Patent Application
20110146274
This invention relates to a method and system for regenerating a particulate filter provided to remove particulate matter from exhaust gas, specifically a method and system for regenerating a particulate filter by burning matter trapped on the particulate filter.
Most of automobiles using an internal combustion engine, such as a diesel engine or the like, are equipped with a particulate filter designed to clean up exhaust gas by trapping PM (particulate matter) in the exhaust gas. Particulate filters used in diesel engine automobiles are called DPFs, in particular. Since PM accumulated to a certain level clogs such DPFs, the DPFs are regenerated by burning PM by raising the temperature of exhaust gas (see Patent Document 1, for example).
As mentioned above, in order to regenerate particulate filters such as DPFs, raising the exhaust gas temperature, namely increasing heat contained in the exhaust gas by supplying fuel to the engine is required. However, for efficient operation of the engine, the amount of fuel supplied to the engine is controlled to meet a predetermined air-fuel ratio, so that increasing heat contained in the exhaust gas at optional times is difficult. Thus, generally, DPFs are regenerated during high-load operation of automobiles.
In the method of regenerating the particulate filter disclosed in Patent Document 1, the exhaust gas temperature is raised by determining fuel injection quantity on the basis of a target for exhaust temperature and regulating actual expansion ratio by an expansion ratio varying means. This allows the particulate filter regeneration not only in the automobile's high-load operation but over a wide range of operating conditions.
The particulate filter regeneration method disclosed in Patent Document 1, however, requires an expansion ratio varying means for regulating the actual expansion ratio of the engine, resulting in complicated configuration and difficulty of control. Further, if a turbocharger is arranged upstream of the particulate filter, the exhaust gas loses heat by doing work in the turbocharger, resulting in low efficiency. Further, burning of matter trapped on the DPF requires oxygen, but if fuel supply is increased without increasing intake air supplied to the engine, oxygen in the intake air is consumed in combustion of fuel, resulting in lack of oxygen to burn matter trapped on the DPF.
The present invention has been made to solve problems as mentioned above. The primary object of the present invention is to provide a method and system for regenerating a particulate filter, capable of efficiently supplying oxygen to the particulate filter and efficiently raising the temperature of exhaust gas with simple configuration.
The present invention provides a method of regenerating a particulate filter provided in an exhaust line of an internal combustion engine equipped with a turbocharger, by burning matter trapped on the particulate filter by raising the temperature of exhaust gas at times that the particulate filter requires regeneration, comprising: a first step of increasing the flow rate of compressed air without depending on the flow rate of exhaust gas flowing across a turbine of the turbocharger, and a second step of delivering part of the compressed air from a section of an intake line upstream of the internal combustion engine to a section of the exhaust line upstream of the particulate filter, bypassing the engine.
The method may further comprise a third step of performing regulation to reduce the energy loss that the exhaust gas suffers in the turbine. The third step may consist of opening a variable nozzle provided to make the turbocharger a variable displacement type, or opening a wastegate, for example.
The present invention further provides a system for regenerating a particulate filter provided in an exhaust line of an internal combustion engine equipped with a turbocharger, by burning matter trapped on the particulate filter by raising the temperature of exhaust gas at times that the particulate filter requires regeneration, comprising: an intake quantity regulation means capable of increasing the flow rate of compressed air without depending on the flow rate of exhaust gas flowing across a turbine of the turbocharger, a bypass line connecting a section of an intake line upstream of the internal combustion engine to a section of the exhaust line upstream of the particulate filter, a flow rate regulation valve regulating the flow rate in the bypass line, and a control means controlling the intake quantity regulation means and the flow rate regulation valve.
The intake quantity regulation means may consist of an electric motor connected to the turbocharger or an electric booster arranged upstream of the turbocharger, for example. It is desirable that the bypass line be connected to the exhaust line, immediately after the internal combustion engine or immediately before the particulate filter.
The turbocharger may include a turbine flow regulation means regulating the flow rate of exhaust gas entering the turbine, where the control means regulates the turbine flow regulation means to reduce the energy loss that the exhaust gas suffers in the turbine. The turbine flow regulation means may consist of a variable nozzle or a wastegate, for example, where the control means opens the variable nozzle or the wastegaste.
The method and system for regenerating a particulate filter according to the present invention can increase the amount of oxygen supplied to the particulate filter by increasing the flow rate of compressed air without depending on the flow rate of exhaust gas flowing across a turbine of a turbocharger, and delivering part of the compressed air to the particulate filter, bypassing the internal combustion engine, and thus, enables effective burning of matter trapped on the particulate filter. Particularly, if the compressed air bypassing the internal combustion engine is delivered to the exhaust line, immediately after the internal combustion engine, it can cause burning of unburned fuel, resulting in an increase in heat.
