JP6663680B2 - Control device for reducing agent injection device - Google Patents

Description

  The present invention relates to a control device of a reducing agent injection device for controlling a reducing agent injection device that supplies a reducing agent to an exhaust passage of an internal combustion engine.

The exhaust gas of an internal combustion engine such as a diesel engine mounted on a vehicle contains NO _x (nitrogen oxide). As an apparatus for purifying exhaust by decomposing the reduced to nitrogen and water or the like such NO _X, urea SCR (Selective Catalystic Reduction) system has been put into practical use. The urea SCR system is a system that decomposes NO _X by reacting NO _X in exhaust gas with ammonia using an aqueous urea solution as a reducing agent.

Such a urea SCR system includes a selective reduction catalyst disposed in an exhaust passage, and a reducing agent injection device for supplying a urea aqueous solution to an exhaust passage upstream of the selective reduction catalyst. Selective reduction catalyst has the function of promoting the reduction reaction of the NO _X and ammonia in the exhaust adsorbs ammonia urea solution is generated by decomposition, it flows. Further, the reducing agent injection device includes a pump for pumping the urea aqueous solution contained in the storage tank, an injection valve for injecting the urea aqueous solution pumped by the pump, and a control device for controlling the pump and the injection valve. .

  The urea aqueous solution used in the urea SCR system has a different freezing temperature depending on the concentration. Even at the lowest freezing temperature, the temperature is on the order of minus 11 ° C. Therefore, when the internal combustion engine is stopped, the urea aqueous solution is discharged from the reducing agent injection device so that the pump, the injection valve, the piping for flowing the urea aqueous solution, and the like are not damaged by the urea aqueous solution being frozen and the volume expanding while the vehicle is stopped. Collected in storage tank. The recovered aqueous urea solution is refilled into the reducing agent injection device when the reducing agent injection device is started.

  On the other hand, when the injection valve is exposed to a high temperature, the solvent of the urea aqueous solution adhering to the injection valve evaporates, the concentration increases, and the freezing temperature increases, so that the urea aqueous solution may crystallize. For example, if the function of the cooling means of the injection valve stops when the internal combustion engine is stopped, the urea aqueous solution attached to the injection valve may be heated and crystallized under the influence of the residual exhaust heat. Further, even when the internal combustion engine is operating, if the injection of the aqueous urea solution is not performed for a long time, the aqueous urea solution attached to the injection valve may be heated by the exhaust heat and crystallized. When the urea aqueous solution is crystallized, the valve body of the injection valve may stick, causing an open or fixed state in which the injection hole is not closed while being opened, or a closed and fixed state in which the injection hole is kept closed.

  Furthermore, fine particles such as soot contained in the exhaust gas may enter the injection valve through the injection hole and adhere to a sliding portion or a seating portion of the valve body, so that the above-described open fixation and close fixation may occur. is there.

  Here, when the sticking of the injection valve occurs, a measure to be taken differs depending on whether the sticking is an open sticking or a closed sticking. For example, when the injection valve is closed and fixed, the urea aqueous solution does not leak into the exhaust pipe even if the operation of the pump is maintained, but when the injection valve is open and fixed, If the driving is maintained, the urea aqueous solution is dripped off, and thus it is necessary to stop the driving of the pump.

  Patent Literature 1 proposes a reducing agent injection valve abnormality determination device that can accurately determine whether the injection valve is open or closed when the valve body of the injection valve malfunctions. ing. Specifically, based on a pressure change in the reducing agent passage when the pressure in the reducing agent passage for supplying the urea aqueous solution to the injection valve is reduced, the operation failure of the valve body is caused by the open fixation or the close fixation. There is disclosed an abnormality determination device for determining whether an object is an object.

JP 2012-102637 A

  The abnormality determination device disclosed in Patent Literature 1 can execute the determination of the sticking of the open or closed state only while the injection control of the urea aqueous solution by the reducing agent injection device is stopped, such as when the internal combustion engine is stopped. it can. That is, the abnormality determination device disclosed in Patent Literature 1 cannot perform the determination of the open sticking or the closed sticking during the injection control of the urea aqueous solution. If so, injection control must be prohibited. If the open / closed state of the injection valve can be determined even during the injection control of the urea aqueous solution, the injection control can be continued if there is no problem in the injection control of the urea aqueous solution by the injection valve. It is considered to be.

  Also, while the injection control of the urea aqueous solution is stopped, even if the injection valve is stuck, if the adhesion is due to crystallization of the urea aqueous solution, the crystallized urea aqueous solution is immersed in the liquid urea aqueous solution. As a result, liquefaction may occur again, and the malfunction of the valve body may be improved. That is, when the injection valve is fixed before the start of the injection control, it may be possible to try to melt the crystallized urea aqueous solution. However, even when an attempt is made to melt the crystallized aqueous urea solution, if the melting is not sufficient, the injection valve may be determined to be abnormal after the start of the injection control of the aqueous urea solution. In this case, when the injection valve is in the closed and fixed state, the urea aqueous solution does not fall down even if the operation of the pump is maintained, so that the crystallized urea aqueous solution is again melted before the injection control is prohibited. be able to. Therefore, in order to improve the state in which the crystallized urea aqueous solution is insufficiently melted, it is desirable to be able to determine whether the injection valve is open or closed during injection control of the urea aqueous solution.

  The present invention has been made in view of the above-described problems, and it is an object of the present invention to determine whether an abnormality that occurs in an injection valve during opening control of a reducing agent is open sticking or closed sticking. It is an object of the present invention to provide a control device for a reducing agent injection device, which can determine whether the reducing agent is ejected.

