JP6615724B2 - Exhaust treatment equipment - Google Patents

Description

  The present invention relates to control of an exhaust treatment device that purifies exhaust gas discharged from an engine when the engine is stopped.

  Conventionally, urea water is injected using an injection valve provided upstream of an SCR (Selective Catalyst Reduction) catalyst in an exhaust pipe in order to reduce nitrogen oxide (NOx) in exhaust gas exhausted by an engine such as a diesel engine. A technique for reducing nitrogen oxide in exhaust gas is known. Such urea water may freeze when it falls below -11 ° C. If the urea water freezes, the piping will be clogged, which will hinder the injection of urea water at the next engine start. Moreover, since urea water has the characteristic of degrading at high temperatures, deterioration may be accelerated if the urea water is maintained in a high temperature state when the engine is stopped after a high load operation.

  For example, Japanese Patent Application Laid-Open No. 2010-255608 (Patent Document 1) addresses such a problem by causing the pump for supplying urea water to the injection valve after the engine is stopped to move in the reverse direction and remain in the pipe. A technique for returning urea water to the tank is disclosed.

JP 2010-255608 A

  By the way, a plurality of injection valves for injecting urea water may be provided. For example, when the engine is a V-type engine, two exhaust pipes are connected to the engine in parallel. Therefore, it is necessary to provide two injection valves in order to inject urea water into each of the two exhaust pipes. In the case where a plurality of injection valves are provided, the cost, weight, and the like increase if piping, pumps, or tanks are individually provided. Therefore, it is conceivable to make a part of the piping, the pump and the tank have a common configuration by branching the piping halfway and connecting it to each injection valve.

  However, in the path from the branch point of the pipe to each injection valve, even if the pipe length is simply different, or even if the pipe length is the same, due to a difference in layout or a variation in the nozzle hole size of the injection valve, etc. Pressure loss may vary. Therefore, when the urea water is sucked back into the tank by the reverse rotation operation of the pump, it becomes difficult to complete the sucking back of the urea water from each injection valve to the branch point at the same time. When the urea water in one of the paths from the branch point of the pipe to the respective injection valves is sucked back first, the fluid viscosity is lower than that of the urea water remaining in the other path thereafter. The air in the other path is sucked out, and the urea water in the other path may not be sucked back.

  The present invention has been made to solve the above-described problems, and its object is to provide piping connected to each injection valve when the engine is stopped when a plurality of injection valves for injecting urea water are provided. It is an object of the present invention to provide an exhaust treatment device that reliably returns urea water remaining in the tank to the tank.

  An exhaust treatment apparatus according to an aspect of the present invention is provided with an exhaust pipe connected to an engine, an exhaust purification catalyst for purifying nitrogen oxide in exhaust gas, and upstream of the exhaust purification catalyst. A first injection valve and a second injection valve that are provided and inject the urea water into the exhaust pipe by being switched from the closed state to the open state during operation of the engine; Is connected to the tank, and the other end is branched into two in the middle and connected to each of the first injection valve and the second injection valve, and each of the first injection valve and the second injection valve and the tank And a control device for controlling the pump so that the urea water in the first and second injection valves and the pipe is sucked back into the tank after the engine is stopped. With. The control device opens the first injection valve and closes the first injection valve, operates the pump with the second injection valve closed, and closes the first injection valve. The urea water is sucked back into the tank by switching to the second control for operating the pump in a state where the two injection valves are opened.

  If it does in this way, between the 1st injection valve and the tank by performing the 1st control which operates the pump in the state where the 2nd injection valve was closed and the 1st injection valve was opened Of urea water can be sucked back into the tank. Further, the urea water between the second injection valve and the tank is executed by executing the second control for operating the pump with the first injection valve closed and the second injection valve opened. Can be sucked back into the tank. Therefore, the urea water remaining in the first injection valve, the second injection valve and the pipe after the engine is stopped can be sucked back into the tank. Thereby, freezing, deterioration, etc. of urea water in piping can be controlled.

