JP6574154B2 - Exhaust treatment device - 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 includes an exhaust pipe connected to an engine, an exhaust purification catalyst provided in the exhaust pipe for purifying nitrogen oxides in exhaust gas, and an exhaust purification catalyst in the exhaust pipe The first injection valve and the second injection valve that are provided in the upstream portion of the engine and inject the urea water into the exhaust pipe by switching from the valve closed state to the valve open state during operation of the engine, and store the urea water. A tank, a pipe having one end connected to the tank, a pipe having the other end branched into two from a halfway branch point and connected to each of the first injection valve and the second injection valve, and a branch point of the pipe A flow rate adjusting valve provided on at least one of the first path to the first injection valve and the second path from the branch point to the second injection valve, and capable of adjusting the passage cross-sectional area of the path; Each of the first injection valve and the second injection valve After the engine is stopped and the pump for circulating urea water via the pipe between the first and second injection valves, both the first injection valve and the second injection valve are opened, and the first path and the second path And a control device for controlling the pump so as to suck the urea water in the tank back into the tank. The control device includes a first period from the start of the pump operation until the urea water in the first path is sucked back to the branch point, and the urea water in the second path branches from the start of the pump operation. The passage cross-sectional area is adjusted using the flow rate adjustment valve so that the second period until it is sucked back to the point becomes the same.

  In this way, after the engine is stopped, the passage cross-sectional area is adjusted so that the first period and the second period become the same, so the urea water from the first injection valve to the branch point and the second injection valve The urea water up to the branch point can be sucked back into the tank in parallel. Therefore, freezing and deterioration of urea water in the pipe can be suppressed.

  Preferably, the exhaust treatment device is provided on the first path, the first pressure sensor for detecting the first pressure in the first path, and the second pressure in the second path provided on the second path. And a second pressure sensor for detecting pressure. The flow rate adjusting valve is provided between at least one of the first pressure sensor and the first injection valve and between the second pressure sensor and the second injection valve. The control device adjusts the passage sectional area using the flow rate adjustment valve so that the difference or ratio between the first pressure and the second pressure becomes a predetermined value.

  In this way, when the urea water in the first path and the second path is sucked back into the tank using the pump after the engine is stopped, the passage is cut off so that the first period and the second period are the same. The area can be adjusted.

  More preferably, the exhaust treatment device is provided on the first path, and is provided on the second path, the first flow sensor for detecting the first flow rate of the urea water in the first path, and the second path. And a second flow rate sensor for detecting the second flow rate of the urea aqueous solution. The flow rate adjusting valve is provided between at least one of the first flow rate sensor and the first injection valve and between the second flow rate sensor and the second injection valve. The control device adjusts the passage sectional area using the flow rate adjusting valve so that the difference or ratio between the first flow rate and the second flow rate becomes a predetermined value.

  In this way, when the urea water in the first path and the second path is sucked back into the tank using the pump after the engine is stopped, the passage is cut off so that the first period and the second period are the same. The area can be adjusted.

  More preferably, the predetermined value is set based on the volume of urea water in the first path and the volume of urea water in the second path.

  In this way, when the urea water in the first path and the second path is sucked back into the tank using the pump after the engine is stopped, the passage is cut off so that the first period and the second period are the same. The area can be adjusted.

  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.

  Thus, after the engine is stopped, the first injection valve provided in the first exhaust pipe, the second injection valve provided in the second exhaust pipe, each of the first injection valve and the second injection valve, and the tank The urea water remaining in the pipe between the two 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 an example of the change of the pressure in piping using a flow control valve. It is a timing chart which shows an example of operation of urea water pump and a flow regulating valve in this embodiment, and change of differential pressure deltaP. It is a flowchart which shows the content of the control processing performed by the control apparatus in a modification.

  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, a connection pipe 50, a first pressure sensor 54, a second pressure sensor 56, and a flow rate adjustment valve 58 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 24 and the second injection valve 26.

  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 flow rate adjusting valve 58 is provided on at least one of the first pipe 44 and the second pipe 46 that has a smaller pressure loss. In the present embodiment, it is assumed that the pressure loss in the first pipe 44 is smaller than the pressure loss in the second pipe 46. Therefore, in the present embodiment, the flow rate adjustment valve 58 is provided in the first pipe 44. The flow rate adjustment valve 58 is provided between the first pressure sensor 54 and the first injection valve 24. The flow rate adjusting valve 58 is an on-off valve that can adjust the passage cross-sectional area by driving a valve body in accordance with a control signal from the control device 100. The flow rate adjustment valve 58 may be, for example, a solenoid valve that drives a valve body using a solenoid or the like.

