Purification system

Abstract

To enable both of improvement of an exhaust gas purification rate and suppression of emission of ammonia to the atmosphere.SOLUTION: A purification system S includes: an engine 1; a catalyst 21 that purifies exhaust gas by causing adsorbed ammonia and nitrogen oxide included in exhaust gas of the engine 1 to react with each other; a motor 41 that is driven to compensate a difference between a load of the engine 1 and a drive load when the drive load of a driven device 5 driven by the engine 1 has changed; a battery 42 that supplies electric power to the motor 41; and a setting section that sets a target value of an adsorption amount of ammonia to be adsorbed to the catalyst 21 to a larger value as residual capacity of the battery 42 becomes larger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a purification system for purifying engine exhaust gas. [Background technology]

[0002] There are known technologies for purifying engine exhaust gas. Patent Document 1 discloses a technology for purifying exhaust gas by providing a catalyst in an engine exhaust passage that adsorbs ammonia and promotes a reaction between the adsorbed ammonia and nitrogen oxides in the exhaust gas. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-113580 Summary of the Invention [Problem to be solved by the invention]

[0004] When a large amount of ammonia is adsorbed on the catalyst, the ammonia reacts more easily with nitrogen oxides in the exhaust, improving the exhaust purification rate. However, if the temperature of the exhaust gas rises while a large amount of ammonia is adsorbed on the catalyst, there is a risk that the ammonia will desorb from the catalyst and be emitted into the atmosphere without reacting with nitrogen oxides.

[0005] The present invention has been made in view of these points, and aims to achieve both an improvement in the purification rate of exhaust gas and a suppression of ammonia emissions into the atmosphere. [Means for solving the problem]

[0006] One aspect of the present invention provides a purification system having an engine, a catalyst that purifies exhaust gas by causing a reaction between adsorbed ammonia and nitrogen oxides contained in the exhaust gas of the engine, a motor that assists the engine, a battery that supplies power to the motor, and an injection control unit that controls the amount of urea injected so that the amount of ammonia adsorbed on the catalyst increases as the remaining capacity of the battery increases.

[0007] The present invention may further include a setting unit that sets the target value so that the target value of the amount of ammonia adsorbed onto the catalyst increases as the remaining capacity of the battery increases, and the injection control unit may inject the urea so that the amount of ammonia adsorbed reaches the target value.

[0008] When the remaining capacity is less than a threshold value, the setting unit may set the target value of the amount of adsorption to a predetermined value.

[0009] The setting unit may set the target value to an upper limit target value of the amount of ammonia that can be adsorbed by the catalyst when the remaining capacity is equal to or greater than a predetermined value and the exhaust temperature of the engine is equal to an activation temperature of the catalyst.

[0010] The setting unit may set the upper limit target value to the target value when the target value determined according to the remaining capacity is greater than the limit of the adsorbable amount determined according to the exhaust temperature.

[0011] The engine may further include a drive control section that operates the engine in a steady state so that the exhaust temperature of the engine is equal to or higher than the activation temperature of the catalyst and the load on the engine is constant.

[0012] When the driving load of a driven device driven by the engine is greater than the load of the engine during steady operation, the drive control unit may cause the motor to output the difference between the load of the engine during steady operation and the driving load, and when the driving load is smaller than the load of the engine during steady operation, the drive control unit may cause the motor to function as a generator and generate electricity using the difference. [Effects of the Invention]

[0013] The present invention has the effect of achieving both an improvement in the purification rate of exhaust gas and a suppression of ammonia emissions into the atmosphere. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a diagram for explaining the configuration of a purification system according to an embodiment of the present invention. [Figure 2] FIG. 10 is a diagram for explaining the relationship between exhaust gas temperature and adsorption limit amount. [Figure 3] FIG. 2 is a diagram for explaining the configuration of a control device. [Figure 4] FIG. 10 is a diagram for explaining the relationship between remaining capacity and a target value. [Figure 5] 10 is a flowchart illustrating an example of a process for setting a target value. DETAILED DESCRIPTION OF THE INVENTION

[0015] [Configuration of Purification System S] FIG. 1 is a diagram for explaining the configuration of a purification system S according to this embodiment. The purification system S shown in FIG. 1 is a system that purifies the exhaust gas of an engine 1. The purification system S is installed in, for example, a vehicle, a ship, etc. In the following explanation, the purification system S will be described as being mounted on a vehicle. The purification system S has an engine 1, a purification device 2, a urea injection unit 3, a driven device 5, a control device 6, a motor 41, and a battery 42.