Preferably, the control device executes switching between the first control and the second control a plurality of times.
In this case, the urea water in the pipe connected to the first injection valve and the urea water in the pipe connected to the second injection valve by executing the switching between the first control and the second control a plurality of times. Can be sucked back into the tank step by step. Therefore, urea water can be quickly moved away from the exhaust pipe having a relatively high temperature. Therefore, deterioration of urea water can be suppressed.

  More preferably, after the engine is stopped, the control device first performs control of the first control and the second control in which the temperature of the portion where the injection valve is provided is higher.

  In this case, the urea water is quickly moved away from the exhaust pipe having a relatively high temperature by first executing the control in which the temperature of the portion where the injection valve is provided is higher in the first control and the second control. Can do. Therefore, deterioration of urea water can be suppressed.

  More preferably, the control device opens each of the first injection valve and the second injection valve after the engine is stopped and before executing the first control and the second control. The third control is performed to suck the urea water back into the tank using the pump until the period elapses.

  If it does in this way, urea water can be sucked back in parallel from each of the 1st injection valve and the 2nd injection valve by performing the 3rd control before performing the 1st control. Therefore, the urea water can be quickly moved away from the exhaust pipe having a relatively high temperature. Therefore, deterioration of urea water can be suppressed.

  More preferably, the exhaust pipe includes a first exhaust pipe and a second exhaust pipe connected in parallel to the engine. The first injection valve is provided in the first exhaust pipe. The second injection valve is provided in the second exhaust pipe.

  If it does in this way, the 1st injection valve provided in the 1st exhaust pipe, the 2nd injection valve provided in the 2nd exhaust pipe, piping between each of the 1st injection valve and the 2nd injection valve, and the tank The urea water remaining in the tank can be sucked back into the tank.

  According to the present invention, when a plurality of injection valves for injecting urea water are provided, an exhaust treatment device for reliably returning urea water remaining in a pipe connected to each injection valve to the tank when the engine is stopped is provided. be able to.

It is a figure which shows the structure of an engine and an exhaust-gas treatment apparatus. It is a figure for demonstrating the relationship between piping length and pressure loss. It is a flowchart which shows the content of the control processing performed by a control apparatus. It is a timing chart which shows operation | movement of the urea water pump in this Embodiment, a 1st injection valve, and a 2nd injection valve. It is a timing chart (the 1) which shows operation of the urea water pump in the modification, the 1st injection valve, and the 2nd injection valve. It is a timing chart (the 2) which shows operation of the urea water pump in the modification, the 1st injection valve, and the 2nd injection valve.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. In the following description, the same parts are denoted by the same reference numerals. Their names and functions are also the same. Therefore, detailed description thereof will not be repeated.

  FIG. 1 is a diagram showing a configuration of an exhaust treatment device 2 provided in an engine 10 and an exhaust system in the present embodiment.

  The engine 10 is an internal combustion engine that operates by burning a mixture of fuel and air in a combustion chamber. In the present embodiment, the engine 10 will be described by taking a V-type 6-cylinder diesel engine as an example. Three cylinders are provided in the left and right banks of the engine 10. A first exhaust manifold 12 and a second exhaust manifold 14 are connected to exhaust ports connected to the cylinders of the left and right banks of the engine 10, respectively. One end of a first exhaust pipe 16 is connected to the first exhaust manifold 12. One end of a second exhaust pipe 18 is connected to the second exhaust manifold 14.

  Therefore, the exhaust gas generated when the engine 10 is operated passes through the first exhaust pipe 16 via the first exhaust manifold 12 from the exhaust port and the second exhaust via the second exhaust manifold 14 from the exhaust port. Branches to a route through the pipe 18. The operation of the engine 10 is controlled by the control device 100.

  An exhaust treatment device 2 is provided in the first exhaust pipe 16 and the second exhaust pipe 18. The exhaust treatment device 2 includes a first catalyst 20, a second catalyst 22, a first injection valve 24, a second injection valve 26, a first SCR (Selective Catalytic Reduction) catalyst 28, a second SCR catalyst 30, and urea. A water tank 40, a urea water pump 42, and a connection pipe 50 are included.

  The first catalyst 20, the first injection valve 24, and the first SCR catalyst 28 are provided in the first exhaust pipe 16. The second catalyst 22, the second injection valve 26, and the second SCR catalyst 30 are provided in the second exhaust pipe 18.