In order to solve the above problems, according to an aspect of the present invention, an injection valve attached to an exhaust pipe of an internal combustion engine causes an exhaust gas of the internal combustion engine to be provided upstream of a reduction catalyst disposed in an exhaust passage. a control apparatus for controlling the reducing agent injection device for injecting a reducing agent for purifying NO _X, the pump for pumping the reducing agent so that the pressure of the reducing agent supplied to the injection valve becomes a predetermined target value An injection control unit that controls the valve opening operation of the injection valve while controlling the output of the injection valve, based on the current waveform supplied to the injection valve and the output of the pump during execution of the injection control of the reducing agent. A control unit for the reducing agent injection device, comprising: an abnormality determination unit that determines whether the injection valve is abnormal while distinguishing between the open and closed states.

  The abnormality determining unit determines that the injection valve is in the open and fixed state when the change point does not appear in the current waveform and the output of the pump is maintained within the first range, and the change point in the current waveform. Does not appear, and the output of the pump is maintained within a second range that is smaller than the first range, it may be determined that the injection valve is in the closed and fixed state.

  The abnormality determination unit may stop the control of the injection of the reducing agent when determining that the injection valve is in the open and fixed state.

  When the abnormality determination unit determines that the injection valve is in the closed and fixed state, a recovery control unit that once recovers the reducing agent supplied to the injection valve and then resupplies the injection agent to the injection valve may be provided.

  The abnormality determination unit may prohibit the execution of the injection control of the injection valve when the number of times that the injection valve is determined to be in the closed and fixed state is equal to or more than a predetermined threshold.

  At the time of starting the reducing agent injection device and at the time of re-supply of the reducing agent by the return control unit, the output of the pump that pumps the reducing agent while the pressure of the reducing agent supplied to the injection valve is increased is fixed, and the injection valve is operated. A pressure judging unit for judging the presence or absence of clogging of the injection valve based on the pressure of the reducing agent when the valve is maintained in the open state is provided.If the pressure judging unit judges that there is no abnormality, the injection control unit May be started, and the abnormality determination unit may determine the abnormality of the injection valve.

  When the pressure determination unit determines that there is an abnormality, a recovery control unit may be provided that once recovers the reducing agent supplied to the injection valve and then resupplies the reducing agent to the injection valve.

  The pressure determination unit may prohibit the execution of the injection control of the injection valve when the number of times of determining that there is an abnormality is equal to or greater than a predetermined threshold.

  As described above, according to the present invention, during the control of the injection of the reducing agent, it is possible to determine whether the abnormality that has occurred in the injection valve is open sticking or closed sticking.

It is a schematic diagram showing a urea SCR system provided with a reducing agent injection device concerning an embodiment of the invention. It is a block diagram showing an example of composition of a control device of a reducing agent injection device concerning the embodiment. It is explanatory drawing which shows the state in each control mode of the reducing agent injection device concerning the embodiment. FIG. 5 is a diagram for explaining clogging determination of an injection valve based on pressure. FIG. 5 is a diagram for explaining abnormality determination of an injection valve based on a current waveform. FIG. 4 is a diagram for explaining abnormality determination of an injection valve based on a pump output. It is a flow chart which shows processing by the control device of the reducing agent injection device concerning the embodiment.

  Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. In the specification and the drawings, components having substantially the same functional configuration are denoted by the same reference numerals, and redundant description is omitted.

<1. Overall configuration of urea SCR system>
First, an example of the overall configuration of the urea SCR system 10 including the reducing agent injection device 20 will be described. FIG. 1 is an explanatory diagram illustrating a schematic configuration of the urea SCR system 10. The urea SCR system 10 includes a reduction catalyst 13 provided in the middle of an exhaust pipe 11 connected to an exhaust system of an internal combustion engine 5 typified by a diesel engine or the like, and an exhaust passage upstream of the reduction catalyst 13 in an exhaust passage. A reducing agent injection device 20 for injecting the reducing agent. The urea SCR system 10 is mounted on a vehicle, a construction machine, an agricultural machine, or the like, and purifies exhaust gas by reducing and decomposing NO _X in exhaust gas discharged from the internal combustion engine 5 using a urea aqueous solution as a reducing agent. System.

  The aqueous urea solution may be, for example, an aqueous urea solution having a lowest freezing temperature and a concentration of about 32.5%. The freezing temperature in this case is about -11 ° C. Such an aqueous urea solution has a property that the freezing temperature increases as the concentration increases, and the urea solution is easily crystallized by evaporating water as a solvent.

The reduction catalyst 13 selectively reduces NO _X contained in the exhaust gas of the internal combustion engine 5 using an aqueous urea solution. In the present embodiment, the ammonia generated by the decomposition of the urea aqueous solution injected by the reducing agent injection device 20 is adsorbed on the reduction catalyst 13, and the NO _X in the exhaust gas flowing into the reduction catalyst 13 reacts with the ammonia. Be reduced. The reduction catalyst 13 has such a characteristic that the higher the catalyst temperature, the smaller the amount of adsorbable ammonia. Further, the reduction catalyst 13 has such a characteristic that the higher the actual adsorption rate of ammonia with respect to the adsorbable amount, the higher the NO _X reduction efficiency.

The reducing agent injection device 20 injects a urea aqueous solution as a reducing agent into an exhaust passage upstream of the reduction catalyst 13. Injection amount of the urea aqueous solution, and the concentration of NO _X contained in the exhaust, the ammonia adsorption capacity of the reduction catalyst 13, based on the temperature of the reduction catalyst 13, is NO _X or ammonia to the downstream side of the reduction catalyst 13 It is controlled not to flow out.

