Control device and method for injecting urea water

Abstract

An exhaust pipe discharges exhaust gas discharged from a hydrogen engine to the outside of a vehicle. An exhaust purification device reduces nitrogen oxides contained in the exhaust gas. A nitrogen oxide sensor acquires a measurement value that reflects the concentration of the nitrogen oxides contained in the exhaust gas, and outputs an output value that is a value that is larger the more the amount of moisture contained in the exhaust gas is subtracted from the measurement value. An injector injects urea water to the exhaust purification device. A control device causes the injector to inject an amount of urea water determined in accordance with the output value and the flow rate of the exhaust gas, in a case where the output value is a predetermined value or more. The control device causes the injector to inject an amount of urea water determined in accordance with the predetermined value and the flow rate of the exhaust gas, in a case where the output value is less than the predetermined value.

Description

Technical Field

[0001] This invention relates to a control device and a method for spraying urea solution. Background Technology

[0002] Japanese Patent Application Publication No. 2010-71192 describes an exhaust system. The exhaust system includes an exhaust purification device, an injector, and a nitrogen oxide (NOx) sensor.

[0003] The exhaust purification system contains a catalyst for ammonia adsorption. It uses ammonia to reduce NOx in the exhaust gas emitted by the engine. Urea is added to the system as a reducing agent by injectors. A nitrogen oxide sensor measures the concentration of NOx in the exhaust gas flowing upstream of the purification system.

[0004] The exhaust system determines the amount of urea solution to be injected into the exhaust purification unit by the injector based on the measurement value of the nitrogen oxide sensor. Then, the exhaust system causes the injector to inject the determined amount of urea solution.

[0005] In addition to NOx in exhaust gas, nitrogen oxide sensors also react to moisture in the exhaust gas. Therefore, the readings from nitrogen oxide sensors can sometimes be higher than the values ​​that reflect the concentration of NOx contained in the exhaust gas.

[0006] The exhaust system corrects the nitrogen oxide sensor's measurement based on the water content in the exhaust gas, and then determines the amount of urea water to be injected by the injector. Summary of the Invention

[0007] As a way to correct exhaust system measurements, an arbitrary value can be subtracted from the actual measurement based on the NOx sensor. If the measurement falls below zero, it can be considered zero. In this case, the higher the water content in the exhaust, the larger the value subtracted from the measurement.

[0008] When an engine uses hydrogen as fuel, the water content in the exhaust increases. Therefore, when an engine uses hydrogen as fuel, the value subtracted from the measured value by the exhaust system also increases.

[0009] The responsiveness of a nitrogen oxide (NOx) sensor to moisture in exhaust gas varies not only depending on the moisture content but also on the exhaust flow rate and the sensor's temperature. Exhaust flow rate or sensor temperature are conditions where the sensor is less reactive to moisture; conversely, this can occur in environments with high moisture content and a larger subtraction from the measured value. In such cases, even if NOx is present in the exhaust, the corrected measurement may sometimes be zero. In these situations, the exhaust system does not inject urea solution, thus allowing NOx to pass through the exhaust purification device.

[0010] To address the aforementioned issues, the control device uses the output value of the nitrogen oxide sensor in the exhaust system to control the injectors.

[0011] The exhaust system includes an exhaust pipe that discharges exhaust gas from a hydrogen engine that uses hydrogen as fuel to the outside of the vehicle.

[0012] The exhaust system includes an exhaust purification device, which is located in the middle of the exhaust pipe and reduces the nitrogen oxides contained in the exhaust.

[0013] The exhaust system includes the nitrogen oxide sensor, which is located upstream of the exhaust purification device in the exhaust pipe. The nitrogen oxide sensor acquires a measurement value reflecting the concentration of nitrogen oxides contained in the exhaust and outputs an output value, which is the difference between the measured value and the value of the amount of water contained in the exhaust.

[0014] The exhaust system includes the injector, which is located in the exhaust pipe at a position further downstream of the nitrogen oxide sensor and further upstream of the exhaust purification device, and sprays urea water onto the exhaust purification device.

[0015] When the output value is above a predetermined value, the control device causes the injector to spray a certain amount of urea water based on the output value and the exhaust flow rate.

