JP7393098B2 - Exhaust purification system - Google Patents

Description

The present invention relates to a system for purifying exhaust gas from an internal combustion engine.

Japanese Patent Application Publication No. 2001-295634 discloses a system for purifying exhaust gas from an internal combustion engine. This conventional system includes a three-way catalyst and a power supply. The power supply device applies a voltage between electrodes attached to the three-way catalyst to generate a discharge limit electric field. The discharge limit electric field is the intensity of the electric field at which most of the gas molecules contained in the exhaust gas begin to dissociate.

When the ambient temperature of the three-way catalyst is lower than the appropriate temperature range, the potential energy of the gas molecules is low, and the purification reaction of the gas molecules by the three-way catalyst is difficult to proceed. In this regard, according to the conventional system, an increase in potential energy due to the discharge limit electric field is expected. Therefore, even when the ambient temperature is lower than the appropriate temperature range, the purification reaction can proceed in the same way as when the ambient temperature is within the appropriate temperature range.

Japanese Patent Application Publication No. 2001-295634 JP2013-209921A Japanese Patent Application Publication No. 2001-159309

However, the discharge limit electric field is assumed to have an intensity of several hundred kV/cm, and constantly generating the discharge limit electric field leads to wasted power. Further, generating a discharge limit electric field when the ambient temperature is within a proper temperature range also leads to wasted power. Therefore, improvements are desired that take into account the atmosphere of the three-way catalyst.

One object of the present invention is to reduce power consumption associated with the generation of an electric field in a system that purifies exhaust gas from an internal combustion engine by applying an electric field to a catalyst.

The present invention is an exhaust purification system that solves the above problems, and has the following features.
The exhaust gas purification system includes a purification catalyst, first and second electrodes, an acquisition device, and a power supply device.
The purification catalyst is provided in an exhaust pipe of an internal combustion engine.
The first and second electrodes are provided on the purification catalyst.
The acquisition device acquires a temperature of exhaust gas flowing into the purification catalyst .
The power supply device performs voltage control. In the voltage control , a voltage is applied to the first or second electrode so that a purification potential difference is generated between the first and second electrodes and an electric field is applied near the surface of the purification catalyst. is applied.
In the voltage control , the power supply device includes :
When the exhaust gas temperature is not between the lower temperature limit and the upper temperature limit set based on the lower limit or upper limit of the purification rate of exhaust components by the purification catalyst, the voltage is applied to the first or second electrode. Set the voltage command value to zero,
When the exhaust gas temperature is between the temperature lower limit value and the temperature upper limit value, a command value of the voltage to be applied to the first or second electrode is set such that the purification potential difference becomes smaller as the exhaust gas temperature increases. do .

According to the present invention , a voltage is applied to one of these electrodes such that a purification potential difference is generated between the first and second electrodes and an electric field is applied near the surface of the purification catalyst. Pressure control is performed. However, in voltage control, if the exhaust gas temperature is not between the temperature lower limit value and the temperature upper limit value, the command value of the applied voltage is set to zero. Therefore, it is possible to reduce power consumption compared to the case where voltage is constantly applied.

On the other hand, in voltage control, when the exhaust gas temperature is between the temperature lower limit value and the temperature upper limit value, the command value of the applied voltage is set so that the purification potential difference becomes smaller as the exhaust gas temperature becomes higher . When the command value of the applied voltage is set so that the purification potential difference is small, the amount of power consumed is less than when the command value is set so that the purification potential difference is kept constant. Therefore, it becomes possible to reduce power consumption associated with voltage application.

FIG. 1 is a diagram illustrating a configuration example of an exhaust gas purification system according to an embodiment. 7 is a flowchart illustrating a first voltage control processing example. 12 is a flowchart illustrating a second voltage control processing example. 12 is a flowchart illustrating a third voltage control processing example. FIG. 3 is a diagram illustrating a first setting example of a first potential difference. FIG. 7 is a diagram illustrating a second setting example of the first potential difference. FIG. 7 is a diagram illustrating a third setting example of the first potential difference. FIG. 7 is a diagram illustrating a first setting example of a second potential difference. FIG. 7 is a diagram illustrating a second setting example of a second potential difference. FIG. 7 is a diagram illustrating a third setting example of the second potential difference. FIG. 7 is a diagram illustrating a first setting example of a third potential difference. FIG. 7 is a diagram illustrating a second setting example of a third potential difference. FIG. 7 is a diagram illustrating a third setting example of a third potential difference.