[0016] The engine 1 is an internal combustion engine that generates power by burning and expanding a mixture of fuel and intake air. The engine 1 is, for example, a diesel engine, but may also be a gasoline engine. A driven device 5 is connected to an output shaft 12 of the engine 1. The engine 1 drives the driven device 5.

[0017] The driven device 5 is, for example, a transmission, a drive shaft, and a wheel, but is not limited to these. In the following description, the load required to drive the driven device 5 may be referred to as a driving load.

[0018] The motor 41 is provided on the output shaft 12 between the engine 1 and the driven device 5. The motor 41 assists the engine 1 and drives the driven device 5. The motor 41 operates using power supplied from a battery 42. The motor 41 can also generate electricity by being driven by the power of the engine 1. In other words, the motor 41 also functions as a generator.

[0019] The purifier 2 is provided in an exhaust pipe 11 that discharges exhaust gas from the engine 1 to the outside, and purifies the exhaust gas from the engine 1. A catalyst 21 is provided inside the purifier 2. The catalyst 21 is a selective reduction catalyst that purifies the exhaust gas when it reaches or exceeds its activation temperature. The activation temperature is, for example, 200 degrees Celsius, but is not limited to this. The catalyst 21 purifies the exhaust gas by causing a reaction between nitrogen oxides and ammonia contained in the exhaust gas. Specifically, the catalyst 21 purifies the exhaust gas by promoting the reaction between nitrogen oxides and ammonia when it is above its activation temperature.

[0020] The urea injection unit 3 is provided in the exhaust pipe 11 between the engine 1 and the catalyst 21. The urea injection unit 3 injects urea, a precursor of ammonia, into the exhaust pipe 11. Specifically, the urea injection unit 3 injects urea water containing urea into the exhaust pipe 11. The urea in the urea water injected into the exhaust pipe 11 is hydrolyzed by the heat of the exhaust gas to become ammonia. The ammonia is adsorbed onto the catalyst 21. The catalyst 21 purifies the exhaust gas by promoting the reaction between the adsorbed ammonia and nitrogen oxides.

[0021] When a large amount of ammonia is adsorbed on the catalyst 21, the ammonia is more likely to react with nitrogen oxides in the exhaust, improving the purification rate of the exhaust gas. However, the amount of ammonia that can be adsorbed on the catalyst 21 is determined according to the temperature of the catalyst 21. Therefore, when the temperature of the catalyst 21 rises due to an increase in the exhaust gas temperature, the amount of ammonia that can be adsorbed on the catalyst 21 decreases, and the ammonia is desorbed from the catalyst 21.

[0022] FIG. 2 is a diagram illustrating the relationship between exhaust gas temperature and the adsorption limit amount. The horizontal axis of FIG. 2 represents exhaust gas temperature T, and the vertical axis represents the amount Q of ammonia adsorbed to the catalyst 21. The adsorption limit amount L is a graph showing the adsorption limit amount of ammonia that can be adsorbed according to the exhaust gas temperature T. The higher the exhaust gas temperature T, the smaller the adsorption limit amount L. The activation temperature E is the temperature at which the catalyst 21 becomes activated and can purify the exhaust gas. Note that the exhaust gas temperature T and the temperature of the catalyst 21 are linked, so when the exhaust gas temperature T reaches or exceeds the activation temperature E, the catalyst 21 also reaches or exceeds the activation temperature E. Below, the desorption of ammonia will be explained assuming that the temperature of the catalyst 21 and the exhaust gas temperature T are equal.