[0016] When the output value is less than the predetermined value, the control device causes the injector to spray a certain amount of urea water determined based on the predetermined value and the flow rate.

[0017] The urea water injection method proposed to solve the above problems is a urea water injection method in the exhaust system.

[0018] The exhaust system includes an exhaust pipe that discharges exhaust gas from a hydrogen engine that uses hydrogen as fuel to the outside of the vehicle.

[0019] The exhaust system includes an exhaust purification device, which is located in the middle of the exhaust pipe and reduces the nitrogen oxides contained in the exhaust.

[0020] The exhaust system includes a nitrogen oxide sensor, which is located upstream of the exhaust purification device in the exhaust pipe. The nitrogen oxide sensor acquires a measurement reflecting the concentration of nitrogen oxides contained in the exhaust and outputs an output value. The output value is the difference between the measured value and the value that is larger the amount of water contained in the exhaust.

[0021] The exhaust system includes an injector located in the exhaust pipe further downstream of the nitrogen oxide sensor and further upstream of the exhaust purification device, and injects urea water into the exhaust purification device.

[0022] The exhaust system includes a control device that controls the injector by acquiring the output value of the nitrogen oxide sensor.

[0023] The urea water injection method includes the following steps: when the output value is above a predetermined value, the control device determines the amount of urea water injected by the injector based on the output value and the exhaust flow rate; when the output value is below the predetermined value, the control device determines the amount of urea water injected by the injector based on the predetermined value and the flow rate.

[0024] The urea water injection method includes the following steps: after the control device determines the amount of urea water, it is injected into the exhaust purification device by the injector.

[0025] The aforementioned control device and urea water injection method can reduce the amount of nitrogen oxides passing through the exhaust purification device. Attached Figure Description

[0026] Hereinafter, with reference to the accompanying drawings, the features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described, in which the same reference numerals denote the same elements, and wherein:

[0027] Figure 1 This is a schematic diagram showing the configuration of an exhaust system equipped with a control device according to one embodiment.

[0028] Figure 2 This is a schematic diagram showing the arrangement of the units in a nitrogen oxide sensor.

[0029] Figure 3 This is a schematic diagram showing the internal structure of a nitrogen oxide sensor.

[0030] Figure 4 It means Figure 1 A flowchart of a series of processes performed by the control device.

[0031] Figure 5 It means Figure 1 The control device determines the injection volume of urea water based on the injector.

[0032] Figure 6 It means Figure 1The control device corrects the output value of the nitrogen oxide sensor in the following graphs: Graph (a) shows the shift of the output value of the nitrogen oxide sensor from the set value, Graph (b) shows the shift of the amount of urea added, and Graph (c) shows the shift of the nitrogen oxide concentration after purification. Detailed Implementation

[0033] The following is for reference. Figures 1 to 6 One embodiment of the control device will be described.

[0034] Composition of exhaust system 100

[0035] like Figure 1 As shown, the exhaust system 100 is suitable for vehicles equipped with a hydrogen engine 11. The hydrogen engine 11 uses hydrogen as fuel.

[0036] like Figure 1 As shown, the exhaust system 100 includes an exhaust pipe 14. The exhaust from the hydrogen engine 11 is discharged to the outside of the vehicle through the exhaust pipe 14.

[0037] like Figure 1 As shown, the exhaust system 100 includes an exhaust purification device 12. The exhaust purification device 12 is located midway through the exhaust pipe 14. The exhaust purification device 12 is a selective catalytic reduction (SCR) catalyst that uses ammonia (NH3) as a reducing agent to reduce nitrogen oxides (NOx) in the exhaust gas. NH3 generated from the hydrolysis of urea is adsorbed in the exhaust purification device 12.

[0038] like Figure 1 As shown, the exhaust system 100 includes a nitrogen oxide sensor 15. The nitrogen oxide sensor 15 is located upstream of the exhaust purification device 12 in the exhaust pipe 14. The nitrogen oxide sensor 15 measures the concentration of NOx contained in the exhaust gas.

[0039] like Figure 1 As shown, the exhaust system 100 includes an injector 13. The injector 13 is located in the exhaust pipe 14, downstream of the nitrogen oxide sensor 15 and upstream of the exhaust purification device 12. The injector 13 adds urea to the exhaust purification device 12 by spraying urea water toward the exhaust purification device 12.