  The first pressure sensor 54 is provided between the flow rate adjustment valve 58 and the branch point 52. The first pressure sensor 54 detects a pressure (hereinafter referred to as a first pressure) P1 in the first pipe 44. The first pressure sensor 54 outputs a signal indicating the detected first pressure P <b> 1 to the control device 100.

  The second pressure sensor 56 is provided in the second pipe 46. The second pressure sensor 56 detects a pressure (hereinafter referred to as a second pressure) P2 in the second pipe 46. The second pressure sensor 56 outputs a signal indicating the detected second pressure P2 to the control device 100.

  The IG switch 102 is an operation member for the user to start or stop the engine 10.

  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).

  A first pressure sensor 54 and a second pressure sensor 56 are connected to the control device 100. Based on the reception results of the signals transmitted from the first pressure sensor 54, the second pressure sensor 56, and the IG switch 102, the control device 100 performs the engine 10, the urea water pump 42, the first injection valve 24, the second injection valve. 26 and the flow rate adjusting valve 58 are controlled.

  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 configuration, during the operation of the engine 10, the urea water pump 42 is rotated forward 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. Therefore, if the urea water freezes in a low temperature environment while the engine 10 is stopped, the inside of the connection pipe 50 becomes clogged with the frozen urea water, which causes a hindrance to the urea water injection 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. When the urea water in one of the paths from the branch point 52 to each injection valve has been sucked back first, one of the fluids having a lower fluid viscosity than the urea water remaining in the other path is thereafter used. 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 both the first injection valve 24 and the second injection valve 26 so that the branch point 52 and the first injection valve 24 The urea water pump 42 is controlled so that the urea water in the first pipe 44 and the second pipe 46 between the branch point 52 and the second injection valve 26 are sucked back into the urea water tank 40. Further, the control device 100 starts the operation of the urea water pump 42 during the first period from the start of the operation of the urea water pump 42 until the urea water in the first pipe 44 is sucked back to the branch point 52. The position where the flow rate adjustment valve 58 of the first pipe 44 is provided using the flow rate adjustment valve 58 so that the second period from when the urea water in the second pipe 46 is sucked back to the branch point 52 becomes the same. Adjust the cross-sectional area of the passage.

  In this way, after the engine 10 is stopped, the passage cross-sectional area of the flow rate adjustment valve 58 is adjusted so that the first period and the second period become the same, so the urea water in the first pipe 44 and the second The urea water in the pipe 46 can be sucked back into the urea water tank 40 in parallel.

  In the present embodiment, the control device 100 adjusts the passage sectional area using the flow rate adjustment valve 58 so that the difference between the first pressure P1 and the second pressure P2 becomes a predetermined value. The predetermined value is set based on the urea water capacity in the first pipe 44 and the urea water capacity in the second pipe 46.

  In the present embodiment, it is assumed that the amount of urea water in the first pipe 44 and the amount of urea water in the second pipe 46 are the same. In this case, by setting the first pressure and the second pressure to the same pressure, the flow rate from the first pipe 44 to the third pipe 48 and the flow rate from the second pipe 46 to the third pipe 48 at the time of sucking back Can be the same amount. Therefore, the predetermined value is, for example, zero. That is, in the present embodiment, the control device 100 adjusts the flow rate adjustment valve 58 so that the differential pressure ΔP obtained by subtracting the second pressure P2 from the first pressure P1 becomes zero.

  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 and second injection valve 26.

  In S106, control device 100 acquires first pressure P1 and second pressure P2 using first pressure sensor 54 and second pressure sensor 56. In S108, control device 100 calculates differential pressure ΔP by subtracting second pressure P2 from first pressure P1.

  In S110, control device 100 determines whether or not differential pressure ΔP is zero. If it is determined that differential pressure ΔP is not zero (NO in S110), the process proceeds to S112.

  In S112, control device 100 executes adjustment control. Specifically, the control device 100 reduces the opening degree of the flow rate adjustment valve 58 by a predetermined value. Note that the initial value of the opening degree of the flow rate adjustment valve 58 is a value (100%) corresponding to full opening.

  The pressure loss in the first pipe 44 can be increased by reducing the opening of the flow rate adjustment valve 58 during the reverse operation of the urea water pump 42. Therefore, the magnitude of the first pressure P1 in the first pipe 44 can be increased in the negative direction. Thereby, the differential pressure ΔP can be brought close to zero.

  For example, if the first pressure P1 shown by the solid line in FIG. 4 is made the same as the second pressure P2 shown by the one-dot chain line in FIG. 4 by adjusting the opening of the flow regulating valve 58, the differential pressure ΔP is made zero. Can do.