[0023] For example, if the exhaust gas temperature T is the activation temperature E and the adsorption amount Q of ammonia is the first adsorption amount A, when the exhaust gas temperature T rises to temperature T1, the adsorption limit amount L of ammonia decreases, and so ammonia can only be adsorbed onto the catalyst 21 up to the second adsorption amount B. As a result, ammonia is desorbed from the catalyst 21 by an amount equal to the difference between the first adsorption amount A and the second adsorption amount B and is emitted into the atmosphere. Conversely, even if a large amount of ammonia is adsorbed onto the catalyst 21, if the exhaust gas temperature T does not rise, the ammonia will not be desorbed and will not be emitted into the atmosphere.

[0024] Therefore, in order to suppress the emission of ammonia into the atmosphere, the control device 6 operates the engine 1 in a steady state so that the load is constant, and causes the motor 41 to output the difference between the drive load of the driven device 5 and the load of the engine 1. The amount by which the motor 41 can compensate for the difference is determined by the remaining capacity of the battery 42, and the greater the remaining capacity of the battery 42, the greater the amount. For example, when the remaining capacity of the battery 42 is large, the motor 41 can compensate for the load difference for a long period of time. This allows the engine 1 to continue steady operation even if the drive load continues to be higher than the load during steady operation of the engine 1.

[0025] When the engine 1 is operating steadily, an increase in exhaust temperature is suppressed, so even if a large amount of ammonia is adsorbed on the catalyst 21, there is less risk of the ammonia being desorbed from the catalyst 21 due to an increase in exhaust temperature. When there is little risk of ammonia being desorbed, the control device 6 increases the amount of ammonia adsorbed on the catalyst 21. As the amount of ammonia adsorbed on the catalyst 21 increases, the catalyst 21 becomes more likely to purify the exhaust, improving the exhaust purification rate. In this way, the control device 6 can both suppress the emission of ammonia into the atmosphere and improve the exhaust purification rate. The configuration of the control device 6 will be described in detail below.

[0026] [Configuration of control device 6] 3 is a diagram illustrating the configuration of the control device 6. The control device 6 has a storage unit 61 and a control unit 62. The storage unit 61 is a storage medium including a ROM (Read Only Memory), a RAM (Random Access Memory), a hard disk, etc. The storage unit 61 stores a program executed by the control unit 62.

[0027] The control unit 62 is a computational resource including a processor such as a CPU (Central Processing Unit). The control unit 62 executes a program stored in the storage unit 61 to realize functions as an acquisition unit 621, a setting unit 622, an injection control unit 623, and a drive control unit 624.

[0028] The acquisition unit 621 acquires information about the purification system S. The acquisition unit 621 acquires, for example, the remaining capacity of the battery 42. The acquisition unit 621 acquires capacity information indicating the remaining capacity from a battery monitoring system that monitors the remaining capacity of the battery 42. The acquisition unit 621 may calculate the power consumption of the motor 41 from the output of the motor 41, and acquire the remaining capacity of the battery 42 by subtracting the power consumption of the motor 41 from the maximum capacity of the battery 42 to the present time from the maximum capacity of the battery 42.

[0029] The acquisition unit 621 acquires load information indicating the drive load of the driven device 5. For example, the acquisition unit 621 acquires the load information indicating the drive load of the driven device 5 from a sensor provided in the driven device 5. The sensor is, for example, a torque sensor that detects torque, but is not limited to this.

[0030] The setting unit 622 sets a target value for the amount of ammonia adsorbed on the catalyst 21. For example, the setting unit 622 sets a target value M according to the remaining capacity SOC. Fig. 4 is a diagram for explaining the relationship between the remaining capacity SOC and the target value M. The horizontal axis of Fig. 4 represents the remaining capacity SOC, and the vertical axis represents the target value M for the amount of adsorption.

[0031] The lower limit target value C is the amount of adsorption at which the exhaust purification rate of the catalyst 21 becomes a predetermined lower limit of the purification rate. The lower limit of the purification rate is set, for example, so that the amount of nitrogen oxides emitted into the atmosphere becomes less than the emission standard value. If the amount of ammonia adsorption falls below the lower limit target value C, there will be insufficient ammonia relative to the nitrogen oxides, and the exhaust cannot be sufficiently purified.

