the third invention described above, The SCR case is provided with a support and fixing seat that supports and secures the bottom of the case. The support and fixing seat is characterized in that it is cantilevered and clamped 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 between them.

[0015] According to the fifth invention described above, in addition to the effects of the third invention, since the SCR case is arranged vertically, the upper part of the SCR device is likely to vibrate. Therefore, by adopting a configuration in which a support and fixing seat for supporting and fixing the bottom of the SCR case is cantilevered and clamped with an elastic body interposed therebetween, wear failures and the like caused by 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 characterized in that, in addition to the configuration of any one of the first to fifth inventions described above, a urea water injection part that is arranged in the urea mixing pipe and injects urea water; a control part that controls the injection of the urea injection part; an exhaust temperature sensor that detects the temperature of exhaust gas discharged from the engine; and an SCR catalyst temperature detection sensor that detects the temperature of the SCR catalyst, wherein the control part acquires the detection information of the exhaust temperature sensor and the SCR catalyst temperature detection sensor, and controls the urea injection part to perform injection on the condition that the detection value of the exhaust temperature sensor is equal to or higher than a first set value. Also, the control part controls the urea injection part to stop injection on the condition that the detection value of the exhaust temperature sensor is lower than the first set value and the detection value of the SCR catalyst temperature detection sensor is lower than a second set value.

[0017] According to the sixth invention described above, in addition to the effects of any one of the first to fifth inventions described above, when the SCR catalyst is in an activated state, the injection of urea water by the urea water injection part is continued. Therefore, for example, even when the exhaust temperature temporarily drops due to an intermittent pressing operation of the accelerator pedal by an operator, the injection of urea water can be continued to reduce the emission of nitrogen oxides.

Advantages of the Invention

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

Brief Description of the Drawings

[0019] [Figure 1] Figure 1 is a left side view of a work vehicle according to a preferred embodiment of the present invention. [Figure 2] Figure 2 is a plan view of the same. [Figure 3] Figure 3 is a perspective view showing the configuration around the engine as viewed from the left rear side, [Figure 4] Figure 4 is a front view showing the configuration of the engine and the exhaust gas purification device. [Figure 5] Figure 5 is a right side view showing the configuration around the engine. [Figure 6] Figure 6 is an explanatory diagram schematically showing the intake and exhaust flows of the configuration around the engine. [Figure 7] Figure 7 is a schematic main part front view showing the arrangement configuration of the SCR case. [Figure 8] Figure 8 is a block diagram showing the configuration of a control unit that controls each mechanism of the work vehicle. [Figure 9] Figure 9 is a flowchart related to the control of the urea water injection unit. [Figure 10] Figure 10 is a diagram showing a urea water injection amount map for determining the urea water injection amount. [Figure 11] Figures 11(a) to 11(c) are explanatory diagrams for explaining the injection pattern of urea water. [Figure 12] Figure 12 is a flowchart related to the control of the urea water injection unit in another embodiment. [Figure 13] Figure 13 is a flowchart related to the control of the urea water injection unit in another embodiment (2). [Figure 14] Figure 14 is a schematic configuration diagram showing the arrangement configuration of the urea water tank in another embodiment (3). [Figure 15] Figure 15 is a schematic configuration diagram showing the arrangement configuration of the urea water tank in another embodiment (4). [Figure 16] Figure 16 is a schematic configuration diagram showing the arrangement configuration of the urea water tank in another embodiment (5). [Figure 17]Figure 17 is a schematic diagram showing the configuration of a modified blower turbine. [Modes for carrying out the invention]

[0020] <1. Overall composition of work vehicles> Preferred embodiments of the present invention will be described in detail below with reference to the attached drawings. Figure 1 is a left side view of a work vehicle according to a preferred embodiment of the present invention, and Figure 2 is a top view. A preferred embodiment of the present invention, the work vehicle 1, 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 running body 1a that forms the frame of the machine, front wheels 2, rear wheels 3, an engine E as a power source, and a transmission 5. Of these, the front wheels 2 are mainly used for steering, i.e., as steering wheels. The rear wheels 3 are mainly used for driving, i.e., as drive wheels. The rotational power generated by the engine E, which is mounted in the bonnet 6 at the front of the machine, is transmitted to the rear wheels 3 after being appropriately reduced by the transmission in the transmission case 5, and the rear wheels 3 generate driving force from this rotational power. In addition, an exhaust gas purification device M is installed near the engine E to process the exhaust gas discharged from the engine.