  In S114, control device 100 calculates differential pressure ΔP. In S116, control device 100 determines whether or not calculated differential pressure ΔP is zero. If it is determined that calculated differential pressure ΔP is zero (YES in S116), the process proceeds to S118. In S118, control device 100 ends the adjustment control, and moves the process to S120.

  In S120, 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, the condition may be 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 S120), the process proceeds to S122.

  In S122, control device 100 stops the reverse rotation operation of urea water pump 42. In S124, control device 100 closes both first injection valve 24 and second injection valve 26. At this time, the control device 100 may return the opening degree of the flow rate adjustment valve 58 to the initial value.

  If it is determined that IG is not turned off (NO in S100), the process returns to S100. If it is determined in S110 that differential pressure ΔP is zero (YES in S110), the process proceeds to S120. Furthermore, when it is determined in S116 that differential pressure ΔP is not zero (NO in S116), the process proceeds to S112. Further, if it is determined that the end condition is not satisfied (NO in S120), the process returns to S120 and waits until the end condition is satisfied.

  The operation of the exhaust treatment apparatus 2 according to the present embodiment based on the above-described structure and flowchart will be described with reference to FIG. FIG. 5 is a timing chart showing the operation of the urea water pump 42 and the flow rate adjusting valve 58 and the change in the differential pressure ΔP in the present embodiment.

  For example, the urea water pump 42 is stopped, the first injection valve 24 and the second injection valve 26 are both closed, and the flow rate adjustment valve 58 is fully open (100%). Assume a certain case.

  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 and the second injection valve 26 are opened (S104).

  The first pressure P1 and the second pressure P2 are acquired using the first pressure sensor 54 and the second pressure sensor 56 (S106), and the second pressure P2 is subtracted from the first pressure P1 to calculate the differential pressure ΔP. (S108). If calculated differential pressure ΔP is not zero (NO in S110), adjustment control is executed (S112). By executing the adjustment control, the opening degree of the flow rate adjustment valve 58 is decreased. Then, differential pressure ΔP is calculated again (S114), and execution of adjustment control and calculation of differential pressure ΔP are repeated until calculated differential pressure ΔP becomes zero (NO in S116).

  When calculated differential pressure ΔP becomes zero at time T (1) (YES in S116), the adjustment control is terminated (S118), and it is determined whether or not the termination condition is satisfied (S120). Thereafter, the reverse operation of the urea water pump 42 is continued while the state where the differential pressure ΔP becomes zero, so that the urea water between the first injection valve 24 and the branch point 52 and the second injection valve 26 are maintained. And the urea water between the branch points 52 are sucked back into the urea water tank 40 in parallel. After the suction back of the urea water between the first injection valve 24 and the branch point 52 and the urea water between the second injection valve 26 and the branch point 52 is completed, the urea water in the third pipe 48 is removed. It is sucked back into the urea water tank 40.

  If it is determined at time T (2) that the termination condition is satisfied after all of the urea water in connection pipe 50 has been sucked back into urea water tank 40 (YES in S120), operation of urea water pump 42 is performed. While being stopped (S122), each of the first injection valve 24 and the second injection valve 26 is closed (S124).

  As described above, according to the exhaust treatment apparatus according to the present embodiment, after the engine 10 is stopped, the passage sectional area is adjusted by using the flow rate adjustment valve 58 so that the differential pressure ΔP becomes zero. The pressure loss can be made the same between the first pipe 44 and the second pipe 46. Thereby, the flow rate from the first pipe 44 to the third pipe 48 and the flow rate from the second pipe 46 to the third pipe 48 can be made the same. Since the amount of urea water in the first pipe 44 and the amount of urea water in the second pipe 46 are the same, the urea water in the first pipe 44 is sucked back from the first injection valve 24 to the branch point 52. The first period during which the urea water in the second pipe 46 is sucked back from the second injection valve 26 to the branch point 52 can be made the same. Accordingly, the urea water from the first injection valve 24 to the branch point 52 and the urea water from the second injection valve 26 to the branch point 52 can be sucked back into the urea water tank 40 in parallel. Therefore, freezing and deterioration of urea water in the pipe can be suppressed. 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. .

Hereinafter, modified examples will be described.
In the above-described embodiment, on the assumption that the urea water capacity in the first pipe 44 and the urea water capacity in the second pipe 46 are the same, the flow rate adjustment valve so that the differential pressure ΔP becomes zero. However, in consideration of a certain margin, for example, the flow rate adjustment valve 58 may be controlled so that the magnitude of the differential pressure ΔP is equal to or less than a threshold value (a value greater than zero). .