A temperature sensor 15 for detecting the exhaust gas temperature Tgas is attached to the exhaust pipe 11 upstream of the reduction catalyst 13. The exhaust gas temperature Tgas detected by the temperature sensor 15 is also used for estimating the temperature of the reduction catalyst 13. In addition to this, the exhaust pipe 11, NO _X concentration sensor and the ammonia sensor or the like may be provided (not shown).

<2. Reducing agent injection device>
Next, an example of the configuration of the reducing agent injection device 20 will be described in detail. As shown in FIG. 1, the reducing agent injection device 20 includes an injection valve 31 fixed to the exhaust pipe 11 on the upstream side of the reduction catalyst 13, and a pump unit 40 having a pump 41 for pumping the urea aqueous solution. The drive of the pump 41 and the injection valve 31 is controlled by the control device 100. The control device 100 is capable of acquiring information on the operating state of the internal combustion engine 5, such as the fuel injection amount, the injection timing, and the engine speed, from the control device 70 of the internal combustion engine 5.

  The storage tank 50 and the pump 41 are connected by a first reducing agent passage 58, and the pump 41 and the injection valve 31 are connected by a second reducing agent passage 57. A return passage 59 whose other end is connected to the storage tank 50 is connected to the second reducing agent passage 57, and the return passage 59 is provided with the orifice 45. The orifice 45 is provided so that the pressure in the second reducing agent passage 57 is easily maintained. Further, the second reducing agent passage 57 is provided with a pressure sensor 43 for detecting the pressure in the second reducing agent passage 57 that indicates the pressure Pu of the aqueous urea solution supplied to the injection valve 31. .

  As the injection valve 31, for example, an electromagnetic injection valve that is switched between valve opening and valve closing by energization control is used. The injection valve 31 includes a coil, and has a structure in which the valve element moves and opens by a magnetic force generated by energizing the coil. In the present embodiment, since the pressure Pu of the aqueous urea solution supplied to the injection valve 31 is controlled to be the predetermined target value Ptgt, the control device 100 sets the valve opening time according to the target injection amount of the aqueous urea solution. Adjust. The injection valve 31 is for directly injecting the urea aqueous solution into the exhaust pipe 11, and is attached to the exhaust pipe 11 so that the injection hole faces the inside of the exhaust pipe 11.

  The injection valve 31 is held in a cooling cover, and the cooling water of the internal combustion engine 5 can flow through the cooling cover. The passage of the cooling water in the cooling cover forms a part of the cooling water circulation passage 87. The cooling water circulation passage 87 branches from the cooling passage 86 of the cooling device 60 provided in the internal combustion engine 5, and joins the cooling passage 86 of the internal combustion engine 5 again via the cooling cover of the injection valve 31. After the start of the internal combustion engine 5, the cooling water always flows through the cooling water circulation passage 87. Therefore, during the operation of the internal combustion engine 5, in a situation where the injection valve 31 can be heated by high-temperature exhaust heat or the like, cooling water flows through the cooling water circulation passage 87, and overheating of the injection valve 31 is suppressed.

  The pump 41 is composed of, for example, an electric diaphragm pump or a motor pump. The output of the pump 41 is controlled based on a control signal output from the control device 100. In the present embodiment, the control device 100 determines the deviation ΔP between the pressure Pu detected by the pressure sensor 43 and the target value Ptgt so that the pressure Pu supplied to the injection valve 31 is maintained at the predetermined target value Ptgt. Based on this, the output of the pump 41 is feedback-controlled.

  The pump unit 40 is provided with a flow path switching valve 71 for switching the direction in which the aqueous urea solution pumped by the pump 41 flows. The flow path switching valve 71 is configured by, for example, an electromagnetic switching valve, and is driven by the control device 100. In the present embodiment, the flow path switching valve 71 is configured to connect the suction side of the pump 41 to the first reducing agent passage 58 and the discharge side of the pump 41 to the second reducing agent passage 57, respectively. And the second state in which the discharge side of the pump 41 and the first reducing agent passage 58 and the suction side of the pump 41 and the second reducing agent passage 57 are connected.

  When controlling the injection of the aqueous urea solution into the exhaust pipe 11, the flow path switching valve 71 is operated so that the aqueous urea solution flows from the storage tank 50 to the injection valve 31. When the aqueous urea solution in the reducing agent injection device 20 is collected in the storage tank 50, the flow path switching valve 71 is operated so that the aqueous urea solution flows from the injection valve 31 side to the storage tank 50 side. Note that, instead of using the flow path switching valve 71, a urea aqueous solution may be recovered by using a pump that can rotate in the reverse direction.

  The coolant of the internal combustion engine 5 circulates through the reducing agent injection device 20. The cooling water circulation passage 85 branched from the cooling device 60 of the internal combustion engine 5 is provided with a cooling water circulation passage 87 passing through the cooling cover of the injection valve 31 and a cooling water circulation passage 89 passing through the storage tank 50 and the pump unit 40 on the way. Branch. Among these, an on-off valve 81 driven by the control device 100 is provided in the cooling water circulation passage 89, so that the flow and shutoff of the cooling water can be switched. During operation of the internal combustion engine 5, cooling water always flows through the cooling water circulation passage 87 to cool the injection valve 31. On the other hand, the cooling water flowing through the cooling water circulation passage 89 is used as a heating medium, and when the storage tank 50 and the pump unit 40 need to be heated, the on-off valve 81 is opened and the cooling water flows.