[0022] The transmission 5 can transmit the rotational power generated by the engine E to the front wheels 2 as needed. In this case, all four wheels, including the front wheels 2 and the rear wheels 3, become drive wheels and generate driving force. In other words, the transmission 5 can switch between two-wheel drive and four-wheel drive, reducing the rotational power of the engine E and transmitting the reduced rotational power to the front wheels 2 and the rear wheels 3. The tractor 1 is also equipped with a coupling device 7 at the rear of the machine body, to which implements such as a rotary tiller (not shown) can be attached. The coupling device 7 is, for example, a three-point link consisting of a top link 7a at the top center and lower links 7b, 7b on the left and right at the bottom, and connects the implement to the rear of the tractor 1. As described later, the tractor 1 can raise and lower the implement via the lift rod and the lower links 7b connected to the lift rod by rotating the left and right lift arms hydraulically.

[0023] The cockpit 8 on the aircraft is surrounded by a cabin 9. This cabin 9 is located on top of the vehicle body 1a, and inside the cabin 9, a steering wheel 11 is erected from the dashboard 10 in front of the cockpit 8, and various control pedals such as a clutch pedal, brake pedal, and accelerator pedal, as well as various control levers such as a forward / reverse lever and a gear shift lever are arranged around the cockpit 8.

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

[0025] <2. Engine Configuration> Next, we will explain the configuration of the engine area (engine E and exhaust gas purification device M). Figure 3 is a perspective view showing the configuration around the engine as seen from the left rear, Figure 4 is a front view showing the configuration around the engine, Figure 5 is a right side view showing the configuration around the engine, and Figure 6 is an explanatory diagram schematically showing the intake and exhaust airflow of the configuration around the engine.

[0026] Engine E is, for example, a diesel engine. As shown in Figures 3 to 5, the external configuration of this engine E is such that a cylinder head 20b and cylinder cover 20c are provided on the upper part of the cylinder block 20a, and an oil pan 21 is provided on the lower part of the cylinder block 20a. In addition, the engine E is provided with a cooling fan rotation mechanism 22 for rotating a cooling fan (not shown) at the front of the cylinder block 20a, and a flywheel case 23 with a flywheel (not shown) connected to the crankshaft is provided at the lower rear of the cylinder block 20a. The cylinder block 20a contains multiple cylinders arranged so that multiple pistons connected to the crankshaft reciprocate.

[0027] As shown in Figure 6, the internal configuration of engine E includes an intake section 24a, a supercharger 24b, an intake throttle (intake throttling device) 24c, and an intake manifold 24d as components of the intake system. The gas drawn in from 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 in the diagram) is located below the intake manifold 24d. The common rail stores fuel at high pressure and supplies it to the injector 25 (fuel injection device) located in the cylinder head 20b.

[0029] The injector 25 is equipped with an injector solenoid valve 25a (see Figure 8). The injector solenoid valve 25a injects fuel into the combustion chamber by opening and closing at timings in accordance with instructions from the ECU 50.

[0030] Although not shown in Figures 3 to 6, engine E is equipped with an engine speed sensor S1 that detects engine speed (rotational speed r / min, number of crankshaft rotations per predetermined time) and an engine output sensor S2 that detects engine output Le (kW) (see Figure 8). The engine speed sensor S1 and engine output sensor S2 output the detected engine speed and engine output to the ECU 50.

[0031] Engine E is also equipped with an exhaust manifold 26. A portion of the gas that passes through the exhaust manifold 26 is supplied to the EGR device 27, while the remainder is supplied to the exhaust gas purification device M. The EGR device 27 comprises an EGR cooler 27a, an EGR pipe 27b, and an EGR valve 27c. The valve opening of the EGR valve 27c is controlled by the ECU 50.