  The first catalyst 20 and the second catalyst 22 are oxidation catalysts such as DOC (Diesel Oxidation Catalyst), for example. A DPF (Diesel Particulate filter) that collects particulate matter in the exhaust gas may be provided downstream of the first catalyst 20 and the second catalyst 22.

  The first SCR catalyst 28 purifies the exhaust gas flowing through the first exhaust pipe 16 from the engine 10 by reducing nitrogen oxides such as NOx using urea water injected (added) from the first injection valve 24. . The second SCR catalyst 30 purifies exhaust gas flowing through the second exhaust pipe 18 from the engine 10 by reducing nitrogen oxides using urea water injected (added) from the second injection valve.

  The urea water tank 40 stores urea water to be supplied to each of the first injection valve 24 and the second injection valve 26. The urea water tank 40 and each of the first injection valve 24 and the second injection valve 26 are connected by a connection pipe 50. One end of the connection pipe 50 is connected to the urea water tank 40. The other end of the connection pipe 50 branches into two on the way and is connected to each of the first injection valve and the second injection valve.

  Specifically, the connection pipe 50 includes a first pipe 44, a second pipe 46, and a third pipe 48. One end of a third pipe 48 is connected to the urea water tank 40. One end of the first pipe 44 and one end of the second pipe 46 are connected to the other end of the third pipe 48. Hereinafter, a connection point between one end of the first pipe 44, one end of the second pipe 46, and the other end of the third pipe 48 is referred to as a branch point 52. The first injection valve 24 is connected to the other end of the first pipe 44. The second injection valve 26 is connected to the other end of the second pipe 46.

  The urea water tank 40 is provided with a urea water pump 42 for supplying urea water in the urea water tank 40 to the first injection valve 24 and the second injection valve 26. The urea water pump 42 is, for example, an electric pump that operates using a motor or the like. By operating the urea water pump 42, urea water can be circulated between the urea water tank 40 and each of the first injection valve 24 and the second injection valve 26. The urea water pump 42 is an operation for pumping urea water from the urea water tank 40 toward the third pipe 48 in accordance with a control signal from the control device 100 (hereinafter, such an operation is described as a normal rotation operation). And an operation of sucking back urea water from the third pipe 48 toward the urea water tank 40 (hereinafter, such operation is referred to as reverse operation).

  The first injection valve 24 is provided at a position between the first catalyst 20 and the first SCR catalyst 28 in the first exhaust pipe 16. The first injection valve 24 is switched from one of the valve open state and the valve closed state to the other state by driving an internal valve body in accordance with a control signal from the control device 100. When the first injection valve 24 is opened, the first exhaust pipe 16 and the first pipe 44 are in communication. At this time, when urea water is pumped from the urea water tank 40 by the urea water pump 42, the urea water flows from the urea water tank 40 via the third pipe 48 and the first pipe 44, and the first injection. The fuel is injected from the valve 24 into the first exhaust pipe 16. When the first injection valve 24 is closed, the inside of the first exhaust pipe 16 and the first pipe 44 are cut off, and the urea water injection from the first injection valve 24 is stopped.

  The second injection valve 26 is provided at a position between the second catalyst 22 and the second SCR catalyst 30 in the second exhaust pipe 18. The second injection valve 26 is switched from one of the valve open state and the valve closed state to the other state when the internal valve body is driven in accordance with a control signal from the control device 100. When the second injection valve 26 is opened, the second exhaust pipe 18 and the second pipe 46 are in communication. At this time, when urea water is pumped from the urea water tank 40 by the urea water pump 42, the urea water flows from the urea water tank 40 via the third pipe 48 and the second pipe 46, and the second injection. The fuel is injected from the valve 26 into the second exhaust pipe 18. When the second injection valve 26 is in the closed state, the inside of the second exhaust pipe 18 and the second pipe 46 are cut off, so that the urea water injection from the second injection valve 26 is stopped.

  In the present embodiment, it is assumed that both the first injection valve 24 and the second injection valve 26 are in a closed state when the valve element is not driven (non-energized).