  Furthermore, in the above-described embodiment, assuming that the urea water capacity in the first pipe 44 and the urea water capacity in the second pipe 46 are the same, the flow rate is set so that the differential pressure ΔP becomes zero. Although the control valve 58 has been described as being controlled, the capacity of urea water in the first pipe 44 and the capacity of urea water in the second pipe 46 may be different.

  In this case, the control device 100 controls the flow rate adjustment valve 58 so that the difference between the first pressure P1 and the second pressure P2 becomes a predetermined value. The predetermined value is set so that the first period and the second period are the same based on the capacity of urea water in the first pipe 44 and the capacity of urea water in the second pipe 46. Is done. For example, when the capacity of urea water in the second pipe 46 is larger than the capacity of urea water in the first pipe 44, the flow rate from the second pipe 46 to the third pipe 48 is increased from the first pipe 44 to the third pipe. A predetermined value is set such that the first pressure P1 is lower than the second pressure P2 so as to be larger than the flow rate to 48.

  Further, in the above-described embodiment, it has been described that the flow rate adjustment valve 58 is controlled so that the difference between the first pressure P1 and the second pressure P2 becomes a predetermined value. For example, the first pressure P1 The flow rate adjustment valve 58 may be controlled so that the ratio between the first pressure P2 and the second pressure P2 becomes a predetermined value.

  The predetermined value in this case is set based on the volume ratio between the urea water capacity in the first pipe 44 and the urea water capacity in the second pipe 46.

  For example, when the passage sectional area of the first pipe 44 and the passage sectional area of the second pipe 46 are the same, the capacity ratio is a ratio of the length of the first pipe 44 to the length of the second pipe 46. May be calculated based on Alternatively, the capacity ratio is based on the ratio of the passage sectional area of the first piping 44 and the passage sectional area of the second piping 46 when the length of the first piping 44 and the length of the second piping 46 are the same. May be calculated. The passage cross-sectional area is assumed to be constant except for the position where the flow rate adjusting valve is provided in the first pipe 44 and the second pipe 46.

  The predetermined value is set in advance as follows, for example. That is, the flow rate ratio between the first flow rate flowing through the first pipe 44 and the second flow rate flowing through the second pipe 46 is set from the capacity ratio. The flow rate is determined based on the passage cross-sectional area and the flow velocity. Therefore, when the passage cross-sectional area is the same between the first pipe 44 and the second pipe 46, the flow rate ratio is set from the flow rate ratio. The flow rate is determined based on the pressure in the pipe. Therefore, the pressure ratio is set as a predetermined ratio from the flow rate ratio. When the passage cross-sectional area differs between the first pipe 44 and the second pipe 46, the flow rate ratio is set from the flow rate ratio and the ratio of the passage cross-sectional area.

  The adjustment control using the flow rate adjustment valve 58 for controlling the pressure ratio is executed, for example, by a control process according to a flowchart based on FIG. In the flowchart shown in FIG. 6, the same step numbers are assigned to the same processes as those in FIG. Therefore, detailed description thereof will not be repeated.

  In S200, control device 100 calculates a pressure ratio between first pressure P1 and second pressure P2. In S202, control device 100 determines whether or not the calculated pressure ratio matches a predetermined ratio. For example, when the difference between the calculated pressure ratio and the predetermined ratio is equal to or less than the threshold value, control device 100 determines that the calculated pressure ratio matches the predetermined ratio. If it is determined that the calculated pressure ratio does not match the predetermined ratio (NO in S202), the process proceeds to S112.

  After the process of S112, the process proceeds to S204. In S204, control device 100 calculates a pressure ratio between first pressure P1 and second pressure P2. In S206, control device 100 determines whether or not the calculated pressure ratio matches a predetermined ratio. Since the determination method is as described above, detailed description thereof will not be repeated. If it is determined that the calculated pressure ratio matches the predetermined ratio (YES in S206), the process proceeds to S118.

  If it is determined in S202 that the calculated pressure ratio matches a predetermined ratio (YES in S202), the process proceeds to S120. If it is determined in S206 that the calculated pressure ratio does not match the predetermined ratio (NO in S206), the process proceeds to S112.

  In this way, the pressure ratio between the first pressure P1 and the second pressure P2 can be made to coincide with a predetermined ratio, so that a flow rate ratio corresponding to the pressure ratio is obtained, so that the inside of the first pipe 44 The period for sucking the urea water from the first injection valve 24 to the branch point 52 and the period for sucking the urea water in the second pipe 46 from the second injection valve 26 to the branch point 52 can be made the same. Therefore, urea water can be sucked back into the urea water tank 40 in parallel from each of the first injection valve 24 and the second injection valve 26. As a result, it is possible to suppress the urea water from remaining in the connection pipe 50. Thereby, freezing, deterioration, etc. of urea water in piping can be controlled.