[0032] <2. Configuration of the exhaust gas purification system (DPF system)> Next, the exhaust gas purification device M will be described with reference to Figure 6. The exhaust gas discharged through the exhaust manifold 26 of the engine 3 is taken in through the exhaust connection pipe 28 via the exhaust turbine section 24e of the supercharger 24b. The exhaust gas that has been purified by the exhaust gas purification device M is discharged outside the machine through the exhaust muffler 4 (see Figure 1).

[0033] The exhaust gas purification system M comprises a DPF device 30 and an SCR device 40, arranged in order from the upstream side of the exhaust gas. Note that some of the devices and components of the DPF device 30 and SCR device 40 shown in Figure 6 are omitted from Figures 3 to 5.

[0034] The DPF device 30 performs the function of capturing and removing particulate matter (PM) contained in the exhaust gas. The DPF device 30 comprises a DPF case 31, a PM oxidation catalyst 32, and a filter 33.

[0035] The DPF case 31 is a roughly cylindrical, hollow component, and a PM oxidation catalyst 32 and a filter 33 are arranged inside. The PM oxidation catalyst 32 is made of platinum or the like and is a catalyst for oxidizing (burning) unburned fuel, carbon monoxide, nitric oxide, etc. contained in the exhaust gas. The filter 33 is configured, for example, as 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 pipe). 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, a blower turbine 38 that reduces exhaust pressure, and a mixer unit 39 that agitates the airflow inside the pipe.

[0037] The urea water injection unit 36 ​​comprises 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 drives the urea water stored in the urea water tank 36c to be injected from the urea water injection nozzle 36a. By injecting urea water into the urea mixing tube 45, urea hydrolyzes and ammonia is generated. The presence or absence of urea water injection and the amount of injection of urea water in the urea water injection unit 36 ​​are controlled by a DCU (Dosing Control Unit) 60. The DCU 95, for example, starts injecting urea water when the exhaust gas temperature exceeds the temperature at which urea hydrolyzes into ammonia.

[0038] The water injection unit 37 comprises a water injection nozzle 37a, a water pump 37b, and a water tank 37c. The water pump 36b drives the water stored in the water tank 36c to be injected from the water injection nozzle 36a. The water injection nozzle 37a is positioned opposite the tip of the urea water injection nozzle 36a and sprays water towards the urea water injection nozzle 36a. Since the tip of the urea water injection nozzle 36a becomes unable to spray if the urea water crystallizes, crystallization can be prevented by periodically spraying water with the water injection unit 37 at predetermined time intervals. The water injection nozzle 37a is positioned with an incline (approximately 45° with respect to the longitudinal direction of the piping), which allows for good spraying towards the tip of the urea water injection nozzle 36a. Furthermore, by shifting the front-to-back positioning of the urea water injection nozzle 36a and the water injection nozzle 37a, it is prevented that the urea water adheres to the water injection nozzle 37a and crystallizes. Furthermore, the presence or absence of water injection and the amount of water injected by the DCU 60 are controlled by the water injection unit 37.

[0039] The blower turbine 38 is located inside the urea mixing tube 35 and is a blower that uses an electric motor to rotate turbine-shaped blades to blow air. By driving this blower turbine 38, it reduces exhaust pressure and promotes exhaust from the DPF device 30.

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

[0041] <3. Configuration of the exhaust gas purification system (SCR system)> The SCR device 40 receives exhaust gas from the urea mixing pipe 35 and performs the function of removing NOx contained in the exhaust gas. The SCR device 40 comprises 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 roughly cylindrical, hollow member, and contains the SCR catalyst 42 and ammonia inside. A near-oxidation catalyst 43 is installed. The SCR catalyst 42 is made of materials such as zeolite and ceramic that adsorb ammonia. The ammonia generated when the urea water injection unit 36 ​​injects urea water is adsorbed by the SCR catalyst 42. NOx contained in the exhaust gas is reduced when it comes into contact with the SCR catalyst 42 that has adsorbed ammonia, and is changed into nitrogen and water.