  The control device 100 is configured to include a CPU (Central Processing Unit), a memory, an input / output buffer, and the like, although not shown. The control device 100 controls various devices so that the engine 10 and the exhaust treatment device 2 are in a desired operating state based on signals from each sensor and device, and a map and program stored in the memory. Various controls are not limited to processing by software, and can be processed by dedicated hardware (electronic circuit).

  The IG switch 102 is an operation member for the user to start or stop the engine 10. For example, when the IG switch 102 is operated by the user while the engine 10 is operating, the control device 100 starts a stop process of the engine 10 and puts the engine 10 into a stopped state. Further, for example, when the IG switch 102 is operated by the user while the engine 10 is stopped, the control device 100 starts the startup process of the engine 10 and puts the engine 10 into an operating state.

  In the exhaust treatment device 2 having the above-described configuration, during operation of the engine 10, the urea water pump 42 operates so that the pressure of the urea water in the connection pipe 50 becomes equal to or higher than a predetermined pressure. The first injection valve 24 and the second injection valve 26 are at a predetermined timing (for example, timing when the exhaust gas temperature falls within a temperature range in which the nitrogen oxides can be reduced in the first SCR catalyst 28 and the second SCR catalyst 30). The valve opens. As a result, urea water is injected from the first injection valve 24 into the first exhaust pipe 16, whereby nitrogen oxides are reduced in the first SCR catalyst 28. Further, nitrogen oxide is reduced in the second SCR catalyst 30 by injecting urea water from the second injection valve 26 into the second exhaust pipe 18.

  On the other hand, when this urea water falls below about -11 degreeC, it may freeze. For this reason, if the urea water freezes in a low temperature environment while the engine 10 is stopped, the inside of the connection pipe 50 is clogged with the frozen urea water, which hinders the injection of urea water at the next engine start. Moreover, since urea water has the characteristic of degrading at high temperatures, deterioration may be accelerated if the urea water is maintained in a high temperature state when the engine is stopped after a high load operation.

  Therefore, when the engine 10 stops, it is conceivable that the urea water pump 42 is reversely operated to suck back the urea water in the connection pipe 50.

  However, as shown in FIG. 1, a part of the piping, a pump, and a tank are shared by the plurality of injection valves by, for example, branching the pipe halfway and connecting to each of the plurality of injection valves. In this case, the urea water in the connection pipe 50 may not be sucked back even if the urea water pump 42 is operated in reverse. This is due to differences in piping length and layout in the path from the branch point 52 to each injection valve.

  In the path from the branch point 52 to each injection valve, even if the pipe length is simply different, or even if the pipe length is the same, the pressure loss is caused by the difference in layout or the variation in the injection hole size. May be different.

  FIG. 2 is a diagram illustrating the relationship between the layout of the pipe, the pipe length, and the pressure loss. The vertical axis in FIG. 2 indicates the magnitude of pressure loss. The horizontal axis in FIG. 2 indicates the pipe length. The solid line in FIG. 2 shows the relationship between the pipe length and the pressure loss in the case of the layout of the pipe path A (defined by the number of bends and the like). 2 indicates the relationship between the piping length and the pressure loss in the case of the layout of the piping route B (for example, the number of bendings is larger than that of the piping route A).

  As shown in FIG. 2, for example, when the pipe length is different even in the same pipe path A (that is, the number of bends is the same), the pressure loss increases as the pipe length increases. On the other hand, if the layout (number of bends) is different even with the same pipe length, the pressure loss is different. Therefore, if the pipe length and layout are different as in the first pipe 44 (pipe path A and pipe length La) and the second pipe 46 (pipe path B and pipe length Lb), the pressure loss The difference (Pb−Pa) is greatly different.

  Therefore, when the urea water is sucked back into the urea water tank 40 by the reverse operation of the urea water pump 42, it becomes difficult to complete the sucking back of the urea water from each injection valve to the branch point 52 at the same time. Moreover, when the urea water in one of the paths from the branch point 52 to each injection valve is sucked back first, one of the fluid viscosity lower than that of the urea water remaining in the other path is thereafter obtained. Air in the path is sucked out, and urea water in the other path cannot be sucked back.