Embodiments of the present invention will be described below with reference to the drawings. However, in the embodiments shown below, when referring to the number, amount, amount, range, etc. of each element, unless it is specifically specified or it is clearly specified to that number in principle, such reference shall be made. The present invention is not limited to this number. Further, the structures, steps, etc. described in the embodiments shown below are not necessarily essential to the present invention, unless specifically specified or clearly specified in principle.

1. System Configuration FIG. 1 is a diagram illustrating a configuration example of an exhaust gas purification system according to an embodiment of the present invention. The exhaust gas purification system 1 shown in FIG. 1 is mounted on a vehicle. The exhaust purification system 1 includes an internal combustion engine 10 as a power source for the vehicle. Examples of the internal combustion engine 10 include a diesel engine and a gasoline engine.

Internal combustion engine 10 includes an exhaust pipe 20 . Exhaust gas from the internal combustion engine 10 flows through the exhaust pipe 20 . A catalyst device 30 is provided in the middle of the exhaust pipe 20. The catalyst device 30 is a device that purifies harmful components (for example, hydrocarbons, carbon monoxide, and nitrogen oxides; hereinafter referred to as "exhaust components") contained in exhaust gas. The catalyst device 30 includes a catalyst 32, a first electrode 34, and a second electrode 36.

Examples of the catalyst 32 include an oxidation catalyst, a reduction catalyst, and a three-way catalyst. The oxidation catalyst promotes the oxidation reaction of exhaust components. The reduction catalyst promotes the reduction reaction of exhaust components. Three-way catalysts promote oxidation and reduction reactions simultaneously. A first electrode 34 and a second electrode 36 are attached to the catalyst 32. When a potential difference occurs between the first electrode 34 and the second electrode 36, an electric field is applied near the surface of the catalyst 32. The potential difference is generated by applying a voltage to the first electrode 34 or the second electrode 36.

The exhaust purification system 1 further includes a power supply device 40 and an acquisition device 50. The power supply device 40 includes a DC power supply 42, a control circuit 44, and a controller 46. The DC power supply 42 is a low voltage DC power supply of about 100V. The control circuit 44 applies a voltage to the first electrode 34 or the second electrode 36. Controller 46 is a microcomputer with at least one memory and at least one processor. The controller 46 outputs a voltage command value to be applied to the first electrode 34 or the second electrode 36 (hereinafter referred to as "applied voltage command value") to the control circuit 44 based on the signal from the acquisition device 50. do.

The acquisition device 50 is connected to the input side of the controller 46 . The acquisition device 50 acquires a physical quantity that has a correlation with the purification rate of exhaust components by the catalyst 32 (hereinafter also referred to as a "correlated physical quantity"). Examples of correlated physical quantities include exhaust temperature T, exhaust flow rate F, and exhaust air-fuel ratio λ. The exhaust gas temperature T is the temperature of the exhaust gas flowing into the catalyst 32. The exhaust flow rate F is the flow rate of exhaust gas flowing into the catalyst 32. The exhaust air-fuel ratio λ is the air-fuel ratio of the exhaust gas flowing into the catalyst 32. The acquisition device 50 acquires correlated physical quantities directly or indirectly.

2. Example of Voltage Control In this embodiment, the controller 46 performs first, second, or third voltage control. The first voltage control is performed based on the exhaust temperature T. The second voltage control is performed based on the exhaust flow rate F. The third voltage control is performed based on the exhaust air-fuel ratio λ. The first, second, or third voltage control is realized by the processor of the controller 46 reading a predetermined program from the memory and executing it.

2.1 First Voltage Control FIG. 2 is a flowchart illustrating a processing example of the first voltage control. The routine shown in FIG. 2 is executed at predetermined control intervals while the internal combustion engine 10 is operating.