[0032] The setting unit 622 sets a target value M of the adsorption amount that allows the catalyst 21 to purify the exhaust gas even when the remaining capacity SOC is small. Specifically, when the remaining capacity SOC is less than a threshold value D, the setting unit 622 sets the target value M to a lower limit target value C. This allows the setting unit 622 to make the purification rate of the exhaust gas equal to or greater than the purification rate lower limit value even when the remaining capacity SOC is small.

[0033] The upper limit target value A1 is the limit value for the amount of ammonia that can be adsorbed by the catalyst 21 when the exhaust temperature is the activation temperature E, and is equal to the first adsorption amount A (see FIG. 2). When ammonia in an amount greater than the upper limit target value A1 is supplied to the catalyst 21 at the activation temperature E, some of the supplied ammonia cannot be adsorbed by the catalyst 21 and is emitted into the atmosphere. When the exhaust temperature is below the activation temperature E, the catalyst 21 can adsorb a greater amount of ammonia than the upper limit target value A1, but cannot promote the reaction between the adsorbed ammonia and nitrogen oxides. Therefore, it is not necessary to supply ammonia in an amount greater than the upper limit target value A1.

[0034] The setting unit 622 sets a target value M equal to or less than the upper limit target value A1 in order to suppress unnecessary supply of ammonia. Specifically, when the remaining capacity SOC is equal to or greater than a predetermined value F that is greater than the threshold value D, the setting unit 622 sets the target value M to the upper limit target value A1. More specifically, when the exhaust temperature is the activation temperature E and the remaining capacity SOC is equal to or greater than the predetermined value F, the setting unit 622 sets the target value M to the upper limit target value A1. The predetermined value F is 80% of the maximum capacity of the battery 42, but is not limited to this and may be the maximum capacity. In this way, the setting unit 622 can suppress the supply of an unnecessarily large amount of ammonia.

[0035] When the remaining capacity SOC is equal to or greater than threshold D and less than predetermined value F, setting unit 622 sets target value M that is greater than lower limit target value C as the remaining capacity SOC increases. Setting unit 622 sets target value M corresponding to the remaining capacity SOC acquired by acquisition unit 621 by referring to relationship information indicating the relationship between target value M and remaining capacity SOC. The relationship information is a data table that associates target value M with each of a plurality of remaining capacities SOC. The data table is stored in, for example, storage unit 61. In this way, setting unit 622 can increase target value M for the adsorption amount as the amount by which motor 41 can compensate for the difference increases, thereby improving the purification rate of exhaust gas.

[0036] The injection control unit 623 injects urea water from the urea injection unit 3. The injection control unit 623 injects urea (urea water) from the urea injection unit 3 so that the amount of ammonia adsorbed by the catalyst 21 becomes the target value M set by the setting unit 622. Specifically, first, the injection control unit 623 estimates an estimated adsorption amount of ammonia currently adsorbed on the catalyst 21 based on the amount of exhaust gas discharged from the exhaust pipe 11 and the amount of urea water injected up to the present time. Next, the injection control unit 623 identifies the difference between the estimated adsorption amount and the target value M.

[0037] Then, the injection control unit 623 causes the urea injection unit 3 to inject an amount of urea water according to the difference between the estimated adsorption amount and the target value M into the exhaust pipe 11. Specifically, when the estimated adsorption amount is less than the target value M, the injection control unit 623 increases the injection amount of urea water that the urea injection unit 3 injects as the difference between the estimated adsorption amount and the target value M increases. In this way, the injection control unit 623 can increase the amount of ammonia adsorbed on the catalyst 21. When the estimated adsorption amount is equal to or greater than the target value M, the injection control unit 623 does not cause the urea injection unit 3 to inject urea water. In this way, the injection control unit 623 can prevent ammonia from being supplied to the catalyst 21 more than necessary.

[0038] 2, when ammonia is supplied to the catalyst 21 in an amount exceeding the adsorption limit amount L, part of the supplied ammonia is discharged without being adsorbed by the catalyst 21. Therefore, the setting unit 622 sets the target value M so that the ammonia does not exceed the adsorption limit amount L. When the target value M determined according to the remaining capacity SOC is larger than the adsorption limit amount L determined according to the exhaust temperature, the setting unit 622 sets the adsorption limit amount L to the target value M. In this way, the setting unit 622 can prevent an unnecessarily large amount of ammonia from being supplied.