<3. Control device>
Next, a configuration example of the control device 100 used for controlling the reducing agent injection device 20 according to the present embodiment will be described. The control device 100 is configured to include a known microcomputer, a pump 41, an injection valve 31, a drive circuit for the flow path switching valve 71, and the like. FIG. 2 is a block diagram functionally showing the configuration of control device 100. FIG. 3 shows the flow of the pump 41 and the flow of the urea aqueous solution when the pressure determination unit 105 performs the clogging determination, when the injection control unit 101 performs the urea aqueous solution injection control, and when the return control unit 107 performs the return control. , And the control state of the injection valve 31.

  The control device 100 includes an injection control unit 101, an abnormality determination unit 103, a pressure determination unit 105, and a return control unit 107. Each of these units may be specifically realized by executing a program by a microcomputer. The detection signals of the pressure sensor 43 and the temperature sensor 15 and information related to the operation state of the internal combustion engine 5 and the like are input to the control device 100 directly or via a bus line such as a CAN. Further, the control device 100 includes a storage element (not shown) such as a RAM (Random Access Memory) and a ROM (Read Only Memory). These storage elements store programs executed by the microcomputer, various parameters used in arithmetic processing, arithmetic results, detection results, and the like.

(3-1. Injection control unit)
Injection control unit 101, in order to purify the NO _X contained in exhaust gas of the internal combustion engine 5, to perform the injection control for injecting the urea solution into the exhaust pipe 11. In the present embodiment, the injection control unit 101 starts the injection control of the aqueous urea solution when the pressure determination unit 105 described later determines that there is no abnormality in the injection valve 31. The injection control unit 101 executes output control of the pump 41 and energization control of the injection valve 31. The injection control unit 101 reads the detection signal of the pressure sensor 43, and performs feedback control of the output of the pump 41 so that the pressure Pu of the urea aqueous solution supplied to the injection valve 31 becomes a predetermined target value Ptgt. Further, the injection control unit 101 calculates the target injection amount of the urea aqueous solution and controls the valve opening time of the injection valve 31 based on the calculated target injection amount.

  As shown in FIG. 3, during execution of the injection control, the output of the pump 41 is feedback-controlled based on the pressure Pu of the urea aqueous solution. The flow path switching valve 71 is held so that the urea aqueous solution flows from the storage tank 50 toward the injection valve 31 (forward direction). In addition, the energization time of the injection valve 31 is controlled so that the valve opening time of the injection valve 31 is adjusted based on the target injection amount. In the present embodiment, the injection control unit 101 controls a duty ratio, which is a ratio of a valve opening time during a predetermined injection cycle, based on a target injection amount.

For example, the injection control unit 101 obtains the amount of ammonia required to reduce the NO _X based on the amount of NO _{X in} the exhaust gas of the internal combustion engine 5, and also determines the amount of ammonia that is adsorbed by the reduction catalyst 13 on the target amount of ammonia. Insufficient amounts of ammonia are determined, and the amount of the urea aqueous solution corresponding to the sum of these amounts can be used as the target injection amount. The amount of NO _X in the exhaust gas, NO _X concentrations are estimated based on the operating state of the internal combustion engine 5 or, the NO _X concentration detected by the NO _X sensor, using _the amount of NO _X obtained by multiplying the exhaust gas flow rate be able to. Then, the injection control unit 101 obtains an ammonia amount corresponding to the calculated NO _X amount.

Further, as the target adsorption amount of ammonia in the reduction catalyst 13, a value obtained by multiplying an adsorbable amount corresponding to the catalyst temperature estimated based on the exhaust gas temperature Tgas by a target adsorption rate can be used. The target adsorption rate may be, for example, 70 to 80%. By the target adsorption rate and 70-80%, is maintained adsorption rate is relatively high, while the reduction efficiency of the NO _X increases, even when the catalyst temperature is rapidly increased, ammonia can adsorb The amount can be kept below the current adsorption amount of ammonia. Then, the injection control unit 101 obtains an excess or deficiency ammonia amount from a difference between the current ammonia adsorption amount obtained by the integration and the target adsorption amount.

Then, the injection control unit 101 adds the excess / deficiency ammonia amount with respect to the target adsorption amount of the reduction catalyst 13 and the previously obtained ammonia amount, and calculates the amount of the urea aqueous solution corresponding to the calculated ammonia amount as the target injection amount. The drive of the injection valve 31 is controlled. As described above, since the pressure of the urea aqueous solution supplied to the injection valve 31 is controlled to be kept constant, the injection control unit 101 adjusts the injection time according to the target injection amount. By executing such a injection control of the urea aqueous solution, reducing the outflow of ammonia to the downstream side while being suppressed in the catalyst 13, the adsorption rate of ammonia in the reduction catalyst 13 is maintained high, improving the reduction efficiency of the NO _X Can be done.

(3-2. Return control unit)
The return control unit 107 controls the supply of the aqueous urea solution to the injection valve 31 again after the aqueous urea solution supplied to the injection valve 31 is once collected in the storage tank 50 (hereinafter, such control is also referred to as “return control”). )I do. In the present embodiment, when the abnormality determining unit 103 described later determines that the injection valve 31 is in the closed and fixed state, and when the pressure determining unit 105 described later determines that the injection valve 31 is abnormal, the return is performed. Execute control.