  Therefore, in the present embodiment, after the engine 10 is stopped, the control device 100 opens the first injection valve 24 and closes the second injection valve 26 in the urea water pump 42. By switching between the first control for operating the first injection valve 24 and the second control for operating the urea water pump 42 with the first injection valve 24 closed and the second injection valve 26 open. Suck water back into tank.

  In this way, the urea water of both the first pipe 44 and the second pipe 46 can be returned to the urea water tank 40 after the engine 10 is stopped.

  With reference to FIG. 3, the control process performed by the control apparatus 100 of the exhaust processing apparatus 2 which concerns on this Embodiment is demonstrated.

  In step (hereinafter, step is referred to as S) 100, control device 100 determines whether or not IG is turned off. For example, control device 100 determines that IG is turned off when engine 10 is stopped by operating IG switch 102 during operation of engine 10. If it is determined that IG is turned off (YES in S100), the process proceeds to S102.

  In S102, control device 100 causes urea water pump 42 to perform a reverse operation. In S104, control device 100 opens first injection valve 24. At this time, the second injection valve 26 is maintained in a closed state.

  In S106, control device 100 determines whether or not the first period has elapsed since first injection valve 24 was opened. The first period may be a predetermined period, or may be a period set based on the temperature of the urea water, the temperature of the first exhaust pipe 16, or the like. If it is determined that the first period has elapsed (YES in S106), the process proceeds to S108.

  In S108, control device 100 switches the injection valve to be opened. For example, when the first injection valve 24 is in the open state and the second injection valve 26 is in the closed state, the control device 100 sets the first injection valve 24 in the closed state and sets the first injection valve 24 in the closed state. 2 The injection valve 26 is opened. For example, when the first injection valve 24 is in the closed state and the second injection valve 26 is in the open state, the control device 100 opens the first injection valve 24 and sets the first injection valve 24 in the open state. 2 The injection valve 26 is closed.

  In S110, control device 100 determines whether or not a predetermined time has elapsed since the injection valve was switched. For example, when the first injection valve 24 is in the closed state and the second injection valve 26 is in the open state, the control device 100 switches the injection valve from the time when the injection valve to be opened is switched. It is determined whether two periods have elapsed. For example, when the first injection valve 24 is in the open state and the second injection valve 26 is in the closed state, the control device 100 changes the first injection valve from when the injection valve to be opened is switched. It is determined whether or not one period has elapsed. The second period may be a predetermined period, or may be a period set based on the temperature of the urea water, the temperature of the second exhaust pipe 18, or the like. In the present embodiment, a case where the first period and the second period are the same period will be described as an example.

  In S112, control device 100 determines whether an end condition is satisfied. The end condition is, for example, a condition that a predetermined time (for example, a time of about several tens of seconds) has elapsed from the time when the reverse rotation operation of the urea water pump 42 is started (that is, when the engine 10 is stopped). Alternatively, it may be a condition that the number of executions of the opening operation of the first injection valve 24 is equal to or greater than a predetermined number, or the number of executions of the opening operation of the second injection valve 26 may be in advance. It may be a condition that the predetermined number of times has been reached, or a condition that the amount of urea water in the urea water tank 40 has increased by a threshold value or more. If the termination condition is satisfied (YES in S112), the process proceeds to S114.

  In S114, control device 100 stops the reverse rotation operation of urea water pump 42. In S116, control device 100 closes both first injection valve 24 and second injection valve 26.

  If it is determined that IG is not turned off (NO in S100), the process returns to S100. If it is determined in S106 that the first period has not elapsed (NO in S106), the process returns to S106. Furthermore, when it is determined in S110 that the predetermined time has not elapsed (NO in S110), the process returns to S110. Further, if it is determined that the end condition is not satisfied (NO in S112), the process is returned to S108, and the injection valve to be opened is switched.

  The operation of the exhaust treatment apparatus 2 according to the present embodiment based on the above structure and flowchart will be described with reference to FIG. FIG. 4 is a timing chart showing the operations of the urea water pump 42, the first injection valve 24, and the second injection valve 26 in the present embodiment.