[0039] The drive control unit 624 controls the engine 1. When the setting unit 622 sets a target value M that is greater than the lower limit target value C, the drive control unit 624 causes the engine 1 to perform steady operation so that the load is constant. Specifically, the drive control unit 624 causes the engine 1 to perform steady operation so that the load is constant and the exhaust temperature is equal to or higher than the activation temperature E of the catalyst 21. More specifically, the drive control unit 624 causes the engine 1 to perform steady operation so that the exhaust temperature is equal to or higher than the activation temperature E and equal to or lower than the upper limit temperature F.

[0040] Incidentally, the magnitude relationship between the load on the engine 1 during steady operation and the drive load on the driven device 5 can be reversed. For example, when the vehicle is traveling uphill or accelerating, the drive load on the driven device 5 is greater than the load on the engine 1 during steady operation. On the other hand, when the vehicle is traveling downhill or coasting, the drive load on the driven device 5 is smaller than the load on the engine 1 during steady operation.

[0041] Therefore, the drive control unit 624 causes the motor 41 to output power or generate power depending on the magnitude relationship between the load on the engine 1 during steady operation and the drive load on the driven device 5. For example, when the drive load is greater than the load on the engine 1 during steady operation, the drive control unit 624 causes the motor 41 to output a difference between the load on the engine 1 during steady operation and the drive load. Specifically, the drive control unit 624 controls the output current of the battery 42 to cause the battery 42 to supply power to the motor 41 so that the output of the motor 41 is equal to the difference. In this way, the drive control unit 624 can cause the engine 1 to operate steadily, even when the vehicle is traveling uphill or accelerating, and can maintain a constant exhaust temperature.

[0042] When the driving load is smaller than the load on the engine 1 during steady operation, the driving control unit 624 causes the motor 41 to function as a generator and causes the motor 41 to generate power in accordance with the difference between the load on the engine 1 during steady operation and the driving load. Specifically, the driving control unit 624 applies a load to the engine 1 according to the difference to cause the engine 1 to operate steadily, and causes the motor 41 to generate power according to the difference. In this way, by causing the motor 41 to function as a generator, the driving control unit 624 can cause the engine 1 to operate steadily without reducing the load on the engine 1.

[0043] [Process to set target value M] 5 is a flowchart showing an example of a process for setting the target value M. The process for setting the target value M is executed at predetermined intervals while the engine 1 is operating. The predetermined interval is, for example, 100 milliseconds, but is not limited to this.

[0044] The acquisition unit 621 acquires the remaining capacity SOC of the battery 42 (step S1). Specifically, the acquisition unit 621 acquires capacity information indicating the remaining capacity from a battery monitoring system that monitors the remaining capacity of the battery 42.

[0045] The setting unit 622 determines whether the remaining capacity SOC is equal to or greater than a threshold D (step S2). If the remaining capacity SOC is equal to or greater than the threshold D (Yes in step S2), the setting unit 622 sets a target value M according to the remaining capacity SOC (step S3).

[0046] The drive control unit 624 operates the engine 1 in a steady state so that the load on the engine 1 is constant (step S4). Specifically, the drive control unit 624 operates the engine 1 in a steady state so that the exhaust temperature is equal to or higher than the activation temperature E and equal to or lower than the upper limit temperature, and the load is constant.

[0047] The acquisition unit 621 acquires the difference between the load and the driving load of the engine 1 during steady operation (step S5). The driving control unit 624 determines whether the driving load is equal to or greater than the load (step S6). If the driving load is equal to or greater than the load (Yes in step S6), the driving control unit 624 causes the motor 41 to output the difference (step S7). Specifically, the driving control unit 624 controls the current applied to the motor 41 so that the output of the motor 41 is equal to the difference.

[0048] If the drive load is less than the load (No in step S6), the drive control unit 624 causes the motor 41 to generate power based on the difference (step S8). Specifically, the drive control unit 624 applies a load based on the difference to the engine 1 to cause the engine 1 to operate steadily, and causes the motor 41 to generate power based on the difference.

