Exhaust gas purification system for vehicle

Abstract

A vehicle exhaust gas purification system and a control method thereof that may effectively remove nitrogen oxides in an exhaust gas even in a cold state, which is the initial stage of an engine starting, is disclosed. A control method of an exhaust gas purification system of a vehicle may include: a step of performing a rich control for controlling a concentration of non-combusted fuel contained in the exhaust gas flowing into the housing to be a rich fuel directly after the starting of the engine; a step of performing a lean control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing to be a lean fuel; a step of determining whether a temperature of the exhaust gas flowing into the housing is a predetermined temperature or more; and a step of performing a normal control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing so that a lean fuel and a rich fuel are periodically repeated with a regular interval.

Claims

1. An exhaust gas purification system of a vehicle provided on an exhaust pipe connected to an exhaust side of an engine for purifying an exhaust gas of the engine, comprising: a housing having a front and a rear, the housing configured to receive the exhaust gas exhausted from the engine and disposed on the exhaust pipe to exhaust the exhaust gas downstream of the housing; a front catalyst embedded in the housing to primarily purify the exhaust gas flowing into the housing through the front of the housing; a rear catalyst embedded in the housing to secondarily purify the exhaust gas passing through the front catalyst before flowing out to the rear of the housing; and a controller connected to the exhaust pipe via a temperature sensor at the front of the housing and configured to control a concentration of a non-combusted fuel included in the exhaust gas according to a temperature of the exhaust gas flowing into the housing, wherein the temperature of the exhaust gas flowing into the housing is detected by the temperature sensor disposed at the front of the housing, and wherein the controller is configured to temporarily perform a rich control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing to be a rich fuel at a lambda value of less than 0.9 for a predetermined time when the temperature of the exhaust gas flowing into the housing is less than a predetermined temperature, and further configured to subsequently perform a lean control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing to be a lean fuel at a lambda value of greater than 1.02 after the rich control until the temperature of the exhaust gas flowing into the housing reaches the predetermined temperature.

2. The exhaust gas purification system of the vehicle of claim 1, wherein the front catalyst is a palladium catalyst oxidizing hydrocarbons and carbon monoxide and simultaneously occluding nitrogen oxides.

3. The exhaust gas purification system of the vehicle of claim 2, wherein the front catalyst is a Pd/CZO catalyst.

4. The exhaust gas purification system of the vehicle of claim 1, wherein the rear catalyst is a rhodium catalyst reducing nitrogen oxides.

5. The exhaust gas purification system of the vehicle of claim 4, wherein the rear catalyst is a Rh/CZO catalyst.

6. The exhaust gas purification system of the vehicle of claim 1, wherein the controller is configured to perform a normal control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing so that a lean fuel and a rich fuel are periodically repeated with a regular interval when the temperature of the exhaust gas flowing into the housing is greater than or equal to the predetermined temperature.

7. The exhaust gas purification system of the vehicle of claim 1, wherein the predetermined time is more than 1 second.

8. A control method for controlling an exhaust gas purification system of a vehicle, in which a front catalyst to primarily purify an exhaust gas and a rear catalyst to secondarily purify the exhaust gas passing through the front catalyst are embedded in a housing configured to receive the exhaust gas exhausted from an engine and disposed on an exhaust pipe to exhaust the exhaust gas downstream of the housing and a concentration of a non-combusted fuel contained in the exhaust gas is controlled according to a temperature of the exhaust gas flowing into the housing by a controller, comprising the steps of: performing, by the controller, a rich control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing to be a rich fuel at a lambda value of less than 0.9 for a predetermined time directly after starting of the engine; subsequently performing, by the controller, a lean control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing to be a lean fuel at a lambda value of greater than 1.02 after the rich control; determining, by the controller, whether the temperature of the exhaust gas flowing into the housing is a predetermined temperature or more; and performing, by the controller, a normal control for controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing so that a lean fuel and a rich fuel are periodically repeated with a regular interval in response to determining that the temperature of the exhaust gas flowing into the housing is equal to or greater than the predetermined temperature.