In the routine shown in FIG. 2, first, the exhaust gas temperature T is acquired (step S10). Subsequently, it is determined whether the exhaust gas temperature T is between the lower limit value Tell and the upper limit value Telh (step S12). The lower limit value Tell and the upper limit value Telh are temperatures set based on experiments and the like based on the purification rate of exhaust components by the catalyst 32. The lower limit value Tell and the upper limit value Telh are set based on the lower limit value Rl or the upper limit value Rh of the purification rate. Both the lower limit value Rl and the upper limit value Rh are constant values.

If the determination result in step S12 is negative, the routine shown in FIG. 2 ends. That is, if the determination result in step S12 is negative, the first voltage control is not performed. On the other hand, if the determination result in step S12 is positive, the command value V1 of the applied voltage is output (step S14). The command value V1 is a potential that generates a first potential difference PD (Potential Difference) 1 for purification between the first electrode 34 and the second electrode 36.

2.2 Second Voltage Control FIG. 3 is a flowchart illustrating a processing example of the second voltage control. The routine shown in FIG. 3 is executed at predetermined control intervals while the internal combustion engine 10 is operating.

In the routine shown in FIG. 3, first, the exhaust flow rate F is acquired (step S20). Subsequently, it is determined whether the exhaust flow rate F is between the lower limit value Fell and the upper limit value Felh (step S22). The lower limit value Fell and the upper limit value Felh are temperatures set based on experiments and the like based on the purification rate of exhaust components by the catalyst 32. The lower limit value Fell and the upper limit value Felh are set based on the lower limit value Rl or the upper limit value Rh.

If the determination result in step S22 is negative, the routine shown in FIG. 3 ends. That is, if the determination result in step S22 is negative, the second voltage control is not performed. On the other hand, if the determination result in step S22 is positive, the command value V2 of the applied voltage is output (step S24). The command value V2 is a potential that generates a second potential difference PD2 for purification between the first electrode 34 and the second electrode 36.

2.3 Third Voltage Control FIG. 4 is a flowchart illustrating a processing example of the third voltage control. The routine shown in FIG. 4 is executed at predetermined control intervals while the internal combustion engine 10 is operating.

In the routine shown in FIG. 4, first, the exhaust air-fuel ratio λ is obtained (step S30). Subsequently, it is determined whether the exhaust air-fuel ratio λ is between the lower limit value λell and the upper limit value λelh (step S32). The lower limit value λell and the upper limit value λelh are temperatures set based on experiments and the like based on the purification rate of exhaust components by the catalyst 32. The lower limit value λell and the upper limit value λelh are set based on the lower limit value Rl or the upper limit value Rh.

If the determination result in step S32 is negative, the routine shown in FIG. 4 ends. That is, if the determination result in step S32 is negative, the third voltage control is not performed. On the other hand, if the determination result in step S32 is positive, the command value V3 of the applied voltage is output (step S34). The command value V3 is a potential that generates a third potential difference PD3 for purification between the first electrode 34 and the second electrode 36.

2.4 Effects of First to Third Voltage Controls When the first voltage control is performed, a first potential difference PD1 is generated between the first electrode 34 and the second electrode 36. When the first potential difference PD1 occurs, an electric field is generated between the first electrode 34 and the second electrode 36, and the potential energy of the exhaust component increases. Therefore, the purification reaction of exhaust components by the catalyst 32 is promoted. This promoting effect is also expected when the second voltage control that produces the second potential difference PD2 is performed, and is also expected when the third voltage control that produces the third potential difference PD3 is performed.

Further, the first, second, or third voltage control is not performed when the correlated physical quantity is outside the respective range. Therefore, it is possible to cancel the execution of voltage control when the above-mentioned promotion effect is not expected, thereby reducing wasted power.