  Specifically, the return control unit 107 switches the flow path so that the urea aqueous solution flows from the injection valve 31 side to the storage tank 50 side by energizing the flow path switching valve 71, and sets the pump for a predetermined time period. 41 is driven. At this time, the return control unit 107 may energize the injection valve 31 and output a valve opening instruction to the injection valve 31. Thereby, the aqueous urea solution in the reducing agent injection device 20 is sucked back by the pump 41 and collected in the storage tank 50. Thereafter, the return control unit 107 stops the energization of the flow path switching valve 71, switches the flow path so that the aqueous urea solution flows from the storage tank 50 side to the injection valve 31, and drives the pump 41. Thereby, the urea aqueous solution is refilled in the reducing agent injection device 20.

  As shown in FIG. 3, during execution of the return control, the output of the pump 41 is kept constant. When recovering the aqueous urea solution, the flow path switching valve 71 is switched so that the aqueous urea solution flows from the injection valve 31 toward the storage tank 50 (in the opposite direction). Thereafter, when refilling the urea aqueous solution, the flow path switching valve 71 is switched so that the urea aqueous solution flows from the storage tank 50 side toward the injection valve 31 side (forward direction). When the urea aqueous solution is collected, a valve opening instruction is output to the injection valve 31, and when the urea aqueous solution is refilled, the injection valve 31 is kept closed.

  The recovery and refilling of the urea aqueous solution is performed by the return control unit 107. For example, when the urea aqueous solution is crystallized in the injection valve 31, the liquid urea aqueous solution reaches the injection valve 31 and is crystallized. There is a possibility that the converted aqueous urea solution may be melted. For example, when the urea aqueous solution is recovered, the urea aqueous solution may remain on the second reducing agent passage 57 in a region close to the injection valve 31 in some cases. In such a case, when the urea aqueous solution is refilled next time, the remaining urea aqueous solution may be pushed into the injection valve 31 side and may reach the urea aqueous solution crystallized in the injection valve 31. As a result, the crystallized aqueous urea solution is melted, and the injection control of the aqueous urea solution can be returned to a state in which the injection control of the aqueous urea solution can be executed without inhibiting the injection control of the aqueous urea solution.

(3-3. Pressure determination unit)
The pressure determination unit 105 determines whether the injection valve 31 is clogged based on the pressure of the aqueous urea solution detected by the pressure sensor 43 when the reducing agent injection device 20 is started and when the return control unit 107 refills the aqueous urea solution. Determine the presence or absence. Specifically, when the pressure Pu of the aqueous urea solution supplied to the injection valve 31 is increased to a predetermined value or more, the pressure determination unit 105 keeps the output of the pump 41 constant and maintains the injection valve 31 in the open state. I do. As shown in FIG. 3, the output of the pump 41 is kept constant during the execution of the clogging determination. The flow path switching valve 71 is held so that the urea aqueous solution flows from the storage tank 50 toward the injection valve 31 (forward direction). Further, a full open instruction is output to the injection valve 31.

  At this time, the pressure change of the aqueous urea solution may differ between the case where the injection valve 31 is normally opened and the case where the injection valve 31 is clogged. FIG. 4 is an explanatory diagram showing a change in the pressure of the urea aqueous solution when the injection valve 31 is maintained in the open state with the output of the pump 41 kept constant. FIG. 4 shows an example in which an injection valve 31 having three injection holes is used. When the injection valve 31 is normally opened, that is, when the aqueous urea solution is jetted from all three injection holes, the pressure Pu of the aqueous urea solution decreases at a predetermined speed (line A). On the other hand, when the injection valve 31 does not open, that is, when the urea aqueous solution is not ejected from all three injection holes, the pressure Pu of the urea aqueous solution does not change (line D). Even when the injection hole is not clogged and the injection valve 31 is in the closed and fixed state, the pressure Pu of the urea aqueous solution does not change (line D).

  In addition, even when the injection valve 31 is opened, when a part of the injection hole is clogged, the decreasing speed of the pressure Pu of the aqueous urea solution becomes smaller than in a normal state. For example, when one injection hole is clogged and the urea aqueous solution is ejected from the two injection holes, the decreasing speed of the pressure Pu of the urea aqueous solution is slightly smaller than that in the normal case (line B). When the two injection holes are clogged and the urea aqueous solution is jetted from one injection hole, the decreasing speed of the pressure Pu of the urea aqueous solution further decreases (line C).

  Therefore, for example, as the pressure threshold after a predetermined time has elapsed after the injection valve 31 is opened, a plurality of thresholds capable of distinguishing each pressure change mode are set according to the output of the pump 41 to be fixed. By doing so, it is possible to determine whether the injection valve 31 is clogged. At this time, a plurality of threshold values may be set so that the degree of clogging of the injection holes can be distinguished, or one threshold value can be set so that only the presence or absence of clogging of the injection holes can be determined.

  In the present embodiment, when it is determined that the injection valve 31 is abnormal, the pressure determination unit 105 causes the return control unit 107 to execute the return control. At this time, the pressure determination unit 105 counts up the first counter value, and when the first counter value reaches the predetermined threshold value Th1, considers that the abnormality of the injection valve 31 is not solved and injects the urea aqueous solution. Prohibit control.

  The determination of clogging by the pressure determination unit 105 can be performed relatively easily as compared with the abnormality determination by the abnormality determination unit 103 described later. Therefore, when it is determined in the clogging determination by the pressure determination unit 105 that there is an abnormality, the injection control of the urea aqueous solution can be stopped at least until the clogging is eliminated. On the other hand, in the clogging determination by the pressure determination unit 105, it is conceivable that it is determined that there is no abnormality even when the injection valve 31 is in the open fixed state. For this reason, the control device 100 according to the present embodiment executes the abnormality determination by the abnormality determination unit 103 separately from the clogging determination by the pressure determination unit 105.

