Abstract:
An exhaust system for an internal combustion engine comprises a turbocharger, an exhaust pipe, a first diesel particulate filter, a second diesel particulate filter, and a flow control valve. The exhaust pipe has a first portion, a second portion, and a third portion. At least the second portion of the exhaust pipe comprises a plurality of fluid paths. The first diesel particulate filter is coupled to on one of the plurality of fluid paths between the second portion and the third portion of the exhaust pipe. The second diesel particulate filter is coupled to another of the plurality of fluid paths. The flow control valve is disposed within the second portion of the exhaust pipe. The flow control valve is response to an input signal indicative of an operating condition and is configured to control exhaust flow to the first diesel particulate filter and the second diesel particulate filter in response to the input signal.

Description:
TECHNICAL FIELD 
       [0001]    The present disclosure relates to an engine having an exhaust system with a plurality of diesel particulate filters, and more particularly to an exhaust system with improved regeneration of the diesel particulate filters while the engine is experiencing either heavy load conditions or idle load conditions. 
       BACKGROUND 
       [0002]    Many modern diesel engines have an exhaust system that features at least one diesel particulate filter. The diesel particulate filter is utilized to collect particulate matter, often referred to as “soot,” that is generated during the combustion of fuel by the engine. After a period of engine operation, the diesel particulate filter needs to be regenerated in order to continue to function as intended. During regeneration, the temperature of the diesel particulate filter is raised such that particulate matter within the filter is combusted. During heavy engine load conditions, the temperature of exhaust gas is already high, thus further increasing the temperature of the exhaust gas during regeneration may cause damage. Alternatively, during idle loading conditions, the temperature of the exhaust gas may not be high enough to ignite fuel that may be injected into the diesel particulate filter that is used to combust the particulate matter within the filter. Therefore, a need exists for an exhaust system that allows regeneration of a diesel particulate filter at high engine load conditions that does not raise exhaust gas temperatures above a certain temperature, but that also produces exhaust gas temperatures that allows regeneration of a diesel particulate filter at idle loading conditions. 
       SUMMARY 
       [0003]    According to one embodiment, an exhaust system for an internal combustion engine comprises a turbocharger, an exhaust pipe, a first diesel particulate filter, a second diesel particulate filter, and a flow control valve. The exhaust pipe has a first portion, a second portion, and a third portion. At least the second portion of the exhaust pipe comprises a plurality of fluid paths. The first diesel particulate filter is coupled to on one of the plurality of fluid paths between the second portion and the third portion of the exhaust pipe. The second diesel particulate filter is coupled to another of the plurality of fluid paths. The flow control valve is disposed within the second portion of the exhaust pipe. The flow control valve is response to an input signal indicative of an operating condition and is configured to control exhaust flow to the first diesel particulate filter and the second diesel particulate filter in response to the input signal. 
         [0004]    According to one process, a method of regenerating a diesel particulate filter while an engine is operating under a normal load is provided. An exhaust pipe is provided in fluid communication with exhaust from an engine. The exhaust pipe has a first portion, a second portion, and a third portion. At least the second portion of the exhaust pipe comprises a plurality of fluid paths. A first diesel particulate filter and a second diesel particulate filter are provided. The first diesel particulate filter is coupled to one of the plurality of flow paths. The second diesel particulate filter is coupled to another of the plurality of fluid flow paths. The first and second diesel particulate filters form generally parallel flow paths for exhaust gas. Exhaust flow is directed using a flow control valve disposed in the second portion of the exhaust pipe to the first diesel particulate filter and the second diesel particulate filter. Fuel is delivered to one of either the first diesel particulate filters and the second diesel particulate filter with a fuel dosing input. Exhaust gas mixes downstream of the first diesel particulate filter and the second diesel particulate filter with an exhaust mixer. 
         [0005]    According to another process, a method of regenerating a diesel particulate filter while an engine is operating under an idle load is provided. An exhaust pipe is provided in fluid communication with exhaust from an engine. The exhaust pipe has a first portion, a second portion, and a third portion. At least the second portion of the exhaust pipe comprise a plurality of fluid paths. A first diesel particulate filter and a second diesel particulate filter are provided. The first diesel particulate filter is coupled to one of the plurality of flow paths. The second diesel particulate filter is coupled to another of the plurality of fluid flow paths. The first and second diesel particulate filters form generally parallel flow paths for exhaust gas. Exhaust flow is directed using a flow control valve disposed in the second portion of the exhaust pipe to one of the first diesel particulate filter and the second diesel particulate filter. Fuel is delivered with a fuel dosing input to the one of the first diesel particulate filters and the second diesel particulate filter that exhaust flow is directed. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0006]      FIG. 1  is a schematic diagram showing an engine having an exhaust system with a plurality of diesel particulate filters. 