[0040] like Figure 1 As shown, the exhaust system 100 includes a urea water tank 16. The urea water tank 16 is connected to the injector 13. The urea water tank 16 stores the urea water injected by the injector 13.

[0041] like Figure 1 As shown, the exhaust system 100 includes a control device 10. The control device 10 controls the injection of urea water based on the injector 13.

[0042] Composition and function of nitrogen oxide sensor 15

[0043] The following is for reference. Figure 2 and Figure 3 The structure and function of the nitrogen oxide sensor 15 are explained.

[0044] The nitrogen oxide sensor 15 has multiple units for measuring the concentration of NOx contained in exhaust gas. Figure 2 This indicates the configuration of the units in the nitrogen oxide sensor 15.

[0045] like Figure 2 As shown, the nitrogen oxide sensor 15 includes a pump unit 17, a sensor unit 18, and a monitoring unit 19. Figure 2 The solid arrow in the image indicates the direction in which exhaust gas flows into the nitrogen oxide sensor 15.

[0046] Figure 3 Indicates from Figure 2 The position of A in the middle is facing Figure 2 The direction of the dashed arrow in the image shows the internal structure of the nitrogen oxide sensor 15 when observing the nitrogen oxide sensor 15.

[0047] like Figure 3 As shown, the nitrogen oxide sensor 15 is separated by a first gas chamber 23 and a second gas chamber 24. Figure 3 In the image, the solid arrow indicates the direction in which exhaust gas flows into the nitrogen oxide sensor 15. For example... Figure 3 As shown, the exhaust gas flowing into the nitrogen oxide sensor 15 passes through the first gas chamber 23.

[0048] like Figure 3 As shown, the nitrogen oxide sensor 15 includes a heater 22. As described later, each unit in the nitrogen oxide sensor 15 causes components in the exhaust gas to react on the electrodes. The heater 22 is provided to facilitate the reaction on the electrodes by increasing the temperature of the nitrogen oxide sensor 15 when the temperature of the nitrogen oxide sensor 15 is low.

[0049] like Figure 2 and Figure 3 As shown, the exhaust gas flowing into the nitrogen oxide sensor 15 first flows into the pump unit 17 of the multiple units. (As indicated...) Figure 3 As shown, in the pump unit 17, two electrodes, a pump electrode 25 and a reference electrode 21, are provided in a manner that clamps the solid electrolyte body 20. The solid electrolyte body 20 is made of a substance that allows oxygen ions to pass through.

[0050] The pump electrode 25 is made of a material that is highly reactive with oxygen and lowly reactive with NOx. For example, the pump electrode 25 is made of platinum and gold as the main components.

[0051] If a voltage is applied to the pump electrode 25, the oxygen in the exhaust gas at the pump electrode 25 is reduced to oxygen ions. Figure 3 The dashed arrows in the diagram indicate the direction of oxygen ion movement. Oxygen ions generated within pump unit 17 are released from reference electrode 21 into the second gas chamber 24 via solid electrolyte 20.

[0052] Thus, pump unit 17 has the function of removing oxygen from exhaust gas. Furthermore, the current flowing through pump unit 17 reflects the oxygen concentration in the exhaust gas. Therefore, nitrogen oxide sensor 15 can determine the air-fuel ratio based on the current value flowing through pump unit 17.

[0053] like Figure 2 As shown, the sensor unit 18 and the monitoring unit 19 are arranged so that they flow into the exhaust gas passing through the pump unit 17. Figure 2 In the middle, viewed from position A, sensor unit 18 is located further forward than monitoring unit 19.

[0054] Like the pump unit 17, the sensor unit 18 and monitoring unit 19 are equipped with two electrodes in a manner that clamps the solid electrolyte body 20. Figure 3 In the middle, it shows from Figure 2 The sensor unit 18 is visible at position A in the diagram, and the monitoring unit 19 is located deep within the sensor unit 18.

[0055] In the monitoring unit 19, two electrodes, a monitoring electrode 27 and a reference electrode 21, are disposed in a manner that clamps the solid electrolyte body 20. Like the pump electrode 25, the monitoring electrode 27 is composed of a substance that is highly reactive with oxygen and lowly reactive with NOx. For example, the monitoring electrode 27 is composed primarily of platinum and gold.