3. Another example of voltage control In this embodiment, the controller 46 performs fourth, fifth, or sixth voltage control. The fourth, fifth, and sixth voltage controls are common to the first, second, and third voltage controls in the correlated physical quantity of interest. That is, the fourth voltage control is performed by focusing on the exhaust gas temperature T, which is common to the first voltage control. The fifth voltage control is performed by focusing on the exhaust flow rate F, which is common to the second voltage control. The sixth voltage control is performed by focusing on the exhaust air-fuel ratio λ, which is common to the third voltage control. The fourth, fifth, or sixth voltage control is realized by the processor of the controller 46 reading a predetermined program from the memory and executing it.

3.1 Fourth Voltage Control In the fourth voltage control, the first potential difference PD1 is set according to the exhaust temperature T. FIG. 5 is a diagram illustrating a first setting example of the first potential difference PD1. In this first example, when the exhaust temperature T is the upper limit value Telh, the first potential difference PD1 is set to PD11, and when the exhaust temperature T is the lower limit value Tell, the first potential difference PD1 is set to PD12 (<PD11). Further, when the exhaust gas temperature T is between the upper limit value Telh and the lower limit value Tell, the first potential difference PD1 is set to a smaller value as the exhaust gas temperature T becomes higher.

As described in the definition of the correlated physical quantities, the exhaust gas temperature T has a correlation with the purification rate of exhaust components by the catalyst 32. The reason for this is that there is a correlation between the potential energy of the exhaust component and the exhaust temperature T. Specifically, the higher the exhaust gas temperature T, the more the potential energy of the exhaust components increases. From this, it can be seen that as the exhaust gas temperature T becomes higher, less activation energy is required for the progress of the purification reaction of the exhaust gas components. The fourth voltage control focuses on such a relationship. Note that the command value V1 output to the control circuit 44 is changed as appropriate depending on the set first potential difference PD1.

6 and 7 are diagrams illustrating second and third setting examples of the first potential difference PD1. In the first setting example described with reference to FIG. 5, the first potential difference PD1 is expressed by a linear function with the exhaust gas temperature T as a variable. In the second setting example shown in FIG. 6, the first potential difference PD1 is expressed by a downwardly convex function. In the third setting example shown in FIG. 7, the first potential difference PD1 is expressed by an upwardly convex function.

3.2 Fifth Voltage Control In the fifth voltage control, the second potential difference PD2 is set according to the exhaust flow rate F. FIG. 8 is a diagram illustrating a first setting example of the second potential difference PD2. In this first example, when the exhaust flow rate F is the lower limit value Fell, the second potential difference PD2 is set to PD21, and when the exhaust flow rate F is the upper limit value Felh, the second potential difference PD2 is set to PD22 (>PD21). Further, when the exhaust flow rate F is between the upper limit value Felh and the lower limit value Fell, the second potential difference PD2 is set to a smaller value as the exhaust flow rate F decreases.

As described in the definition of the correlated physical quantities, the exhaust flow rate F has a correlation with the purification rate of exhaust components by the catalyst 32. The reason for this is that there is a correlation between the amount of exhaust components diffused into the structure of the catalyst 32 and the exhaust flow rate F. Specifically, as the exhaust flow rate F decreases, the amount of exhaust components that diffuse into the catalyst 32 increases. An increase in the amount of diffusion means that the opportunity for the catalyst 32 to purify exhaust components increases. From this, it can be seen that the smaller the exhaust flow rate F is, the easier the purification reaction of exhaust components is to proceed. The fifth voltage control focuses on such a relationship. Note that the command value V2 output to the control circuit 44 is changed as appropriate according to the second potential difference PD2 after setting.

9 and 10 are diagrams illustrating second and third setting examples of the second potential difference PD2. In the first setting example described with reference to FIG. 8, the second potential difference PD2 is expressed by a linear function with the exhaust flow rate F as a variable. In the second setting example shown in FIG. 9, the second potential difference PD2 is expressed by a downwardly convex function. In the third setting example shown in FIG. 10, the second potential difference PD2 is expressed by an upwardly convex function.

3.3 Sixth Voltage Control In the sixth voltage control, the third potential difference PD3 is set according to the exhaust air-fuel ratio λ. FIG. 11 is a diagram illustrating a first setting example of the third potential difference PD3. In this first example, when the exhaust air-fuel ratio λ is the predetermined air-fuel ratio λr, the third potential difference PD3 is set to PD31. Further, when the exhaust air-fuel ratio λ is the upper limit value λelh and the lower limit value λell, the third potential difference PD3 is set to PD32 (>PD31). Note that the third potential difference PD3 at the upper limit value λelh and that at the lower limit value λell may be set to different values.