  In the above-described embodiment, the urea water is sucked back when the IG off operation is performed. However, the embodiment is not particularly limited to when the engine is stopped by the IG off operation. The urea water may be sucked back when the engine is stopped without being turned off.

  In this way, it is possible to prevent the urea water from being deteriorated by the influence of heat from the exhaust pipe when the engine 10 is temporarily stopped.

  In the above-described embodiment, the flow rate adjustment valve 58 has been described as being provided on one of the first pipe 44 and the second pipe 46 with a small pressure loss. It may be provided in each of the second pipes 46.

  In this case, for example, even when the pressure loss is reversed due to temperature deviation or aging of the first pipe 44 and the second pipe 46, the urea water in the first pipe 44 is removed using the flow rate adjustment valve 58. The first period in which the first injection valve 24 sucks back to the branch point 52 and the second period in which the urea water in the second pipe 46 is sucked back from the second injection valve 26 to the branch point 52 can be the same period.

  In the above-described embodiment, the control device 100 adjusts the flow rate adjustment valve 58 based on the detection results of the first pressure sensor 54 and the second pressure sensor 56 during the reverse operation of the urea water pump 42 after the engine is stopped. As described above, the flow rate adjustment is performed based on the detection results of the first flow rate sensor that detects the flow rate of urea water in the first pipe 44 and the second flow rate sensor that detects the flow rate of urea water in the second pipe 46. The valve 58 may be controlled. For example, the control device 100 adjusts the flow rate adjustment valve 58 so that the flow rate difference or flow rate ratio between the first flow rate in the first pipe 44 and the second flow rate in the second pipe becomes a predetermined value. . The predetermined value is set based on the capacity ratio as described above.

  Even in this case, the urea water in the first pipe 44 is sucked back from the first injection valve 24 to the branch point 52 and the urea water in the second pipe 46 is sucked back from the second injection valve 26 to the branch point 52. The period can be the same.

  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. However, the first injection valve 24 and the second injection valve 26 are provided. 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, 54 1st Pressure sensor, 56 Second pressure sensor, 58 Flow rate adjustment valve, 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 provided in a portion of the exhaust pipe upstream of the exhaust purification catalyst and injecting urea water into the exhaust pipe by being switched from a valve closing state to a valve opening state during operation of the engine; Two injection valves;
A tank for storing the urea water;
A pipe having one end connected to the tank and the other end branched into two from a branch point in the middle and connected to each of the first injection valve and the second injection valve;
Provided in at least one of the first path from the branch point to the first injection valve and the second path from the branch point to the second injection valve in the pipe, A flow control valve capable of adjusting the cross-sectional area of the passage,
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;
After the engine is stopped, the first injection valve and the second injection valve are both opened, and the urea water in the first path and the second path is sucked back into the tank. A control device for controlling the pump,
The control device includes a first period from the start of operation of the pump until the urea water in the first path is sucked back to the branch point, and the second period after the operation of the pump is started. An exhaust treatment apparatus that adjusts the cross-sectional area of the passage using the flow rate adjustment valve so that a second period until the urea water in the path is sucked back to the branch point is the same. The exhaust treatment device includes:
A first pressure sensor provided on the first path for detecting a first pressure in the first path;
A second pressure sensor provided on the second path for detecting a second pressure in the second path;
The flow rate adjusting valve is provided between at least one of the first pressure sensor and the first injection valve and between the second pressure sensor and the second injection valve,
2. The control device according to claim 1, wherein the control device adjusts the passage cross-sectional area using the flow rate adjustment valve so that a difference or a ratio between the first pressure and the second pressure becomes a predetermined value. Exhaust treatment device. The exhaust treatment device includes:
A first flow rate sensor provided on the first path for detecting a first flow rate of the urea water in the first path;
A second flow rate sensor provided on the second route for detecting a second flow rate of the urea water in the second route;
The flow regulating valve is provided between at least one of the first flow sensor and the first injection valve and between the second flow sensor and the second injection valve,
2. The control device according to claim 1, wherein the controller adjusts the passage cross-sectional area using the flow rate adjustment valve so that a difference or ratio between the first flow rate and the second flow rate becomes a predetermined value. Exhaust treatment device.   The exhaust treatment device according to claim 2 or 3, wherein the predetermined value is set based on a capacity of the urea water in the first path and a capacity of the urea water in the second path. . 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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