(3-4. Abnormality determination unit)
The abnormality determination unit 103 determines that the injection valve 31 has no abnormality by the pressure determination unit 105, and based on the current waveform supplied to the injection valve 31 and the output of the pump 41 in a state where the injection control of the urea aqueous solution is started. Thus, the abnormality of the injection valve 31 is determined. Specifically, the abnormality determination unit 103 monitors the current waveform supplied to the injection valve 31 and the output of the pump 41 while the injection control of the urea aqueous solution is being executed, and moves the valve body based on the current waveform. By determining whether or not the valve body is fixed, it is determined whether or not the valve body is fixed. Further, when the valve body is stuck, the abnormality determination unit 103 determines whether the stuck state is the open stuck state or the closed stuck state based on the output of the pump 41.

  FIG. 5 is an explanatory diagram showing a difference in a current waveform supplied to the injection valve 31 depending on whether or not the valve body is fixed. The injection valve 31 has a configuration in which the magnetic force for attracting the valve increases as the amount of current supplied to the electromagnetic coil increases, and the valve moves. When the valve body is not fixed (solid line), if the amount of energization is gradually increased, the current value once drops when the valve body starts to move, so that a change point appears in the current waveform. On the other hand, when the valve element is stuck (broken line), the change point does not appear in the current waveform because the valve element does not move even if the amount of current is increased.

  The abnormality determination unit 103 determines whether or not such a change point has occurred in the current waveform supplied to the injection valve 31 during execution of the injection control, thereby determining whether or not the valve element is stuck. Can be determined. When a change point appears in the current waveform, that is, when the valve body is not fixed, the urea aqueous solution is injected by the injection valve 31 together with the result of no abnormality in the clogging determination already performed by the pressure determination unit 105. It can be determined that the injection control can be performed normally. Therefore, the abnormality determination unit 103 determines that there is no abnormality in the injection valve 31 and continues the injection control of the urea aqueous solution.

  On the other hand, when a change point does not appear in the waveform of the current supplied to the injection valve 31, that is, when the valve element is fixed, a difference occurs in the output of the pump 41 depending on whether the fixing is open or closed. FIG. 6 is an explanatory diagram illustrating the output of the pump 41 when the injection valve 31 is in the open fixed state and the closed fixed state. During the injection control of the urea aqueous solution, the output of the pump 41 is controlled such that the pressure Pu of the urea aqueous solution supplied to the injection valve 31 is maintained at the target value Ptgt. In other words, the injection amount (including zero) of the urea aqueous solution is constant, and the output of the pump 41 is substantially constant.

  However, when the injection valve 31 is closed and fixed, the urea aqueous solution is not injected, while when the injection valve 31 is open and fixed, the urea aqueous solution is injected. Therefore, the output of the pump 41 for maintaining the pressure Pu of the aqueous urea solution at the target value Ptgt is larger when the injection valve 31 is in the open fixed state than in the closed and fixed state. Therefore, the abnormality determination unit 103 determines the fixed state of the injection valve 31 by comparing the actual output of the pump 41 with a threshold, a range, or the like that can distinguish the open fixed state or the closed fixed state of the injection valve 31. I do.

  When the injection valve 31 is in the open and fixed state, the urea aqueous solution is always injected into the exhaust pipe 11 while the urea aqueous solution is supplied to the injection valve 31. As a result, the urea aqueous solution adheres to the exhaust pipe 11 and the crystallization proceeds due to heating, and the generated ammonia flows out to the downstream side of the reduction catalyst 13 without being completely adsorbed by the reduction catalyst 13. There is a possibility that. Therefore, when the injection valve 31 is in the open and fixed state, the abnormality determination unit 103 prohibits the injection control of the urea aqueous solution. Along with this, the abnormality determination unit 103 may collect the urea aqueous solution in the reducing agent injection device 20 into the storage tank 50 or display a warning to a driver or the like.

  On the other hand, when the injection valve 31 is in the closed and fixed state, the urea aqueous solution does not leak into the exhaust pipe 11 even if the urea aqueous solution is supplied to the injection valve 31. Therefore, when the injection valve 31 is in the closed and fixed state, the abnormality determination unit 103 causes the return control unit 107 to execute the return control, and attempts to eliminate the sticking of the valve body by melting the crystallized urea aqueous solution. At this time, the abnormality determination unit 103 counts up the second counter value, and when the second counter value reaches a predetermined threshold value Th2, considers that the closed and fixed state of the injection valve 31 is not eliminated, and Injection control is prohibited.

  The abnormality determination of the injection valve 31 by the abnormality determination unit 103 can be performed during the injection control of the urea aqueous solution. Therefore, when there is no abnormality in the injection valve 31, the abnormality determination of the injection valve 31 can be completed without affecting the injection control of the urea aqueous solution. In addition, since the abnormality determination of the injection valve 31 can determine the open fixed state and the closed fixed state of the injection valve 31, in the case of the closed fixed state, the valve body is set before the injection control is prohibited. Can be eliminated. Therefore, when the crystallized aqueous urea solution can be melted, the injection control of the aqueous urea solution can be continued.

<4. Flow chart>
Next, an example of a control method of the reducing agent injection device executed by the control device 100 according to the present embodiment will be described with reference to FIG.

  First, in step S10, when the ignition switch of the internal combustion engine 5 is turned on to start the reducing agent injection device 20, the values of the first counter and the second counter are reset in step S14.