Further, when the exhaust air-fuel ratio λ is between the predetermined air-fuel ratio λr and the upper limit value λelh, the third potential difference PD3 is set to a smaller value as the exhaust air-fuel ratio λ becomes smaller. When the exhaust air-fuel ratio λ is between the predetermined air-fuel ratio λr and the lower limit value λell, the third potential difference PD3 is set to a smaller value as the exhaust air-fuel ratio λ becomes larger. Note that the predetermined air-fuel ratio λr may be set to a constant value, or may be individually set to a value depending on the exhaust component of interest.

As described in the definition of the correlated physical quantity, the exhaust air-fuel ratio λ has a correlation with the purification rate of exhaust components by the catalyst 32. The reason for this is that the closer the exhaust air-fuel ratio λ is to the predetermined air-fuel ratio λr, the better the reaction conditions are for the purification reaction of exhaust components to proceed more easily. From this, it can be seen that the smaller the difference between the exhaust air-fuel ratio λ and the predetermined air-fuel ratio λr, the easier the purification reaction of the exhaust components will proceed. The sixth voltage control focuses on such a relationship. Note that the command value V3 output to the control circuit 44 is appropriately changed according to the third potential difference PD3 after setting.

FIGS. 12 and 13 are diagrams illustrating second and third setting examples of the third potential difference PD3. In the first setting example described with reference to FIG. 11, the third potential difference PD3 is expressed by a linear function using the exhaust air-fuel ratio λ as a variable. In the second setting example shown in FIG. 12, the third potential difference PD3 is expressed by two types of downwardly convex functions with the predetermined air-fuel ratio λr as the boundary. In the third setting example shown in FIG. 13, the third potential difference PD3 is expressed by an upwardly convex function with the predetermined air-fuel ratio λr as the boundary.

3.4 Effects of Fourth to Sixth Voltage Controls When the fourth voltage control is performed, the first potential difference PD1 is set to a smaller value as the exhaust gas temperature T becomes higher. When the fifth voltage control is performed, the second potential difference PD2 is set to a smaller value as the exhaust flow rate F decreases. When the sixth voltage control is performed, the third potential difference PD3 is set to a smaller value as the exhaust air-fuel ratio λ approaches the predetermined air-fuel ratio λr. In other words, no matter which voltage control is performed, the potential difference for purification is set to a small value under conditions in which the purification reaction of exhaust components is likely to proceed. The fact that the potential difference for purification is set to a small value means that the amount of power consumed is less than when the same potential difference is set to a constant value. Therefore, it becomes possible to reduce power consumption associated with execution of voltage control.

1 Exhaust purification system 10 Internal combustion engine 20 Exhaust pipe 30 Catalyst device 32 Catalyst 34 First electrode 36 Second electrode 40 Power supply device 42 DC power supply 44 Control circuit 46 Controller 50 Acquisition device

Claims (1)

A purification catalyst installed in the exhaust pipe of an internal combustion engine,
first and second electrodes provided on the purification catalyst;
an acquisition device that acquires the temperature of the exhaust gas flowing into the purification catalyst ;
Voltage control is performed to apply a voltage to the first or second electrode so that a purification potential difference is generated between the first and second electrodes and an electric field is applied near the surface of the purification catalyst. a power supply;
Equipped with
In the voltage control , the power supply device includes :
When the exhaust gas temperature is not between the lower temperature limit and the upper temperature limit set based on the lower limit or upper limit of the purification rate of exhaust components by the purification catalyst, the voltage is applied to the first or second electrode. Set the voltage command value to zero,
When the exhaust gas temperature is between the temperature lower limit value and the temperature upper limit value, a command value of the voltage to be applied to the first or second electrode is set such that the purification potential difference becomes smaller as the exhaust gas temperature increases. do
An exhaust purification system characterized by:

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