       
    
    
     DETAILED DESCRIPTION 
       [0007]      FIG. 1  shows an engine  10  having an exhaust system  12 . The engine  10  is disposed in fluid communication with a fuel reservoir  14  via fuel supply line  16   a  and fuel return line  16   b.    
         [0008]    The exhaust system  12  has a plurality of diesel particulate filters (“DPFs”) including a first DPF  18   a  and a second DPF  18   b . The exhaust system  12  includes an exhaust manifold  20 , and a turbocharger  22  disposed in fluid communication with the exhaust manifold  20 . The turbocharger  22  may be directly connected to the exhaust manifold  20 . Exhaust flows from the turbocharger  22  via a first portion  24   a  of an exhaust pipe  24 . The first portion  24   a  of the exhaust pipe  24  runs from an outlet of the turbocharger  22  to a flow control valve  26 . 
         [0009]    The flow control valve  26  is adapted to control the flow of exhaust to a second portion  24   b  of the exhaust pipe  24 . The second portion  24   b  of the exhaust pipe  24  forms a plurality of fluid flow paths. As shown in  FIG. 1 , the second portion  24   b  of the exhaust pipe is generally Y-shaped and forms a first passage leading to the first DPF  18   a  and a second passage leading to the second DPF  18   b . The flow control valve  26  may be positioned to generally three positions to allow exhaust gas to flow in generally three ways: to both the first DPF  18   a  and the second DPF  18   b ; to the first DPF  18   a ; or the second DPF  18   b.    
         [0010]    The exhaust system  12  includes a turbocharger bypass  28  that connects the exhaust manifold  20  to the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass  28  includes a bypass valve  30  that is adapted to allow exhaust gas to flow to either the first DPF  18   a , or the second DPF  18   b  without passing through the turbocharger  22 . The bypass valve  30  may also be closed to prevent exhaust that has not passed through the turbocharger  22  from entering the first DPF  18   a  and the second DPF  18   b . Exhaust that passes through the turbocharger bypass  28  generally has a higher temperature than exhaust that passes through the turbocharger  22 . 
         [0011]    The second portion  24   b  of the exhaust pipe  24  additionally has a first fuel dosing input  32   a  and a second fuel dosing input  32   b . The fuel dosing inputs  32   a ,  32   b  are adapted to supply fuel from the fuel reservoir  14  to the exhaust system  12  during regeneration of the first DPF  18   a , and the second DPF  18   b  to assist in combusting the particulate matter during the regeneration. 
         [0012]    Downstream of the first DPF  18   a  and the second DPF  18   b  of the exhaust system  12  is a third portion  24   c  of the exhaust pipe  24 . The third portion  24   c  of the exhaust pipe  24  recombines the exhaust flow from the first DPF  18   a  and the second DPF  18   b . The third portion  24   c  of the exhaust pipe  24  is also generally Y-shaped. The third portion  24   c  of the exhaust pipe  24  runs to an exhaust mixer  34 . The exhaust mixer  34  is adapted to cause turbulent flow such that exhaust that has passed through the first DPF  18   a  mixes thoroughly with exhaust gas that has passed through the second DPF  18   b . Therefore, exhaust leaving the exhaust mixer  34  will generally be of the average temperature of exhaust passing through the first DPF  18   a , and the second DPF  18   b  when exhaust is flowing through both DPFs  18   a ,  18   b.    
         [0013]    While the engine  10  is operating normally, exhaust gas flows from the exhaust manifold  20  through the turbocharger  22  and into the first portion  24   a  of the exhaust pipe  24 . The flow control valve  26  is positioned to allow exhaust gas to flow to both the first DPF  18   a  and the second DPF  18   b  from the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass valve  30  is closed during normal engine operation, such that no exhaust flows through the turbocharger bypass  28 . Additionally, no fuel is provided to the fuel dosing inputs  32   a ,  32   b  during normal engine operations. 