  Next, in Step S18, the pressure determination unit 105 of the control device 100 determines whether the injection valve 31 is clogged based on the pressure Pu of the urea aqueous solution supplied to the injection valve 31. For example, in a state where the urea aqueous solution in the storage tank 50 is pumped toward the injection valve 31 by the pump 41 and the pressure Pu detected by the pressure sensor 43 has reached the target value Ptgt, the pressure determination unit 105 The output is kept constant, and the injection valve 31 is maintained in the open state. Then, the pressure determination unit 105 obtains the value of the pressure Pu at a point in time when a predetermined time has elapsed since the injection valve 31 was opened, and determines whether the injection valve 31 is clogged. Instead of the value of the pressure Pu at a certain point in time, the clogging of the injection valve 31 may be determined using the pressure drop speed after the injection valve 31 is opened.

  Next, in step S22, the pressure determination unit 105 determines whether there is an abnormality in the injection valve 31 as a result of the clogging determination. When there is an abnormality in the injection valve 31 (S22: Yes), the pressure determination unit 105 causes the return control unit 107 to execute the return control in step S26. For example, the return control unit 107 energizes the flow path switching valve 71 so that the urea aqueous solution pumped by the pump 41 flows from the injection valve 31 side to the storage tank 50 side, and then drives the pump 41 for a predetermined time. . Thereby, the aqueous urea solution in the reducing agent injection device 20 is sucked back into the storage tank 50. At this time, a valve opening instruction may be output to the injection valve 31. When a part of the injection hole is clogged, the urea aqueous solution can be efficiently sucked back when the injection valve 31 is opened.

  After the return of the urea aqueous solution is completed, the return control unit 107 stops supplying power to the flow path switching valve 71, and the urea aqueous solution pumped by the pump 41 is moved from the storage tank 50 side to the injection valve 31 side. And the pump 41 is driven. Thereby, the urea aqueous solution is refilled in the reducing agent injection device 20. As a result of the return control, when the aqueous urea solution reaches the aqueous urea solution crystallized in the injection valve 31, the crystallized aqueous urea solution is melted, and the abnormality of the injection valve 31 can be eliminated.

  After the return control by the return control unit 107 ends, in step S30, the pressure determination unit 105 determines whether or not the first counter value is equal to or greater than a preset threshold Th1. When the first counter value is less than the threshold value Th1 (S30: No), the pressure determination unit 105 counts up the first counter value in step S34 because there is room for eliminating the clogging of the injection valve 31. Returning to step S18, the clogging determination is repeated. On the other hand, when the first counter value is equal to or greater than the threshold Th1 (S30: Yes), the clogging of the injection valve 31 is not eliminated even though the return control is performed a predetermined number of times, and the injection control of the urea aqueous solution is executed. Can be considered difficult. Therefore, the pressure determination unit 105 proceeds to step S38 and makes an error determination. In this case, the injection control of the urea aqueous solution is not executed. The pressure determination unit 105 may activate a warning device to notify a driver or the like of an abnormality of the injection valve 31.

  On the other hand, as a result of the clogging determination in step S22 described above, if there is no abnormality in the injection valve 31 (S22: No), in step S42, the injection control unit 101 starts injection control of the urea aqueous solution. For example, the injection control unit 101 performs feedback control of the output of the pump 41 so that the pressure Pu of the aqueous urea solution supplied to the injection valve 31 becomes the target value Ptgt. Further, the injection control unit 101 sets the valve opening time of the injection valve 31 based on the target injection amount of the urea aqueous solution, and controls the energization of the injection valve 31.

  After the injection control of the aqueous urea solution is started, in step S <b> 46, the abnormality determination unit 103 performs the abnormality determination of the injection valve 31 based on the current waveform supplied to the injection valve 31 and the output of the pump 41. Specifically, the abnormality determination unit 103 detects the value of the current supplied to the injection valve 31 and the output of the pump 41 every predetermined cycle. Further, the abnormality determination unit 103 determines whether the valve body is fixed based on the presence or absence of a predetermined change point in the detected current waveform of the injection valve 31. Further, when the valve body is stuck, the abnormality determination unit 103 compares the output of the pump 41 with a preset threshold or range to determine whether the injection valve 31 is stuck open or closed. I do.

  Next, in step S50, the abnormality determination unit 103 determines whether there is an abnormality in the injection valve 31 as a result of the abnormality determination of the injection valve 31. If there is no abnormality in the injection valve 31 (S50: No), it can be considered that the reducing agent injection device 20 can normally execute the injection control, and therefore, the abnormality determination unit 103 proceeds to step S70, and the injection control unit 101 Then, the injection control of the urea aqueous solution is continued. On the other hand, when there is an abnormality in the injection valve 31 (S50: Yes), in step S54, the abnormality determination unit 103 determines whether the abnormality of the injection valve 31 is due to the close-stuck.

  When the injection valve 31 is in the open and fixed state (S54: No), if the driving of the pump 41 is continued, the urea aqueous solution is dripped into the exhaust pipe 11, so the abnormality determination unit 103 proceeds to step S38. After the error is determined, the injection control of the aqueous urea solution is immediately stopped. The abnormality determination unit 103 may activate a warning device to notify a driver or the like of an abnormality of the injection valve 31. On the other hand, when the injection valve 31 is in the closed and fixed state (S54: Yes), in step S58, the abnormality determination unit 103 determines whether the second counter value is less than a preset threshold Th2.