[0056] Oxygen that is not completely removed in pump unit 17 flows into sensor unit 18 and monitoring unit 19. If a voltage is applied to monitoring electrode 27, the oxygen in the exhaust gas at monitoring electrode 27 is reduced to oxygen ions. The oxygen ions generated in monitoring unit 19 are released from reference electrode 21 into second gas chamber 24 through solid electrolyte 20.

[0057] The current flowing through the monitoring unit 19 reflects the oxygen concentration in the exhaust gas passing through the monitoring unit 19. Therefore, the nitrogen oxide sensor 15 can determine the oxygen concentration in the exhaust gas passing through the pump unit 17 based on the current value flowing through the monitoring unit 19.

[0058] In the sensor unit 18, two electrodes, a sensor electrode 26 and a reference electrode 21, are disposed in a manner that clamps the solid electrolyte body 20. The sensor electrode 26 is made of a substance that is highly reactive with NOx. For example, the monitoring electrode 27 is made of platinum and rhodium as the main components.

[0059] If a voltage is applied to sensor electrode 26, NOx in the exhaust gas at sensor electrode 26 is reduced to generate oxygen ions. The oxygen ions generated in sensor unit 18 are released from reference electrode 21 into second gas chamber 24 through solid electrolyte 20.

[0060] The current flowing through sensor unit 18 reflects the concentration of NOx in the exhaust gas. Therefore, nitrogen oxide sensor 15 can determine the concentration of NOx in the exhaust gas based on the current value flowing through sensor unit 18.

[0061] In the sensor electrode 26, in addition to NOx, oxygen from the pump unit 17 also reacts with the sensor electrode 26 to generate oxygen ions. Therefore, the NOx sensor 15 can measure the concentration of NOx in the exhaust gas by calculating the difference between the current value of the sensor unit 18 and the current value of the monitoring unit 19. In this way, the NOx sensor 15 can obtain a measurement value reflecting the concentration of NOx contained in the exhaust gas.

[0062] Output method based on the output value of nitrogen oxide sensor 15

[0063] In addition to NOx or oxygen, sensor electrode 26 also reacts with moisture in the exhaust gas. The moisture reacting with sensor electrode 26 produces oxygen ions. Therefore, the measured value in nitrogen oxide sensor 15 becomes higher than the actual concentration of NOx contained in the exhaust gas.

[0064] The nitrogen oxide sensor 15 outputs an output value based on the acquired measurement. The output value is a correction of the measurement value to account for moisture in the exhaust gas.

[0065] The amount of moisture contained in the exhaust can be estimated based on the air-fuel ratio. The nitrogen oxide sensor 15, for example, stores a mapping representing the relationship between the pre-measured air-fuel ratio and the amount of moisture contained in the exhaust of the hydrogen engine 11.

[0066] The nitrogen oxide sensor 15 measures the air-fuel ratio based on the current value of the pump unit 17. Then, the nitrogen oxide sensor 15 estimates the water content in the exhaust gas based on the obtained air-fuel ratio.

[0067] After estimating the moisture content in the exhaust gas, the nitrogen oxide sensor 15 corrects the measured value based on the estimated moisture content, thereby outputting an output value. Specifically, the nitrogen oxide sensor 15 uses the value obtained by subtracting an arbitrary value from the measured value as the output value, and treats the output value as zero if it is below zero. In this case, the nitrogen oxide sensor 15 increases the value subtracted from the measured value based on the estimated moisture content.

[0068] Functions of control device 10

[0069] like Figure 1 As shown, the control device 10 is communicatively connected to the injector 13 and the nitrogen oxide sensor 15. The control device 10 acquires the output value from the nitrogen oxide sensor 15. After determining the injection amount of urea solution based on the acquired output value, the control device 10 causes the injector 13 to inject the determined amount of urea solution.

[0070] As described above, the output value is obtained by subtracting the value that increases with the amount of water in the exhaust from the measured value. The hydrogen engine 11 uses hydrogen as fuel, thus its exhaust contains a large amount of water. Therefore, when outputting the output value, the value subtracted from the measured value by the nitrogen oxide sensor 15 tends to be larger.