[0043] Here, the SCR case 41 is arranged vertically with its length in the vertical direction, which allows residual ammonia to flow down and is less likely to be discharged, thereby effectively preventing ammonia slip. Furthermore, a swirl generating plate 41a, which is a flat plate formed in a spiral shape, is provided on the inner wall of the SCR case 41, in front of (upstream of) the SCR catalyst 42, extending from the inner wall. This swirl generating plate 41a generates a swirl (a vortex formed by the working fluid), and by obtaining a stirring effect, the reaction of the urea solution is enhanced, further effectively preventing ammonia slip.

[0044] The ammonia oxidation catalyst 43 is a catalyst that prevents ammonia that has been detached from the SCR catalyst 42 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, converting 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] Furthermore, an SCR catalyst temperature sensor S3 is installed near the SCR catalyst 42. The SCR catalyst temperature sensor S3 detects the temperature of the SCR catalyst 42 and outputs the result to the DCU 60.

[0046] Furthermore, in order to detect NOx concentrations upstream and downstream, NOx concentration sensors S5 are installed at the inlet portion of the DPF case 31 and the outlet portion of the SCR case 41, respectively. The NOx concentration detected by these NOx sensors S5 can be used primarily to determine the injection interval of urea solution. In addition, 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 installation location of the exhaust temperature sensor S4 is not limited to the illustrated example and may be installed at an appropriate location where the temperature of the exhaust gas discharged from the engine E can be detected.

[0047] The exhaust pipe 44 is connected at its starting end to the outlet portion of the SCR case 41 and at its end to the exhaust muffler 4, and serves the function of sending 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 element 46, and an exhaust valve 47, in that order from the upstream side of the exhaust gas.

[0048] The oxidant injection unit 45 comprises an oxidant injection nozzle 45a for injecting the oxidant, an oxidant pump 45b, and an oxidant tank 45c. The oxidant pump 45 drives the oxidant stored in the oxidant tank 45c to be injected from the oxidant injection nozzle 45a. This oxidizes the residual ammonia in the pipe, preventing ammonia slip. Furthermore, because the SCR case 61 is arranged vertically, a portion of the oxidant injected by the oxidant injection nozzle 45a is supplied to the ammonia oxidation catalyst 43, thereby promoting the oxidation of ammonia and providing better prevention of ammonia slip.

[0049] The heating element 46 is installed on the inner wall of the exhaust pipe 44 and heats the inside of the pipe, thereby evaporating residual ammonia and preventing ammonia slippage. This allows for the smooth processing of residual ammonia in the SCR device 40. 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 higher the exhaust pressure inside the pipe (and the SCR device 40) can be, thereby suppressing the discharge of ammonia.

[0050] Figure 7 is a schematic front view of the main components showing the arrangement of the SCR case 41. As shown in Figure 7, the support and fixing seat 48 that supports and fixes the bottom of the SCR case 41 is cantilevered between 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 material) is interposed between the cabin-side bracket 49a and the support and fixing seat 48, and a hard rubber g2 (hard elastic material) is interposed between the vehicle-side bracket 49b and the support and fixing seat 48. This configuration improves the cushioning effect with the soft rubber g1 and prevents wear failures with the hard rubber g2. Furthermore, as shown in the figure, it is preferable that the end portion of the urea mixing pipe 35 be made of flexible piping to prevent vibrations from being transmitted from the engine E to the SCR device 40. With the above configuration, vibrations of the SCR device 40 can be effectively prevented. In particular, because the upper part of the SCR device 40 is prone to vibration due to the vertical arrangement of the SCR case 41, the above configuration can effectively prevent wear failures and the like due to vibration.