9. The control method of the exhaust gas purification system of the vehicle of claim 8, wherein the predetermined time is more than 1 second and the front catalyst is reduced for the predetermined time.

10. The control method of the exhaust gas purification system of the vehicle of claim 8, wherein whether the temperature of the exhaust gas flowing into the housing is the predetermined temperature or more is continuously determined while the lean control is performed.

11. The control method of the exhaust gas purification system of the vehicle of claim 8, wherein the control method is finished when performing the normal control.

12. The control method of the exhaust gas purification system of the vehicle of claim 8, wherein the front catalyst is a palladium catalyst oxidizing hydrocarbons and carbon monoxide and simultaneously occluding nitrogen oxides, the rear catalyst is a rhodium catalyst reducing nitrogen oxides, the nitrogen oxides are occluded to the front catalyst while the lean control is performed in a state wherein the temperature of the exhaust gas flowing into the housing is less than the predetermined temperature after the rich control is performed, and nitrogen oxides are separated from the front catalyst and reduced in the rear catalyst while the temperature of the exhaust gas flowing into the housing is the predetermined temperature or more such that the normal control is performed.

Description

DRAWINGS

(1) In order that the disclosure may be well understood, there will now be described various forms thereof, given by way of example, reference being made to the accompanying drawings, in which:

(2) FIG. 1 is a schematic diagram of an exhaust gas purification system of a vehicle according to one form of the present disclosure;

(3) FIG. 2 is a schematic diagram of a variation of an exhaust gas purification system of a vehicle according to another form of the present disclosure;

(4) FIG. 3 is a graph showing performance of storing nitrogen oxides when an exhaust gas purification system of a vehicle according to one form of the present disclosure is operated without a temporary rich control in a cold state of an engine;

(5) FIG. 4 is a graph showing a performance of storing nitrogen oxides when an exhaust gas purification system of a vehicle according to one form of the present disclosure is operated through a temporary rich control in a cold state of an engine;

(6) FIG. 5 is a block diagram illustrating a relationship of inputs and outputs for performing a control method of an exhaust gas purification system of a vehicle according to a form of the present disclosure; and

(7) FIG. 6 is a flowchart of a control method of an exhaust gas purification system of a vehicle according to a form of the present disclosure.

(8) The drawings described herein are for illustration purposes only and are not intended to limit the scope of the present disclosure in any way.

DETAILED DESCRIPTION

(9) The following description is merely exemplary in nature and is not intended to limit the present disclosure, application, or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features.

(10) Aspects of the present disclosure will hereinafter be described in detail with reference to the accompanying drawings.

(11) FIG. 1 is a schematic diagram of an exhaust gas purification system of a vehicle according to one form of the present disclosure.

(12) As shown in FIG. 1, an exhaust gas purification system 20 of a vehicle may be provided on an exhaust pipe 12 for purifying an exhaust gas of an engine 10. The engine 10 is equipped with at least one combustion chamber 31, and an injector 32 is mounted in each combustion chamber 31 to inject a fuel thereinto. The combustion chamber 31 is fluidly connected to an intake pipe 33 such that an air is supplied into the combustion chamber 31 through the intake pipe 33. An air flowmeter 34 is mounted at the intake pipe 33 to detect a flow rate of the air flowing through the intake pipe 33. In addition, the combustion chamber 31 is fluidly connected to the exhaust pipe 12 such that the exhaust gas is discharged out of the combustion chamber 31 through the exhaust pipe 12. A temperature sensor 35 is mounted at the exhaust pipe 12 to detect a temperature of the exhaust gas flowing through the exhaust pipe 12.

(13) The exhaust gas purification system 20 includes a front catalyst 22 and a rear catalyst 24 in a housing 21. FIG. 1 shows a part of the housing 21 that is cut to show a configuration of the front catalyst 22 and the rear catalyst 24.