[0049] If the remaining capacity SOC is less than the threshold value D (No in step S2), the setting unit 622 sets the target value M to the lower limit target value C (step S9). The drive control unit 624 drives the engine 1 in accordance with the drive load (step S10).

[0050] [Effects of Purification System S] As explained above, the purification system S according to the embodiment includes the engine 1, the catalyst 21 that purifies the exhaust gas by causing a reaction between the adsorbed ammonia and nitrogen oxides contained in the exhaust gas of the engine 1, the motor 41 that drives to compensate for the difference between the load on the engine 1 and the drive load of the driven device 5 driven by the engine 1, and the battery 42 that supplies power to the motor 41. The purification system S increases the target value M of the amount of ammonia adsorbed on the catalyst 21 as the remaining capacity of the battery 42 increases.

[0051] With the above configuration, the purification system S of the present invention can increase the amount of ammonia adsorbed by the catalyst 21 as the remaining capacity of the battery 42 increases. Furthermore, the purification system S compensates for the difference between the drive load and the load of the engine 1 using the motor 41 driven by the battery 42, thereby suppressing load fluctuations on the engine 1. As a result, the purification system S can suppress an increase in the exhaust temperature of the engine 1, so that even if the amount of ammonia adsorbed by the catalyst 21 is increased, the emission of ammonia to the outside can be suppressed. Furthermore, since the amount of ammonia adsorbed by the catalyst 21 increases, nitrogen oxides and ammonia react more easily on the catalyst 21. As a result, the purification rate of the exhaust gas is improved. In this way, the purification system S can achieve both purification of the exhaust gas rate and suppression of ammonia emissions into the atmosphere.

[0052] The present invention has been described above using embodiments, but the technical scope of the present invention is not limited to the scope described in the above embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. For example, all or part of the device can be configured by functionally or physically distributing or integrating any unit. Furthermore, new embodiments resulting from any combination of multiple embodiments are also included in the embodiments of the present invention. The effects of the new embodiments resulting from the combination also have the effects of the original embodiments. [Explanation of symbols]

[0053] 1 engine 2 Purification equipment 3 Urea injection part 5 Driven equipment 6. Control device 7 Sensors 11 Exhaust pipe 12 Output shaft 21 Catalyst 41 Motor 42 Battery 61 Storage section 62 Control Unit 200 Celsius 621 Acquisition Department 622 Settings 623 Injection control unit 624 Drive control unit S Purification System

Claims

1. The engine and a catalyst that purifies the exhaust gas by reacting the adsorbed ammonia with nitrogen oxides contained in the exhaust gas of the engine; a motor that assists the engine; a battery for supplying power to the motor; an injection control unit that controls an injection amount of urea so that the amount of ammonia adsorbed by the catalyst increases as the remaining capacity of the battery increases; A purification system having:

2. a setting unit that sets the target value of the amount of ammonia adsorbed by the catalyst so that the target value increases as the remaining capacity of the battery increases; The injection control unit injects the urea so that the adsorption amount of the ammonia becomes the target value. The purification system of claim 1 .

3. the setting unit sets the target value of the adsorption amount to a predetermined value when the remaining capacity is less than a threshold value. The purification system of claim 2 .

4. the setting unit sets the target value to an upper limit target value of the amount of ammonia that can be adsorbed by the catalyst when the remaining capacity is equal to or greater than a predetermined value and the exhaust temperature of the engine is equal to an activation temperature of the catalyst. The purification system according to claim 2 or 3.

5. the setting unit sets the upper limit target value to the target value when the target value determined according to the remaining capacity is greater than the limit amount of the adsorption amount determined according to the exhaust temperature. The purification system of claim 4.

6. a drive control unit that operates the engine in a steady state so that the exhaust temperature of the engine is equal to or higher than the activation temperature of the catalyst and the load of the engine is constant; The purification system according to any one of claims 1 to 3.

7. The drive control unit When a driving load of a driven device driven by the engine is greater than the load of the engine during the steady operation, a difference between the load of the engine during the steady operation and the driving load is output to the motor; When the driving load is smaller than the load of the engine during the steady operation, the motor is caused to function as a generator and generate electricity using the difference. The purification system of claim 6.

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