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

[0052] As shown in Figure 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. The output side of the control unit C is connected to an actuator group including an injector solenoid valve 25a, an EGR valve 27a, an intake throttle 24c, an exhaust valve 47, a blower turbine 38, and a mixer unit 39, which are connected to the ECU 50. The urea water injection unit 36, a water injection unit 37, and an oxidizer injection unit 45 are connected to the DCU 60.

[0053] <5. Control of the urea water injection unit> Next, referring to Figures 9 to 11, the control unit C will be used to explain the control of the urea water injection unit. Figure 9 is a flowchart related to the control of the urea solution injection unit. Figure 10 is a diagram showing the urea solution injection amount map that determines the amount of urea solution injected. Figure 11 is an explanatory diagram illustrating the urea solution injection interval.

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

[0055] As shown in Figure 10, the injection amount is determined by the detected values ​​of engine speed (r / min) and engine output (kW). That is, the urea solution injection amount map is a map in which the vertical axis is engine output (kW) and the horizontal axis is engine speed (r / min), and the set value of the injection amount is stored for each point on the map, as shown in the figure. A point on the urea solution injection amount map is determined by the detected values ​​of engine speed (r / min) and engine output (kW), and the injection amount is determined so that it matches the set value of that point. Also, as shown in the figure, the set value of the injection amount on the urea solution injection amount map is configured so that the injection amount increases proportionally as the engine output increases, but within the same engine output range, the injection amount increases gradually as the engine speed increases. The numerical value of the injection amount shown in the figure indicates, for example, the amount injected in one (or one) injection from the urea solution injection unit 36.

[0056] Furthermore, the control unit C determines the urea solution injection pattern and performs the urea solution injection. The injection pattern refers to the pattern of the time interval between each injection (or single injection) when the urea solution injection unit 36 ​​intermittently repeats injections. Figures 11(a) to 11(c) are explanatory diagrams illustrating the urea solution injection pattern.

[0057] As shown in Figure 11(a), the control unit C observes the change in exhaust temperature T over elapsed time t, and as shown in Figure 11(b), calculates the rate of change α of exhaust temperature T using equation (1). Based on this calculated rate of change α, the control unit C determines the urea solution injection pattern each time, as shown in Figure 11(c). For example, the larger the rate of change α, the shorter the time interval for urea solution injection is set, and the smaller the rate of change α, the longer the time interval for urea solution injection is set. This optimizes the time interval for urea solution injection and suppresses unnecessary urea solution injection. As a result, problems such as clogging of the urea solution injection nozzle 36a can also be prevented.

[0058] Returning to Figure 9, the control unit C controls the urea water injection unit 36 ​​to continue injecting urea water until the exhaust temperature falls below a 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 detected value of the SCR catalyst temperature falls below a second set value. If it is above the second set value, the control unit returns to step #2 and controls the urea water injection unit 36 ​​to continue injecting urea water (N in step #4). Here, the second set value is the temperature at which the SCR catalyst 42 becomes activated, for example, 300 degrees. With this configuration, when the SCR catalyst 42 is activated, the injection of urea water by the urea water injection unit 36 ​​continues. Therefore, even if the exhaust temperature temporarily drops due to, for example, intermittent pressure on the accelerator pedal, the injection of urea water can be continued to reduce NOx emissions.

[0059] On the other hand, if the detected SCR catalyst temperature is determined to be below the second set value, the urea solution injection unit 36 ​​is controlled to stop the injection of urea solution (step #5). Subsequently, the process returns to step #1, and the detected exhaust temperature is monitored.

[0060] The embodiments of the present invention have been described above. The present invention is not limited to the embodiments described above. It goes without saying that modifications can be made as appropriate within the scope of the technical idea.

[0061] <6. Control of the urea water injection unit in another embodiment> Figure 12 is a flowchart relating to the control of the urea solution injection unit in another embodiment. In the control of the urea water injection unit 36 ​​in another embodiment, as shown in Figure 12, the time since the engine E started and the time since the work machine started operating are calculated, and when the DPF device 30 is manually regenerated, these two times are referenced, and if a long time has passed since the start of work and it is thought that the work will be finished soon, or if the work machine has stopped and it is thought that the engine will be stopped immediately after the regeneration is finished, then during the DPF cooling stroke after the post-injection is completed in the regeneration process, more urea water than usual is injected to lower the exhaust temperature and thereby lower the temperature of the muffler downstream of the DPF. As a result, cooling can be accelerated by injecting more urea water to lower the exhaust temperature and suppress heat damage after the engine E is stopped.