(14) The exhaust pipe 12 is connected with the exhaust side of the engine 10 to exhaust the exhaust gas exhausted from the engine 10 to the outside. Meanwhile, the exhaust pipe 12 may extend rearward along an under floor of the vehicle to exhaust the exhaust gas to the rear of the vehicle, and the arrangement of the exhaust pipe 12 and the connection of the exhaust pipe 12 to the exhaust side of the engine 10 is obvious to a person skilled in the art, so a detailed description thereof is omitted.

(15) The exhaust gas exhausted from the engine 10 passes through the exhaust pipe 12 via the exhaust gas purification system 20. The exhaust gas via the exhaust gas purification system 20 sequentially passes through the front catalyst 22 and the rear catalyst 24. In other words, the front end of the housing 21 is connected to the engine 10 by the exhaust pipe 12 to receive the exhaust gas exhausted from the engine 10, and the rear end of the housing 21 communicates with the exhaust pipe 12 to exhaust the exhaust gas via the exhaust gas purification system 20 to the rear of the vehicle. Here, the front and rear of the constituent elements is based on the flow of the exhaust gas, and it is defined that the exhaust gas flows from the front to the rear of the constituent elements.

(16) The front catalyst 22 functions to primarily purify the exhaust gas that is flowing into the housing 21 through the front of the housing 21.

(17) Also, the front catalyst 22 is a palladium catalyst, and oxidizes hydrocarbons (HC) and carbon monoxide (CO) and simultaneously occludes nitrogen oxides (NOx). More specifically, a Pd/CZO catalyst among the palladium (Pd) catalyst may be applied to the front catalyst 22. Here, since the Pd catalyst and CZO, which is a mixed oxide of cerium (Ce) and zirconium (Zr) contained in order to increase the activity efficiency of the Pd catalyst, are obvious to a person of ordinary skill in the art, a detailed description thereof is omitted.

(18) The rear catalyst 24 is disposed at the rear of the front catalyst 22, and functions to secondarily purify the exhaust gas having passed the front catalyst 22 before being discharged to the rear end of the housing 21. In addition, the rear catalyst 24 is a rhodium catalyst, which reduces nitrogen oxides (NOx). More specifically, a Rh/CZO catalyst among the rhodium (Rh) catalyst may be applied to the rear catalyst 24. The Rh catalyst is obvious to a person of ordinary skill in the art, so a detailed description thereof will be omitted.

(19) The exhaust gas purification system 20 further includes a controller 25.

(20) The controller 25 is connected to the air flowmeter 34 to receive a signal corresponding to the flow rate of the air flowing through the intake pipe 33 and is connected to the temperature sensor 35 to receive a signal corresponding to the temperature of the exhaust gas flowing in the exhaust pipe 12 connected to the front of the housing 21. The controller 25 is connected to the injector 32 to control the concentration of the non-combusted fuel contained in the exhaust gas. That is, the controller 25 functions to regulate the fuel concentration of the exhaust gas according to the temperature of the exhaust gas flowing into the housing 21. Here, for collecting the temperature of the exhaust gas and information of an air/fuel ratio by the controller 25, the temperature sensor 35 and an oxygen sensor (not shown) connected to the controller 25 are typically used, however it is not limited thereto. In addition, the controller 25 performs a normal control, a rich control, and a lean control according to the temperature of the exhaust gas flowing into the housing 21.

(21) The normal control of the controller 25 refers to controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing 21 so that the lean fuel and the rich fuel are periodically repeated with the regular interval. The normal control is performed when the temperature of the exhaust gas flowing into the housing 21 is above a predetermined temperature (T).

(22) The rich control of the controller 25 refers to controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing 21 to become the rich fuel. This rich control is selectively performed when the temperature of the exhaust gas flowing into the housing 21 is below the set temperature (T). Here, the predetermined temperature (T) is a temperature at which the cold state of the engine 10 is determined, and the controller 25 determines that the engine 10 is in a cold state at the initial stage of the engine startup if the temperature of the exhaust gas flowing into the housing 21 is less than the predetermined temperature (T).