[0071] On the other hand, in sensor unit 18, the degree to which moisture reacts with sensor electrode 26 is also affected by the temperature of nitrogen oxide sensor 15 or the exhaust flow rate. The lower the temperature of nitrogen oxide sensor 15, the lower the degree of reaction between moisture and sensor electrode 26. The slower the exhaust flow rate, the lower the degree of reaction between moisture and sensor electrode 26. Therefore, depending on the temperature of nitrogen oxide sensor 15 or the exhaust flow rate, the value subtracted when outputting the output value becomes too large. Furthermore, in vehicles using hydrogen engine 11, the value subtracted from the measured value by nitrogen oxide sensor 15 tends to be large, thus the value subtracted when outputting the output value tends to be too large.

[0072] Furthermore, as described above, when the temperature of the nitrogen oxide sensor 15 is low, the heater 22 operates in a manner that ensures sufficient reaction between the electrode and components in the exhaust gas. Since the exhaust gas from the hydrogen engine 11 contains a large amount of moisture, its temperature tends to drop. Therefore, the heater 22 operates more frequently, and thus is prone to deterioration over time. If the heater 22 deteriorates over time, the reactivity of the electrode with components in the exhaust gas decreases, thereby reducing the reactivity of NOx in the sensor unit 18 with the sensor electrode 26.

[0073] Thus, in vehicles using the hydrogen engine 11, the output value of the nitrogen oxide sensor 15 tends to decrease. Therefore, it is possible to consider the case where, even when NOx is present in the exhaust, the output value after correction by subtracting the measured value is below zero. Taking this situation into account, the control device 10 corrects the output value according to the conditions in the vehicle and determines the injection quantity of urea water based on the injector 13.

[0074] Processing method based on control device 10

[0075] Figure 4 This indicates a series of processes performed by control device 10. Control device 10 performs these processes at constant intervals during the operation of the hydrogen engine 11. Figure 4 The series of processes shown.

[0076] In process S11, the control device 10 confirms the vehicle's status. At this time, the control device 10 confirms whether the vehicle is in a fuel cutoff period, as part of its status. Furthermore, the control device 10 confirms whether the nitrogen oxide sensor 15 is active, as part of its status. The control device 10 confirms the operating status of the hydrogen engine 11, including the intake air volume of the hydrogen engine 11, as part of its status. Having confirmed the vehicle's status, the control device 10 proceeds to process S12.

[0077] In process S12, the control device 10 determines the injection volume of urea solution based on the injector 13. To ensure the exhaust gas purification device 12 fully reduces NOx in the exhaust gas, it is preferable to inject more urea solution when the exhaust gas contains more NOx, thus adding more urea to the exhaust gas purification device 12. The control device 10 determines the injection volume of urea solution based on the injector 13 according to the concentration of NOx in the exhaust gas and the exhaust gas flow rate.

[0078] The control device 10 estimates the exhaust flow rate, for example, based on the intake air volume in the vehicle. The control device 10 changes the type of value used for the NOx concentration in the exhaust according to the vehicle's condition.

[0079] Figure 5 This indicates the method by which the control device 10 determines the injection volume of urea water based on the injector 13 during the processing in S12.

[0080] When the nitrogen oxide sensor 15 is not in an active state, the measured value and output value do not accurately reflect the concentration of NOx in the exhaust gas. For example... Figure 5 As shown, when the nitrogen oxide sensor 15 is in an inactive state, the control device 10 determines the injection volume of urea water based on the estimated NOx concentration and the exhaust flow rate.

[0081] The concentration of NOx in the exhaust can be estimated based on the operating conditions of the hydrogen engine 11. The operating conditions of the hydrogen engine 11 include, for example, the magnitude of the torque output by the hydrogen engine 11 or the rotational speed of the hydrogen engine 11. The control device 10 outputs an estimated NOx concentration, for example, by referring to a pre-made mapping showing the relationship between the operating conditions of the hydrogen engine 11 and the concentration of NOx in the exhaust. The operating conditions of the hydrogen engine 11 include, in addition to the intake air volume, factors such as, the rotational speed of the output shaft of the hydrogen engine 11, the valve timing of the intake and exhaust valves, the ignition timing, the opening degree of the EGR valve, and the exhaust temperature.