[0062] <7. Control of the urea water injection unit in another embodiment (2)> Figure 13 is a flowchart relating to the control of the urea water injection unit in another embodiment (2). As shown in Figure 13, the urea indicative injection amount of the exhaust gas purification device M and the remaining amount of urea water in the urea water tank 36c are monitored, and if the actual remaining amount in the tank is greater than the amount predicted from the cumulative injection amount, it is determined that a blockage has occurred in the SCR injector (urea water injection nozzle 36a), and the system is controlled to issue an error alert 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 any blockages such as debris.

[0063] <8. Arrangement configuration of the urea water tank in another embodiment (3)> Figure 14 is a schematic diagram showing the arrangement of a urea water tank in another embodiment (3). As shown in Figure 14, the urea water tank 36c may be arranged so as to be surrounded by each fuel tank Et. Furthermore, each fuel tank Et is connected by connecting pipes, and the fuel supply circuit and return circuit to the engine E are connected to another fuel tank Et. In this way, the influence of ambient temperature can be suppressed by surrounding the urea water tank 36c with fuel tanks Et, and by combining multiple fuel tanks Et to surround the urea water tank 36c, the urea water tank 36c can be surrounded up to its top surface.

[0064] <9. Arrangement configuration of the urea water tank in another embodiment (4)> Figure 15 is a schematic diagram showing the arrangement of a urea water tank in another embodiment (4). As shown in Figure 15, the urea water tank 36c may be configured to have fuel piping inside the tank and a fuel return circuit from the engine E connected via a switching valve, so that the fuel coming out of the urea water tank 36c is returned to the fuel tank Et. This prevents the urea water from freezing in low-temperature environments by circulating the return fuel from the engine E within the urea water tank 36c, thus quickly eliminating urea water freezing at low temperatures.

[0065] <10. Arrangement configuration of urea water tank in another embodiment (5)> Figure 16 is a schematic diagram showing the arrangement of a urea water tank in another embodiment (5). As shown in Figure 16, the urea water tank 36c may be configured to have a fuel pipe inside the tank, a fuel return circuit from the engine E connected via a switching valve, and to activate the switching valve depending on the ambient temperature and the state of the urea water, returning the fuel coming out of the urea water tank 36c to the fuel tank Et. This prevents the urea water from freezing in low-temperature environments, as circulating the return fuel from the engine E within the urea water tank 36c can quickly resolve the freezing of the urea water at low temperatures. When the ambient temperature is such that the urea water does not freeze, or after the freezing has been resolved, the switching valve can be activated to prevent fuel from flowing into the urea water tank 36c, thereby preventing deterioration of the urea water due to high temperatures.

[0066] <Variation> Figure 17 is a schematic diagram showing the configuration of a modified blower turbine 38. As shown in Figure 17, the blower turbine 38 may be configured to include a blade section 38a that blows air and a driven blade section 38b disposed within the urea mixing pipe 35 and rotating due to the passage of exhaust gas, with the rotation of the driven blade section 38b being transmitted to the blade section 38a by a connecting shaft 38c. This makes it possible to increase the amount of exhaust gas discharged and reduce the exhaust pressure by utilizing the movement of the exhaust gas within 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 no restriction and be connected with the same diameter. This can reduce the exhaust pressure. Mixing can be promoted by designing the urea mixing pipe 35 to branch into two systems (pipe division) at its starting end and merge them in the middle, and by arranging a urea water injection nozzle 36a at the merging point.