(23) The lean control of the controller 25 refers to controlling the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing 21 to be a lean fuel. This lean control is selectively performed when the temperature of the exhaust gas flowing into the housing 21 is less than the predetermined temperature (T). Here, the lean control may be continuously performed after the rich control is temporarily executed in the cold state of the initial stage of the engine 10 startup. Also, the rich control may be performed temporarily while the engine 10 is starting, then the lean control may be performed while the cold state of the initial stage of the engine 10 starting is maintained, and the normal control may be performed when the engine 10 is out of the cold state of the initial starting.

(24) Further, the reference of the lean fuel and the rich fuel, the method of adjusting the air/fuel ratio so that the concentration of the non-combusted fuel contained in the exhaust gas flowing into the housing 21 is controlled as the lean fuel or the rich fuel, and the predetermined temperature (T) determining the cold state of the engine 10 may be selected according to a design of the engine and auxiliary components, and are obvious to a person of ordinary skill in the art.

(25) FIG. 2 is a schematic diagram of a variation of an exhaust gas purification system of a vehicle according to another aspect of the present disclosure.

(26) As shown in FIG. 2 (a), the front catalyst 22 to which the Pd/CZO catalyst is applied among the palladium (Pd) catalyst and the rear catalyst 24 to which the Rh/CZO catalyst is applied among the rhodium (Rh) catalyst may be coated to be overlapped on a carrier (not shown). In this case, as the front catalyst 22 is coated on the relative outer side with which the exhaust gas is in direct contact and the rear catalyst 24 is coated on the relative inner side close to the carrier, the function that the front catalyst 22 oxidizes hydrocarbons (HC) and carbon monoxide (CO) and simultaneously occludes nitrogen oxides (NOx) and the function that the rear catalyst 24 reduces the occluded nitrogen oxides (NOx), may be secured.

(27) As shown in FIG. 2 (b), the front catalyst 22 and the rear catalyst 24 may be provided so that the palladium (Pd) may be coated on the relative front to configure the front catalyst 22 and the rhodium (Rh) may be coated on the relative rear to configure the rear catalyst 24 on the CZO coated on the substrate. Thereby, the function that the front catalyst 22 oxidizes hydrocarbons (HC) and carbon monoxide (CO) and simultaneously occludes nitrogen oxides (NOx), and the function that the rear catalyst 24 reduces nitrogen oxides (NOx), are secured.

(28) As shown in FIG. 2 (c), the front catalyst 22 to which the Pd/CZO catalyst among the palladium (Pd) catalyst is applied and the rear catalyst 24 to which the Rh/CZO catalyst among the rhodium (Rh) catalyst is applied may be sequentially coated on the carrier. That is, the Pd/CZO catalyst may be coated on the relative front on the carrier and the Rh/CZO catalyst may be coated on the relative rear on the carrier. Thereby, the function that the front catalyst 22 oxidizes hydrocarbons (HC) and carbon monoxide (CO) and simultaneously occludes nitrogen oxides (NOx), and the function that the rear catalyst 24 reduces nitrogen oxides (NOx) are secured.

(29) The configuration according to the modified forms of the front catalyst 22 and the rear catalyst 24, which are coated to be overlapped or sequentially arranged on the carrier, may be selectively implemented according to the intention of a person of ordinary skill in the art.

(30) FIG. 3 is a graph showing performance of storing nitrogen oxides when an exhaust gas purification system of a vehicle according to an aspect of the present disclosure is operated without a temporary rich control in a cold state of an engine.

(31) In a graph G1 shown in FIG. 3, a vertical axis represents the concentration of nitrogen oxides (NOx) included in the exhaust gas and a horizontal axis represents time. That is, the graph G1 shows the concentration of nitrogen oxides (NOx) included in the exhaust gas according to time in the initial cold state after starting the engine 10. On the other hand, in the graph G1, an increasing curve of the temperature of the exhaust gas according to the time in the initial cold state after the starting of the engine 10 is shown by a dotted line, the change in the concentration (Inflow NOx) of nitrogen oxides (NOx) contained in the exhaust gas flowing into the housing 21 is shown by a one-dot chain line, and the change in the concentration (Outflow NOx) of nitrogen oxides (NOx) contained in the exhaust gas flowing out of the housing 21 is shown by a solid line.