  When the second counter value is equal to or greater than the threshold value Th2 (S58: No), the closed and fixed state of the injection valve 31 is not eliminated even though the return control is performed a predetermined number of times, and the injection control of the urea aqueous solution is executed. Can be considered difficult. Therefore, the abnormality determination unit 103 proceeds to step S38, makes an error determination, and stops the injection control of the aqueous urea solution. The abnormality determination unit 103 may activate a warning device to notify a driver or the like of an abnormality of the injection valve 31. On the other hand, when the second counter value is less than the threshold value Th2, there is room for eliminating the closed and fixed state of the injection valve 31, and the abnormality determination unit 103 causes the return control unit 107 to execute the return control in step S62. The return control can be executed according to the same procedure as the return control in step S26 described above.

  After the return control by the return control unit 107 ends, the abnormality determination unit 103 counts up the second counter value in step S66, returns to step S18, and repeats the above-described flowchart from the clogging determination again.

  As described above, according to the control device 100 of the reducing agent injection device 20 according to the present embodiment, by controlling the reducing agent injection device 20, the abnormality of the injection valve 31 is detected by a relatively simple clogging determination. On the other hand, even if no abnormality is found due to the clogging determination, the abnormality of the injection valve 31 can be detected by the abnormality determination performed during the injection control. Further, in the abnormality determination performed during the injection control, it is possible to determine the presence or absence of the abnormality of the injection valve 31 while distinguishing between the open fixed state and the closed fixed state of the injection valve 31 without stopping the injection control. . Therefore, when there is no abnormality in the injection valve 31, the injection control of the urea aqueous solution can be continued.

  Further, the control device 100 of the reducing agent injection device 20 according to the present embodiment can distinguish between the open fixed state and the closed fixed state of the injection valve 31. Therefore, the injection control of the urea aqueous solution can be stopped promptly in the state where the injection valve 31 is open and fixed, and the dripping of the urea aqueous solution into the exhaust pipe 11 can be prevented. On the other hand, in the closed and fixed state of the injection valve 31, before the injection control of the urea aqueous solution is stopped, it is possible to try to eliminate the closed and fixed state of the injection valve 31 by the return control. As a result, only when it is determined that the abnormality of the injection valve 31 cannot be eliminated, the injection control of the urea aqueous solution is prohibited, and the injection control is not prohibited more than necessary.

  As described above, the preferred embodiments of the present invention have been described in detail with reference to the accompanying drawings, but the present invention is not limited to such examples. It is apparent that those skilled in the art to which the present invention pertains can conceive various changes or modifications within the scope of the technical idea described in the claims. It is understood that these also belong to the technical scope of the present invention.

Reference Signs List 5 internal combustion engine 10 urea SCR system 11 exhaust pipe 13 reduction catalyst 15 temperature sensor 20 reducing agent injection device 31 injection valve 41 pump 43 pressure sensor 50 storage tank 100 control device 101 injection control unit 103 abnormality determination unit 105 pressure determination unit 107 return control Department

Claims (8)

A reducing agent injection device that injects a reducing agent for purifying NOx in the exhaust gas of the internal combustion engine upstream of a reduction catalyst disposed in an exhaust passage by an injection valve attached to an exhaust pipe of the internal combustion engine. In a control device for controlling,
An injection control unit that controls the valve opening operation of the injection valve while controlling the output of a pump that pumps the reduction agent so that the pressure of the reducing agent supplied to the injection valve becomes a predetermined target value;
During execution of the injection control of the reducing agent, based on the current waveform supplied to the injection valve and the output of the pump, while determining whether the injection valve is open or closed and whether or not the injection valve is closed, An abnormality determination unit for determining abnormality;
A control device for a reducing agent injection device, comprising: The abnormality determination unit determines that the injection valve is in the open and fixed state when a change point does not appear in the current waveform and the output of the pump is maintained within a first range.
When no change point appears in the current waveform and the output of the pump is maintained within a second range smaller than the first range, the injection valve is in a closed and fixed state. The control device of the reducing agent injection device according to claim 1, wherein the determination is performed.   The control device for a reducing agent injection device according to claim 2, wherein the abnormality determination unit stops the injection control of the reducing agent when determining that the injection valve is in an open and fixed state.   When the abnormality determination unit determines that the injection valve is in the closed and fixed state, after once recovering the reducing agent supplied to the injection valve, a return control unit that resupplies the injection valve, A control device for a reducing agent injection device according to claim 2.   The reducing agent according to claim 4, wherein the abnormality determination unit prohibits execution of injection control of the injection valve when the number of times that the injection valve is determined to be in the closed and fixed state is equal to or greater than a predetermined threshold. Control device for injection device. When the reducing agent injection device is started and when the reducing agent is resupplied by the return control unit, the output of the pump that pumps the reducing agent while the pressure of the reducing agent supplied to the injection valve is increased is kept constant. A pressure determination unit that determines whether the injection valve is clogged based on the pressure of the reducing agent when the injection valve is maintained in the open state.
The injection control unit starts the control of the injection of the reducing agent when the pressure determination unit determines that there is no abnormality, and the abnormality determination unit determines abnormality of the injection valve. Of the reducing agent injection device.   The reducing agent according to claim 6, further comprising a return control unit that once collects the reducing agent supplied to the injection valve and resupplies the reducing agent to the injection valve when the pressure determination unit determines that there is an abnormality. Control device for injection device.   The control device of the reducing agent injection device according to claim 7, wherein the pressure determination unit prohibits execution of the injection control of the injection valve when the number of times of determining that there is an abnormality is equal to or greater than a predetermined threshold.

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