Further, regulation to reduce the energy loss that the exhaust gas suffers in the turbine, or in other words, regulation to reduce heat loss by reducing the work done by the exhaust gas in the turbine leads to an efficient rise in exhaust gas temperature.
Referring to
The particulate filter regeneration system according to the present invention shown in
The turbocharger 1 is a device which drives a compressor 1c by a turbine 1t extracting energy from exhaust gas, thereby delivering compressed air to the engine 2 to increase power output of the engine. The compressor 1c has an inlet connected to the intake line 6 conveying air taken in from the outside, and an outlet connected to the engine intake line 6e delivering compressed air to the engine 2. The engine intake line 6e may include an intercooler to cool the compressed air. The turbine 1t has an inlet connected to an engine exhaust line 3e conveying exhaust gas of the engine 2, and an outlet connected to an exhaust line 3 discharging the exhaust gas to the outside. The engine intake line 6e constitutes part of the intake line 6 and the engine exhaust line 3e constitutes part of the exhaust line 3.
The turbocharger 1 shown in
Further, while the turbine 1t is being forcibly driven by the electric motor 5, exhaust gas flows across the turbine it without doing work, which minimizes loss of heat (exhaust gas energy).
The engine 2 is, for example a diesel engine or a gasoline engine mounted on an automobile or the like. The respective amounts of compressed air and fuel supplied to the engine 2 are controlled depending on operating conditions. Such control is performed by an electronic control unit (ECU) installed on the automobile. The engine 2 is controlled by controlling air-fuel ratio (mass ratio between air and fuel). For example, in normal operation, by driving the compressor 1c by the turbine 1t driven by exhaust gas, compressed air is supplied to the engine 2, and fuel is supplied to the engine 2 to achieve demanded power output of the engine 2. The air-fuel ratio is sometimes controlled to a level close to a stoichiometric air-fuel ratio (ratio resulting in a reaction between fuel and oxygen in the air with no fuel or oxygen left over) in order to effectively activate exhaust gas clean-up catalysts, and sometimes controlled to a level higher than the stoichiometric air-fuel ratio (economic air-fuel ratio) in order to improve fuel economy and reduce toxic substances in the exhaust gas. The electronic control unit (ECU) also functions as a control means 9 in the regeneration system according to the present invention.
The particulate filter 4 is, for example a DPF for use on a diesel engine automobile. The particulate filter 4 is made of ceramic or the like and traps particulate matter (PM) in the exhaust gas. Since the PM accumulated to a certain level clogs the particulate filter 4, the particulate filter 4 requires to be regenerated by burning the PM by raising the temperature of exhaust gas. Active raising of the exhaust gas temperature is possible by increasing fuel supply to the engine 2. On the other hand, although the burning of PM requires oxygen, oxygen in the air is consumed in combustion in the engine 2, so that the exhaust gas has a lower oxygen concentration, compared with the air, resulting in low efficiency of burning the PM. Thus, in the present invention, the bypass line 7 is provided to be able to supply fresh air to the particulate filter 4. As shown in
The bypass line 7 connects the engine intake line 6e to the exhaust line 3 to extract part of the air compressed by the compressor 1c from the intake line, before the engine 2, and deliver it to the exhaust line, before the particulate filter 4, bypassing the engine 2. Thus, the bypass line can supply fresh air, i.e., air not experiencing combustion in the engine 2 to the particulate filter 4. The amount of air bypassing the engine is controlled by the flow rate regulation valve 8. The flow rate regulation valve 8 may be arranged midway in the bypass line 7 as shown in the drawing, or at a point at which the bypass line branches off the engine intake line 6e, or at a point at which the bypass line meets the exhaust line 3. Sometimes an exhaust gas clean-up catalytic converter removing toxic substances (mainly, hydrocarbons, carbon monoxide and nitrogen oxides) from the exhaust gas is arranged in the exhaust line 3. Such exhaust gas clean-up catalytic converter is mostly arranged upstream of the particulate filter 4. The bypass line 7 may meet the exhaust line 3 either upstream or downstream of the exhaust gas clean-up catalytic converter.
The control means 9 is actually the aforementioned electric control unit (ECU). The control means 9 is electrically connected to a fuel supply means of the engine 2 to supply fuel to the engine 2 so that the engine 2 has a desired air-fuel ratio. The control means 9 is also electrically connected to the electric motor 5 to control the electric motor, determining whether to drive or stop it and the revolving speed thereof. The control means 9 is further electrically connected to the flow rate regulation valve 8 to control the flow rate regulation valve 8, determining whether to open or close it and how much to open it. The control means 9 is furthermore electrically connected to the pressure sensor 4s fitted to the particulate filter 4 to monitor the back pressure exerted on the particulate filter 4 to determine when to start and when to terminate the regeneration of the particulate filter 4.