[0082] like Figure 5As shown, the control device 10 sometimes has the nitrogen oxide sensor 15 active and not during fuel cut-off. In this case, the urea water injection quantity is determined based on the output value of the nitrogen oxide sensor 15, which is corrected to an output value with a predetermined lower limit, and the exhaust flow rate.

[0083] As described above, in vehicles using the hydrogen engine 11, it is possible to consider cases where the output value is below zero even when NOx is present in the exhaust. When the nitrogen oxide sensor 15 is active and not during fuel cutoff, the control device 10 corrects the output value so that a predetermined value greater than zero is used as the lower limit of the output value.

[0084] Figure 6 This indicates the shift in the output value of the nitrogen oxide sensor 15, the amount of urea added to the exhaust purification device 12, and the concentration of NOx contained in the exhaust gas purified by the exhaust purification device 12. Additionally, in Figure 6 In the original text, the output value is less than zero ppm, but in the control device 10, the output value less than zero ppm is processed as zero ppm.

[0085] Figure 6 In the output value shifts shown in Graph (a), the shifts in output values ​​not corrected by the control device 10 are represented by dashed lines, while the shifts in output values ​​used by the control device 10 when determining the injection volume of urea water are represented by solid lines.

[0086] exist Figure 6 In the diagram, R1 and R2 represent the periods during which the nitrogen oxide sensor 15 is active and not during the fuel cut-off period.

[0087] exist Figure 6 In Chart (a), the given value is 3 ppm. The given value is determined based on the concentration of NOx contained in the exhaust gas when the vehicle is idling.

[0088] exist Figure 6 During the R1 period of graph (a), the output value is less than the predetermined value. Figure 6 As shown in Figure (a), the control device 10 corrects the output value to the predetermined value when the output value is less than the predetermined value. That is, when the nitrogen oxide sensor 15 is active and not during the fuel cut-off period, the control device 10 determines the amount of urea water injection based on the predetermined value and the exhaust flow rate when the output value is less than the predetermined value.

[0089] exist Figure 6 For the period of R² in graph (a), the output value is above a predetermined value. Figure 6As shown, the control device 10 does not correct the output value if the output value is above a predetermined value. That is, when the nitrogen oxide sensor 15 is in an active state and not during the fuel cut-off period, the control device 10 determines the urea water injection quantity based on the output value and the exhaust flow rate if the output value is above a predetermined value.

[0090] like Figure 5 As shown, when the nitrogen oxide sensor 15 is in an active state and during fuel cut-off, the control device 10 determines the injection amount of urea water based on the output value of the nitrogen oxide sensor 15 and the flow rate of the exhaust gas. Figure 6 The duration of the fuel cutoff is shown in the diagram. (Example) Figure 6 As shown in Figure (a), during the fuel cut-off period, the control device 10 does not perform a correction on the output value by using a predetermined value as the lower limit. As described above, at this time, the control device 10 processes output values ​​less than zero ppm to zero ppm.

[0091] The control device 10, having determined the injection volume of urea solution as described above, initiates process S13. In process S13, the control device 10 causes the injector 13 to inject the amount of urea solution determined in process S12. Then, the control device 10 terminates the process. Figure 4 The series of processes shown.

[0092] Thus, even when the output value is less than zero, as long as the constant condition is met, the control device 10 determines the amount of urea water to be injected based on the output value that has been corrected by using a predetermined value as the lower limit.

[0093] exist Figure 6 In graph (b), the shift in the amount of urea added, where the injection rate of urea solution is determined based on the output value before correction by control device 10, is represented by a dashed line. Figure 6 In graph (b), the shift in the amount of urea added, where the injection rate of urea solution is determined based on the output value corrected by control device 10, is represented by a solid line. Figure 6 As shown in Figure (b), the control device 10 can enable the injector 13 to add urea even during periods when urea cannot be added by correcting the output value.

[0094] exist Figure 6 In graph (c), the shift in NOx concentration in the exhaust gas after the exhaust purification device 12 is represented by a dashed line, assuming the urea water injection rate is determined based on the output value before correction by the control device 10. Figure 6In graph (c), the shift in NOx concentration in the exhaust gas after the exhaust purification device 12 is represented by a solid line, where the injection rate of urea solution is determined based on the output value corrected by the control device 10. Figure 6 As shown in Figure (c), urea is not added even if NOx is present in the exhaust when the output value is not corrected, but urea is added when the output value is corrected, thus reducing NOx emissions to the outside of the vehicle.