(32) The change in the outflow NOx shown in the graph G1 is experimentally determined separate from the actual control of the exhaust gas purification system 20 of the vehicle according to one aspect of the present disclosure, and shows the change of the Outflow NOx according to the nitrogen oxides (NOx) occluding by the front catalyst 22, particularly, in the case that a precondition for performing the occluding of the nitrogen oxides (NOx) through the front catalyst 22 in the initial cold state after the starting of the engine 10 is the lean fuel condition under the normal control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21, so that the lean fuel and the rich fuel are periodically repeated at regular intervals. That is, the graph G1 is for helping to understand that the concentration (Outflow NOx) of nitrogen oxides (NOx) included in the exhaust gas flowing out from the housing 21 is remarkably different in the case that the precondition is the lean fuel condition compared with the case that the precondition for performing the occluding of nitrogen oxides (NOx) by the front catalyst 22 is temporarily made into the rich fuel condition through the rich control controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21 to be the rich fuel.

(33) FIG. 4 is a graph showing performance of storing nitrogen oxides when an exhaust gas purification system of a vehicle according to an aspect of the present disclosure is operated through a temporary rich control in a cold state of an engine.

(34) The graph G2 shown in FIG. 4 excludes the change of the Outflow NOx in the case that the precondition for performing the occluding of the nitrogen oxides (NOx) by the front catalyst 22 is the lean fuel condition in the graph G1 shown in FIG. 3, and shows the change of the Outflow NOx in the case that the precondition for performing the occluding of the nitrogen oxides (NOx) by the front catalyst 22 is made into the rich fuel condition through the rich control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21 to be the rich fuel. In other words, in the graph G2 shown in FIG. 4, the increasing curve of the temperature increase and the change of the Inflow NOx are the same as shown in FIG. 3, and the change of the Outflow NOx is different from in the graph G1 shown in FIG. 3. On the other hand, in the graph G2, the increasing curve of the temperature increase according to the time passage in the initial cold state after the starting of the engine 10 is shown by a dotted line, the change in the concentration (Inflow NOx) of nitrogen oxides (NOx) contained in the exhaust gas flowing into the housing 21 is shown by a one-dot chain line, and the change of the concentration (Outflow NOx) of nitrogen oxides (NOx) included in the exhaust gas flowed out from the housing 21 is shown by a solid line. As shown in the Outflow NOx change in FIG. 3 and FIG. 4, in the initial cold state of the starting of the engine 10, if the precondition for performing the occluding of nitrogen oxides (NOx) by the front catalyst 22 is controlled to be the rich fuel so that the exhaust gas flowing into the housing 21 temporarily becomes the rich fuel, the concentration (Outflow NOx) of nitrogen oxides (NOx) included in the exhaust gas having flowed out from the housing 21 is remarkably reduced compared with the case that the precondition is the lean fuel. That is, a storing amount of nitrogen oxides (NOx) occluding nitrogen oxides (NOx) in the front catalyst 22 is greatly increased.

(35) In this way, in the rich control of the precondition for improving the occluding performance of nitrogen oxides (NOx) of the front catalyst 22, properties of the front catalyst 22, which the occluding amount of nitrogen oxides (NOx) after the Pd/CZO catalyst is reduced is increased, the occluding amount of nitrogen oxides (NOx) is increased in the state that the palladium (Pd) catalyst is a metal, the NO adsorbed on the Pd is surface-moved (spillover) to the adjacent CZO, and an absorbing force is increased while the NO surface-transferred to the CZO forms nitrites, etc. are used. On the other hand, the rich control of the precondition may be performed for 1 second to 3 seconds at a lambda value of 0.7 to 0.9. It may be desirable for the rich control of the precondition to last for more than 1 second at a peak lambda value of less than 0.9.