  For example, it is assumed that the urea water pump 42 is in a stopped state and both the first injection valve 24 and the second injection valve 26 are closed.

  When engine 10 is stopped by the driver's IG operation at time T (0) (YES in S100), the reverse operation of urea water pump 42 is started (S102). The reverse operation of the urea water pump 42 is started, and the first injection valve 24 is opened (S104).

  Since the first injection valve 24 is in the open state and the second injection valve 26 is in the closed state, the urea water in the first pipe 44 and the third pipe 48 is converted into urea water by the reverse operation of the urea water pump 42. It is sucked back into the tank 40.

  If it is determined at time T (1) that the first period has elapsed from time T (0) (YES at S106), the valve-opening injector is changed from first injector 24 to second injector 26. (S108). That is, the first injection valve 24 is closed and the second injection valve 26 is opened. Therefore, the urea water in the second pipe 46 and the third pipe 48 is sucked back into the urea water tank 40 by the reverse operation of the urea water pump 42.

  After the time T (2), the first injection valve 24 is in the open state in the period from the time T (2) to the time T (3) and the period from the time T (4) to the time T (5). At the same time, the second injection valve 26 is closed. During this period, the urea water in the first pipe 44 and the third pipe 48 is sucked back into the urea water tank 40 by the reverse operation of the urea water pump 42.

  On the other hand, in the period from time T (3) to time T (4) and the period from time T (5) to time T (6), the first injection valve 24 is closed and the second injection valve 26 is closed. Is opened. Therefore, the urea water in the second pipe 46 and the third pipe 48 is sucked back into the urea water tank 40 by the reverse operation of the urea water pump 42.

  If it is determined at time T (6) that the second period has elapsed (YES in S110) and it is determined that the end condition is satisfied (YES in S112), the operation of urea water pump 42 is performed. While being stopped (S114), each of the first injection valve 24 and the second injection valve 26 is closed (S116).

  As described above, according to the exhaust gas treatment apparatus of the present embodiment, the urea water pump 42 is reversely rotated with the second injection valve 26 closed and the first injection valve 24 opened. By performing the first control to be operated, the urea water in the first pipe 44 and the third pipe 48 between the first injection valve 24 provided in the first exhaust pipe 16 and the urea water tank 40 is supplied to the urea water tank. 40 can be sucked back. Further, the second exhaust pipe 18 is executed by executing the second control that reversely operates the urea water pump 42 with the first injection valve 24 closed and the second injection valve 26 opened. The urea water in the second pipe 46 and the third pipe 48 between the second injection valve 26 and the urea water tank 40 provided on the urea water tank 40 can be sucked back into the urea water tank 40. Therefore, urea water remaining in the connection pipe 50 after the engine 10 is stopped can be sucked back into the urea water tank 40. Thereby, freezing, deterioration, etc. of urea water in piping can be controlled. Therefore, when a plurality of injection valves for injecting urea water are provided, it is possible to provide an exhaust treatment device that reliably returns the urea water remaining in the pipe connected to each injection valve to the tank when the engine is stopped. .

  Further, the first control and the second control are switched and executed a plurality of times, so that the urea water in the first pipe 44 connected to the first injection valve 24 and the second pipe connected to the second injection valve 26. The urea water in 46 can be returned to the urea water tank 40 step by step. Therefore, it is possible to suppress the urea water from being affected by the heat of the exhaust pipe.

Hereinafter, modified examples will be described.
In the above-described embodiment, the first period for executing the first control and the second period for executing the second control are described as being the same period. However, the first period and the second period are different. It may be.

  For example, the first period and the second period may be set based on the difference between the pipe length of the first pipe 44 and the pipe length of the second pipe 46. Alternatively, the first period and the second period may be set based on the difference between the number of bends of the first pipe 44 and the number of bends of the second pipe 46. In addition, as described with reference to FIG. 2, the first period and the second period may be set based on the difference between the pressure loss of the first pipe 44 and the pressure loss of the second pipe 46. Further, the first period and the second period are set so that the execution period of the control corresponding to one of the first pipe 44 and the second pipe 46 that is easily affected by the exhaust pipe is longer than the other period. May be.