[0095] The function of this implementation method

[0096] The control device 10 sets a constant lower limit on the output value of the nitrogen oxide sensor 15, so that the injector 13 sprays urea water even when the output value of the nitrogen oxide sensor 15 should be zero.

[0097] Effects of this implementation method

[0098] (1) The control device 10 can reduce the amount of NOx passing through the exhaust purification device 12.

[0099] (2) During the fuel cut-off period, the control device 10 causes the injector 13 to spray a urea solution amount determined based on the output value and flow rate. During the fuel cut-off period, the hydrogen engine 11 does not emit NOx. Therefore, during the fuel cut-off period, when the output value of the NOx sensor 15 becomes zero, it is preferable that the injector 13 does not spray urea solution. During the fuel cut-off period, the control device 10 determines the amount of urea solution sprayed by the injector 13 based on the output value without a set lower limit value rather than the output value with a set lower limit value. Thus, the control device 10 can prevent the injector 13 from spraying urea solution when the hydrogen engine 11 does not generate NOx.

[0100] (3) The predetermined value is determined based on the concentration of NOx contained in the exhaust gas when the vehicle is idling. When the predetermined value is large, the possibility of the injector 13 injecting too much urea water is higher relative to the concentration of NOx contained in the exhaust gas. The control device 10 uses the predetermined value determined based on the concentration of NOx emitted by the hydrogen engine 11 when the vehicle is idling. Thus, the control device 10 is able to prevent the injector 13 from excessively injecting urea water.

[0101] (4) When the nitrogen oxide sensor 15 is inactive, the concentration of NOx contained in the exhaust gas is estimated based on the operating status of the hydrogen engine 11. The control device 10 causes the injector 13 to inject a urea solution of a quantity determined based on the estimated NOx concentration and flow rate.

[0102] When the nitrogen oxide sensor 15 is not in an active state, the measured value and output value do not accurately reflect the NOx concentration in the exhaust gas. In the absence of the nitrogen oxide sensor 15, the control device 10 determines the amount of urea solution injected by the injector 13 based on the estimated NOx concentration, rather than using the measured value and output value. Therefore, the control device 10 can more precisely determine the amount of urea solution injected by the injector 13.

[0103] (5) The exhaust system 100 includes an exhaust pipe 14, an exhaust purification device 12, a nitrogen oxide sensor 15, an injector 13, and a control device 10. The exhaust pipe 14 discharges the exhaust gas from the hydrogen engine 11, which uses hydrogen as fuel, to the outside of the vehicle. The exhaust purification device 12 is located in the middle of the exhaust pipe 14 and reduces the NOx contained in the exhaust gas. The nitrogen oxide sensor 15 is located in the exhaust pipe 14 at a position upstream of the exhaust purification device 12. The nitrogen oxide sensor 15 acquires a measurement value reflecting the concentration of NOx contained in the exhaust gas and outputs a value obtained by subtracting a value that increases with the amount of water contained in the exhaust gas from the measured value. The injector 13 is located in the exhaust pipe 14 at a position downstream of the nitrogen oxide sensor 15 and upstream of the exhaust purification device 12, and injects urea water into the exhaust purification device 12. The control device 10 acquires the output value of the nitrogen oxide sensor 15 to control the injector 13. In the urea water injection method, when the output value is above a predetermined value, the control device 10 determines the amount of urea water injected by the injector 13 based on the output value and the exhaust flow rate. Furthermore, when the output value is below the predetermined value, the control device 10 determines the amount of urea water injected by the injector 13 based on the predetermined value and the exhaust flow rate (S12). The urea water injection method includes the step of the injector 13 injecting the amount of urea water determined by the control device 10 into the exhaust purification device 12 (S13).

[0104] In the urea water injection method, by setting a constant lower limit value on the output value of the nitrogen oxide sensor 15, the injector 13 injects urea water even when the output value of the nitrogen oxide sensor 15 should be zero. Therefore, the urea water injection method can reduce the amount of NOx passing through the exhaust gas purification device 12.

[0105] Change Example

[0106] The above-described embodiments can be implemented in the following ways. The above-described embodiments and the following modifications can be combined with each other to implement them without causing technical inconsistencies.