Next, the function of the above-described particulate filter regeneration system, or in other words, the particulate filter regeneration method according to the present invention will be described. The method of regenerating the particulate filter 4 according to the present invention is designed to regenerate the particulate filter 4 arranged in the exhaust line 3 of the engine 2 equipped with the turbocharger 1, by burning matter trapped on the particulate filter 4 by raising the temperature of exhaust gas at times that the particulate filter 4 requires regeneration, and comprises a first step of increasing the flow rate of compressed air without depending on the flow rate of exhaust gas flowing across the turbine 1t of the turbocharger 1, and a second step of delivering part of the compressed air from a section of the intake line upstream of the engine 2 (engine intake line 6e) to a section of the exhaust line 3 upstream of the particulate filter 4, bypassing the engine 2.
The control means 9 determines whether to start regeneration of the particulate filter 4 on the basis of the output of the pressure sensor 4s fitted to the particulate filter 4. Specifically, the control means 9 determines whether to start regeneration of the particulate filter 4 by comparing the pressure (back pressure) downstream of the particulate filter 4 with a preset threshold. Whether to start regeneration of the particulate filter 4 may be determined on the basis of the pressure downstream of the particulate filter 4 detected by a pressure sensor 4s arranged downstream of the particulate filter 4 in the exhaust line 3, or on the basis of how long the particulate filter 4 has been used, if a pressure sensor 4s is not provided.
In the first step, the electric motor 5 is driven according to an instruction from the control means 8. This can increase the flow rate of compressed air without depending on the flow rate of exhaust gas flowing across the turbine 1t. The drive motor 5 is controlled to be able to supply compressed air in the amount providing oxygen required to burn the PM trapped on the particulate filter 4, in addition to the compressed air required for combustion in the engine. If the temperature of exhaust gas is not high enough to regenerate the particulate filter 4, the heat contained in the exhaust gas can be increased by switching the target for air-fuel ratio control from an economic air-fuel ratio to a stoichiometric or a fuel-rich air-fuel ratio, or by increasing the amount of air taken into the engine 2, thereby raising the upper limit of fuel supply.
In the second step, the flow rate regulation valve 8 is opened according to an instruction from the control means 9. This allows part of compressed air to be delivered from the engine intake line 6e to the section of the exhaust line 3 upstream of the particulate filter 4, bypassing the engine. The degree to which the flow rate regulation valve 8 is opened is controlled to be able to extract compressed air in the amount providing oxygen required to burn the PM trapped on the particulate filter 4. Incidentally, since the pressure in the engine intake line 6a is normally higher than the pressure in the exhaust line 3, there is no need to provide a suction device such as a pump. However, if desired, a suction device such as a pump may be arranged in the bypass line 7 to actively force the compressed air to the exhaust line.
When the pressure (back pressure) downstream of the particulate filter 4 decreases below a preset criterion, it is determined that the regeneration of the particulate filter 4 should be terminated. The control means 9 determines to terminate the regeneration on the basis of the output of the pressure sensor 4s. Alternatively, the control means may determine to terminate the regeneration after a predetermined time of regeneration of the particulate filter 4, where the regeneration time is empirically or statistically determined, and the control means 9 measures elapsed time after the start of regeneration.
Next, other embodiments of particulate filter 4 regeneration system according to the present invention will be described.
In the second embodiment of the present invention shown in
In the third embodiment of the present invention shown in
Such variable displacement supercharge 1 can, by itself, cover a wide range of engine 2 operation and provide high supercharging efficiency. The term “variable nozzle 1” is used to encompass all the variable mechanisms which can make the turbocharger 1a variable displacement type, among which there are mechanisms using flaps or vanes, for example. Incidentally, in
As shown in
In the fourth embodiment of the present invention shown in
As shown in
In the fifth embodiment of the present invention shown in
In the sixth embodiment of the present invention shown in
The present invention is not limited to the above-described embodiments. It goes without saying that various modifications can be made without departing from the spirit and scope of the present invention. For example, in the fourth and fifth embodiments, the outlet of the bypass line 7 may be connected to the exhaust line at the position taken in the second embodiment, and in the sixth embodiment, the outlet of the bypass line 7 may be connected to the exhaust line at the position taken in the first embodiment. Various features in the embodiments may be combined appropriately.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2008-152872 | Jun 2008 | JP | national |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/JP2009/055987 | 3/25/2009 | WO | 00 | 3/7/2011 |