  Alternatively, the first period and the second period may be set so that the ratio at which the urea water is sucked back in the first pipe 44 and the ratio at which the urea water is sucked back in the second pipe 46 are the same. The rate at which urea water is sucked back in the first pipe 44 is the first period with respect to the total amount of urea water in the first pipe 44, assuming that the first pipe 44 is filled with urea water. Indicates the amount of urea water sucked back. The rate at which urea water is sucked back in the second pipe 46 is the second period with respect to the total amount of urea water in the second pipe 46, assuming that the second pipe 46 is filled with urea water. Indicates the amount of urea water sucked back.

  FIG. 5 is a timing chart (part 1) illustrating operations of the urea water pump 42, the first injection valve 24, and the second injection valve 26 in the modification. In FIG. 5, during the reverse rotation period of the urea water pump 42 after the engine 10 is stopped (T (7) to T (15)), the first period (T (7) to T (8), T (9) to T (10), T (11) to T (12), T (13) to T (14)), and the second injection valve 26 is in the open state. Half period of the second period (T (8) to T (9), T (10) to T (11), T (12) to T (13), T (14) to T (15)) The operation of the first injection valve 24 and the second injection valve 26 when set to become is shown.

  As described above, by appropriately setting the first period and the second period, the urea water in the vicinity of the first injection valve 24 and the vicinity of the second injection valve 26 can be quickly sucked back. Therefore, it is possible to suppress deterioration of the urea water due to the influence of heat from the first exhaust pipe 16 and the second exhaust pipe 18 after the engine 10 is stopped.

  In the above-described embodiment, during the reverse operation of the urea water pump 42, the first control for opening only the first injection valve 24, and the second control for opening only the second injection valve 26, Although the description has been made on the assumption that they are executed alternately, for example, before the first control and the second control are alternately executed after the engine is stopped, each of the first injection valve and the second injection valve is opened. You may perform 3rd control which makes a state.

  Such control can be realized, for example, by adding a process of opening the first injection valve and the second injection valve 26 until the third period elapses before the process of S104 in the flowchart of FIG.

  FIG. 6 is a timing chart (part 2) showing operations of the urea water pump 42, the first injection valve 24, and the second injection valve 26 in the modification. As shown in FIG. 6, the first injection valve 24 and the second injection valve 26 are maintained until the third period elapses (T (17)) from the time when the reverse rotation operation of the urea water pump 42 is started (T (16)). Since the operation after the time T (17) is the same as the operation after the time T (0) in Fig. 4, detailed description thereof will not be repeated.

  In this way, urea water can be sucked back from each of the first injection valve 24 and the second injection valve 26 in parallel. Therefore, the urea water can be quickly moved away from the exhaust pipe having a relatively high temperature immediately after the engine is stopped. Therefore, deterioration of urea water can be suppressed. The third period is set so that, for example, all of the urea water in the pipe having the smaller residual amount of urea water in the first pipe 44 and the second pipe 46 is not sucked back.

  In the above-described embodiment, the first control and the second control are executed after the engine is stopped. For example, after the engine is stopped, the injection valve is provided in the first control and the second control. You may perform control with the one where the temperature of a location is higher first.

  In this way, the urea water can be quickly moved away from the exhaust pipe having a relatively high temperature after the engine is stopped. Therefore, deterioration of urea water can be suppressed.

  Note that the higher temperature at the location where the injection valve is provided may be fixedly set by experiment or the like, or may be actually measured using temperature sensors of the first exhaust pipe 16 and the second exhaust pipe 18. It may be set based on the value or the estimated value from the operation history of the engine 10.

  In the above-described embodiment, the first control and the second control are switched and executed a plurality of times after the engine is stopped. For example, the first control and the second control are performed once each after the engine is stopped. It may be executed.

  Further, in the above-described embodiment, it has been described that the first control and the second control are executed the same number of times during the reverse operation of the urea water pump 42. However, the first period and the second period are the same period. However, the number of times of execution of the first control may be different from the number of times of execution of the second control. For example, the number of executions of the first control and the number of executions of the second control may be set so that the ratio of the urea water sucked back during a predetermined period is the same.