(36) FIG. 5 is a block diagram illustrating a relationship of inputs and outputs for performing a control method of an exhaust gas purification system of a vehicle according to a form of the present disclosure.

(37) As shown in FIG. 5, the controller 25 for performing a control method of an exhaust gas purification system of a vehicle according to one form of the present disclosure is connected to the air flowmeter 34 to receive the signal corresponding to the flow rate of the air supplied to the combustion chamber 31, and is connected to the temperature sensor 35 to receive the signal corresponding to the temperature of the exhaust gas flowing into the housing 21. In addition, the controller 25 is connected to the injector 32 to control the concentration of the non-combusted fuel contained in the exhaust gas according to the temperature of the exhaust gas flowing into the housing 21. The concentration of the non-corn busted fuel contained in the exhaust gas, which is not limited to, can be controlled by controlling an amount of the fuel supplied by the injector 32 according to the flow rate of the air supplied into the combustion chamber 31. To this end, the controller 25 may include a memory configured to store program instructions therein and a processor configured to execute the program instructions for performing steps of the method according to one form of the present disclosure.

(38) FIG. 6 is a flowchart of a control method of an exhaust gas purification system of a vehicle according to one form of the present disclosure.

(39) As shown in FIG. 6, a control method of the exhaust gas purification system of the vehicle according to an aspect of the present disclosure is started along with the starting of the engine 10 (S100). Also, the rich control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21 to be the rich fuel is performed by the controller 25 along with or directly after the starting of the engine 10 (S110). After temporarily performing the rich control to reduce the front catalyst 22, the lean control for controlling the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21 to be the lean fuel is performed by the controller 25 (S120). The lean control may be performed by maintaining the lambda value within 1.02˜1.1. The lean control may be preferably maintained until the lowest lambda value is 1.03 or more.

(40) The controller 25 determines whether the temperature of the exhaust gas flowing into the housing 21 is a predetermined temperature (T) or more during the lean control is performed (S130).

(41) If the temperature of the exhaust gas flowing into the housing 21 is less than the predetermined temperature (T), the lean control is continuously performed (S120). That is, the lean control is maintained when it is determined that the engine 10 is in the initial cold state of the starting.

(42) If the temperature of the exhaust gas flowing into the housing 21 is the predetermined temperature (T) or more, the normal control for the concentration of the non-combusted fuel included in the exhaust gas flowing into the housing 21 is performed by the controller 25 so that the lean fuel and the rich fuel are periodically repeated with the regular interval (S140). That is, the normal control is performed while the engine 10 is out of the initial cold state of the starting, and the control method of the exhaust gas purification system of the vehicle according to an aspect of the present disclosure for improving the efficiency of the front catalyst 22 occluding nitrogen oxides (NOx) in the initial cold state of the starting of the engine 10 while performing the normal control is finished (S150). Here, nitrogen oxides (NOx) are occluded to the front catalyst 22 while the lean control is performed by the controller 25 (S120) after the rich control is performed by the controller 25 (S110), nitrogen oxides (NOx) exit the front catalyst 22 and are reduced in the rear catalyst 24 to be removed while the temperature of the exhaust gas flowing into the housing 21 becomes the predetermined temperature (T) or more (S130) such that the normal control is performed by the controller 25 (S140). Referring to FIG. 3 and FIG. 4, the time point at which the nitrogen oxides (NOx) are removed is shown as when the temperature of the exhaust gas flowing into the housing 21 is above the predetermined temperature (T).

(43) As described above, according to one form of the present disclosure, by temporarily performing the rich control for reducing the front catalyst 22 of the three-way catalyst (TWC), the amount of nitrogen oxides (NOx) occluded to the front catalyst 22 in the lean fuel state may be increased. Thus, even in the cold state, which is the initial stage of the engine 10 starting, nitrogen oxides (NOx) in the exhaust gas may be effectively removed.

(44) While this present disclosure has been described in connection with what is presently considered to be practical forms, it is to be understood that the present disclosure is not limited to the disclosed forms, but on the contrary, it is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the present disclosure.