[0068] In the above embodiment, Figures 11(a) to 11(c) show an example in which the rate of change α of the exhaust temperature T is calculated, and the urea water injection pattern is determined each time based on this calculated rate of change α, as shown in Figure 11(c). However, the control unit C may calculate the difference in concentration between the upstream and downstream NOx concentration sensors S5 based on the detected value of the NOx concentration sensor S5, and determine the urea water injection pattern each time based on the rate of change of this difference. For example, the larger the rate of change of the difference, the shorter the time interval for urea water injection is set, and the smaller the rate of change of the difference, the longer the time interval for urea water injection is set. This optimizes the time interval for urea water injection and suppresses unnecessary urea water injection. As a result, 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, the components are arranged in the following order from top to bottom: cabin-side bracket 49a, soft rubber g1, support fixing seat 48, hard rubber g2, and cabin-side bracket 49a. However, they can also be arranged in the following order from top to bottom: support fixing seat 48, soft rubber g1, cabin-side bracket 49a, hard rubber g2, and cabin-side bracket 49a.

[0070] In the illustrated example in Figure 6, an ammonia absorbent material for absorbing ammonia may be further provided inside the discharge pipe 44. [Explanation of Symbols]

[0071] 1. Work vehicles 1a Vehicle body 2 Front wheels 3 Rear wheels 4. Exhaust muffler 5. Transmission 7 Coupling device 8. Cockpit 9 cabins 10 Dashboard 11 Steering wheel 20a Cylinder Block 20b Cylinder head 20c Cylinder Cover 23 Flywheel Case 24a Suction part 24b Supercharger 24c intake throttle 24d Intake Manifold 25 Injectors 25a Injector Solenoid Valve 26 Exhaust Manifold 27 EGR device 27a EGR cooler 27b EGR pipe 27c EGR valve 28 connecting pipes 30 DPF devices 31 DPF cases 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 cases 41a Swirl generating plate 42 SCR catalyst 43 Ammonia oxidation catalyst 44 Discharge pipe 45 Oxidizing agent spray unit 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 gases emitted from the engine, The exhaust gas purification device comprises, in order from the upstream side, a DPF device for removing particulate matter from exhaust gas, a urea mixing pipe for injecting and mixing urea water with exhaust gas within the pipe, and an SCR device for removing nitrogen oxides. The SCR device comprises an SCR case connected to the end of the urea mixing pipe, an SCR catalyst and an ammonia oxidation catalyst disposed within the SCR case, and a discharge pipe connected to the outlet portion of the SCR case. The discharge pipe is equipped with an ammonia discharge suppression means for suppressing the discharge of ammonia, A work vehicle characterized in that, as the means for suppressing ammonia emission, it comprises an electric heating wire for heating the inside of the discharge pipe and an exhaust valve for increasing the exhaust pressure of the discharge pipe, wherein the electric heating wire heats and volatilizes the residual ammonia in the discharge pipe, and the exhaust valve is controlled to the closed position to increase the exhaust pressure in the discharge pipe, thereby suppressing the outflow of residual ammonia to the outside.

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

3. The work vehicle according to claim 1, characterized in that the SCR case is arranged vertically with its length in the vertical direction.

4. The work vehicle according to claim 3, further characterized in that an oxidizing agent injection unit is provided for injecting an oxidizing agent into the pipe of the discharge pipe as a means for suppressing ammonia emissions.

5. The SCR case is provided with a support and fixing seat that supports and fixes the bottom of the case, The work vehicle according to claim 3, characterized in that the support and fixing seat 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 between them.

6. The urea mixing tube is equipped with a urea water injection unit that sprays urea water, A control unit that controls the injection of the urea solution injection unit, An exhaust temperature sensor that detects the temperature of the exhaust gas emitted from the engine, The system includes an SCR catalyst temperature detection sensor for detecting the 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 water injection unit to perform injection when the detected value of the exhaust temperature sensor becomes equal to or greater than a first set value, and also, A work vehicle according to any one of claims 1 to 5, characterized in that the injection of urea water from the injection unit is stopped when the detected value of the exhaust temperature sensor falls below the first set value and the detected value of the SCR catalyst temperature detection sensor falls below the second set value.

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