[0107] In the above embodiment, the control device 10 is sometimes in an active state when the nitrogen oxide sensor 15 is in a fuel cut-off period. In this case, the amount of urea water to be injected by the injector 13 is determined based on the output value, which is not corrected to a predetermined value as a lower limit, and the exhaust flow rate.

[0108] When the nitrogen oxide sensor 15 is active and during fuel cut-off, the control device 10 can also inject urea water into the injector 13 based on the output value and flow rate, which are determined by implementing a correction with a predetermined value as the lower limit.

[0109] Furthermore, the control device 10 can also be configured to prevent the injector 13 from spraying urea water when the nitrogen oxide sensor 15 is active and during fuel cut-off, regardless of the output value and flow rate.

[0110] The predetermined value can also be determined based on the concentration of NOx contained in the exhaust gas when the vehicle is idling. For example, the predetermined value can be arbitrarily determined by the designer of the control device 10.

[0111] In the above embodiment, the control device 10 determines the amount of urea solution based on the estimated NOx concentration and the exhaust flow rate when the nitrogen oxide sensor 15 is inactive. Alternatively, the control device 10 can also determine the amount of urea solution based on the output value and the exhaust flow rate when the nitrogen oxide sensor 15 is inactive.

Claims

1. A control device for an exhaust system, comprising controlling an injector by acquiring the output value of a nitrogen oxide sensor, the exhaust system comprising: The exhaust pipe discharges the exhaust gas from the hydrogen-fueled engine to the outside of the vehicle. An exhaust purification device is installed in the middle of the exhaust pipe and reduces the nitrogen oxides contained in the exhaust. A nitrogen oxide sensor, disposed in the exhaust pipe upstream of the exhaust purification device, acquires a measurement reflecting the concentration of nitrogen oxides in the exhaust gas and outputs an output value, wherein the output value is the difference between the measured value and the value of moisture contained in the exhaust gas; and An injector, located in the exhaust pipe further downstream of the nitrogen oxide sensor and further upstream of the exhaust purification device, sprays urea solution into the exhaust purification device. The control device is characterized in that... When the output value is above a predetermined value, the injector sprays a quantity of urea solution determined based on the output value and the exhaust flow rate. If the output value is less than the predetermined value, the injector sprays a urea solution of a quantity determined based on the predetermined value and the flow rate.

2. The control device according to claim 1, characterized in that, During fuel cut-off, the injector sprays a urea solution of a quantity determined based on the output value and the flow rate.

3. The control device according to claim 1, characterized in that, The predetermined value is determined based on the concentration of nitrogen oxides contained in the exhaust gas when the vehicle is idling.

4. The control device according to claim 1, characterized in that, When the nitrogen oxide sensor is inactive, the concentration of nitrogen oxides in the exhaust gas is estimated based on the operating status of the hydrogen engine. The injector then sprays a volume of urea solution determined based on the estimated concentration of nitrogen oxides and the flow rate.

5. A method for injecting urea solution, which is a method for injecting urea solution in an exhaust system, said exhaust system comprising: The exhaust pipe discharges the exhaust gas from the hydrogen engine, which uses hydrogen as fuel, to the outside of the vehicle. An exhaust purification device is installed in the middle of the exhaust pipe and reduces the nitrogen oxides contained in the exhaust. A nitrogen oxide sensor is installed in the exhaust pipe at a position upstream of the exhaust purification device to acquire a measurement value reflecting the concentration of nitrogen oxides contained in the exhaust and output an output value, which is the difference between the measured value and the value that is larger the amount of water contained in the exhaust. An injector, disposed in the exhaust pipe at a position downstream of the nitrogen oxide sensor and upstream of the exhaust purification device, sprays urea solution into the exhaust purification device; and A control device that controls the injector by acquiring the output value of the nitrogen oxide sensor. The method for spraying urea solution is characterized by including the following steps: When the output value is above a predetermined value, the control device determines the amount of urea water injected by the injector based on the output value and the flow rate of the exhaust gas; when the output value is below the predetermined value, the control device determines the amount of urea water injected by the injector based on the predetermined value and the flow rate. After the control device determines the amount of urea solution, it is sprayed onto the exhaust purification device by the injector.

Images