  By appropriately setting the number of executions in this manner, urea water in the vicinity of the first injection valve 24 and the second injection valve 26 can be quickly sucked back. Therefore, it is possible to suppress deterioration of the urea water due to the influence of heat from the first exhaust pipe 16 and the second exhaust pipe 18 after the engine 10 is stopped.

  Furthermore, in the above-described embodiment, the first period for executing the first control during the reverse rotation operation of the urea water pump 42 and the second period for executing the second control have been described as being invariant. During the reverse operation of the urea water pump 42, the first period of the first control may be different from the first period of the first control executed immediately before. Similarly, during the reverse operation of the urea water pump 42, the second period of the second control may be different from the second period of the second control executed immediately before. For example, the first period and the second period may be set short immediately after the engine is stopped, and the first period and the second period may be set long after a predetermined time has elapsed since the engine was stopped. If it does in this way, immediately after an engine stop, the urea water of both the 1st injection valve 24 vicinity and the 2nd injection valve 26 vicinity can be quickly sucked back.

  In the above-described embodiment, the first injection valve 24 and the second injection valve 26 are described as being provided in different exhaust pipes connected to the engine 10, respectively, but the first injection valve 24 and the second injection valve 26 are described. May be provided in the same exhaust pipe.

  In the above-described embodiment, the engine 10 has been described using the V-type engine as an example, but may be a horizontally opposed engine or an in-line engine, for example.

In addition, you may implement combining the above-mentioned modification, all or one part.
The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

  2 exhaust treatment device, 10 engine, 12 first exhaust manifold, 14 second exhaust manifold, 16 first exhaust pipe, 18 second exhaust pipe, 20 first catalyst, 22 second catalyst, 24 first injection valve, 26 first 2 injection valves, 28 1st SCR catalyst, 30 2nd SCR catalyst, 40 urea water tank, 42 urea water pump, 44 1st piping, 46 2nd piping, 48 3rd piping, 50 connection piping, 52 branch point, 100 control device 102 IG switch.

Claims (5)

An exhaust pipe connected to the engine;
An exhaust purification catalyst provided in the exhaust pipe for purifying nitrogen oxides in the exhaust gas;
A first injection valve and a second injection valve which are provided upstream of the exhaust purification catalyst and inject urea water into the exhaust pipe by being switched from a closed state to an open state during operation of the engine;
A tank for storing the urea water;
A pipe having one end connected to the tank and the other end branched into two in the middle and connected to each of the first injection valve and the second injection valve;
A pump for circulating the urea water via the pipe between each of the first injection valve and the second injection valve and the tank;
A control device for controlling the pump so that the urea water in the pipe is sucked back into the tank after the engine is stopped;
The control device includes: a first control that operates the pump in a state where the first injection valve is in the open state and the second injection valve is in the closed state; and Exhaust gas that sucks the urea water back into the tank by performing a plurality of times of switching to the second control for operating the pump in a state in which the second injection valve is in the open state with the valve closed. Processing equipment. The control device executes the first control until a first period elapses, executes the second control until a second period elapses,
In the first period and the second period, the ratio of urea water sucked back in the first portion of the pipe from the first injection valve to the branch point and the pipe from the second injection valve to the branch point The exhaust treatment device according to claim 1, wherein the exhaust water treatment device is set so that the ratio of the urea water sucked back in the second portion is the same.   3. The control device according to claim 1, wherein, after the engine is stopped, the control device executes the control in which the temperature of the portion where the injection valve is provided is higher among the first control and the second control. Exhaust treatment device.   The control device sets each of the first injection valve and the second injection valve to the open state after the engine is stopped and before the first control and the second control are executed. The exhaust treatment device according to any one of claims 1 to 3, wherein a third control is performed to suck the urea water back into the tank using the pump until a third period elapses. The exhaust pipe includes a first exhaust pipe and a second exhaust pipe connected in parallel to the engine,
The first injection valve is provided in the first exhaust pipe,
The exhaust treatment device according to any one of claims 1 to 4, wherein the second injection valve is provided in the second exhaust pipe.

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