         [0014]    During regeneration of the first DPF  18   a  when the engine is operating under normal or higher loads, exhaust gas flows from the turbocharger  22  and into the first portion  24   a  of the exhaust pipe  24 . The flow control valve  26  is positioned to allow exhaust gas to flow to both the first DPF  18   a  and the second DPF  18   b  from the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass valve  30  is positioned to allow exhaust to flow to the first DPF  18   a  via the turbocharger bypass  28 . Fuel is provided to the first DPF  18   a  from the fuel reservoir  14  from the first fuel dosing input  32   a . The fuel that enters the first DPF  18   a  from the first fuel dosing input  32   a  ignites and raises the temperature within the first DPF  18   a  such that particulate matter within the first DPF  18   a  combusts. The exhaust from the first DPF  18   a  mixes with the exhaust from the second DPF  18   b  within the exhaust mixer  34 , such that at the temperature of exhaust at an output of the exhaust mixer is generally the average temperature of the exhaust from the first DPF  18   a  and the second DPF  18   b . Therefore, the temperature of the exhaust leaving the mixer  34  is significantly lower than the exhaust leaving the first DPF  18   a.    
         [0015]    During regeneration of the second DPF  18   b  when the engine is operating under normal or higher loads, exhaust gas flows from the turbocharger  22  and into the first portion  24   a  of the exhaust pipe  24 . The flow control valve  26  is positioned to allow exhaust gas to flow to both the first DPF  18   a  and the second DPF  18   b  from the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass valve  30  is positioned to allow exhaust to flow to the second DPF  18   b  via the turbocharger bypass  28 . Fuel is provided to the second DPF  18   b  from the fuel reservoir  14  from the second fuel dosing input  32   b . The fuel that enters the second DPF  18   b  from the second fuel dosing input  32   b  ignites and raises the temperature within the second DPF  18   b  such that particulate matter within the second DPF  18   b  combusts. The exhaust from the first DPF  18   a  mixes with the exhaust from the second DPF  18   b  within the exhaust mixer  34 , such that at the temperature of exhaust at an output of the exhaust mixer is generally the average temperature of the exhaust from the first DPF  18   a  and the second DPF  18   b . Therefore, the temperature of the exhaust leaving the mixer  34  is significantly lower than the exhaust leaving the second DPF  18   b.    
         [0016]    During regeneration of the first DPF  18   a  when the engine is operating under idle or light loads, exhaust gas flows from the turbocharger  22  and into the first portion  24   a  of the exhaust pipe  24 . The flow control valve  26  is positioned to allow exhaust gas to flow to only the first DPF  18   a  from the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass valve  30  is positioned to allow exhaust to flow to the first DPF  18   a  via the turbocharger bypass  28 . As exhaust is only flowing through the first DPF  18   a , additional back pressure formed within the exhaust pipe  24  raises the temperature of the exhaust, and causes additional flow through the turbocharger bypass  28 , additionally raising the temperature of the exhaust gas within the first DPF  18   a . Fuel is provided to the first DPF  18   a  from the fuel reservoir  14  from the first fuel dosing input  32   a . The fuel that enters the first DPF  18   a  from the first fuel dosing input  32   a  ignites and raises the temperature within the first DPF  18   a  such that particulate matter within the first DPF  18   a  combusts. The use of the flow control valve  26  and the turbocharger bypass  28  raises the temperature of the exhaust within the first DPF  18   a  to a sufficiently high temperature to ignite the fuel from the first fuel dosing input  32   a  even during idle loading. 
         [0017]    Similarly, during regeneration of the second DPF  18   b  when the engine is operating under idle or light loads, exhaust gas flows from the turbocharger  22  and into the first portion  24   a  of the exhaust pipe  24 . The flow control valve  26  is positioned to allow exhaust gas to flow to only the second DPF  18   b  from the second portion  24   b  of the exhaust pipe  24 . The turbocharger bypass valve  30  is positioned to allow exhaust to flow to the second DPF  18   b  via the turbocharger bypass  28 . As exhaust is only flowing through the second DPF  18   b , additional back pressure formed within the exhaust pipe  24  raises the temperature of the exhaust, and causes additional flow through the turbocharger bypass  28 , additionally raising the temperature of the exhaust gas within the second DPF  18   b . Fuel is provided to the second DPF  18   b  from the fuel reservoir  14  from the second fuel dosing input  32   b . The fuel that enters the second DPF  18   b  from the second fuel dosing input  32   b  ignites and raises the temperature within the second DPF  18   b  such that particulate matter within the second DPF  18   b  combusts. The use of the flow control valve  26  and the turbocharger bypass  28  raises the temperature of the exhaust within the second DPF  18   b  to a sufficiently high temperature to ignite the fuel from the second fuel dosing input  32   b  even during idle loading. 
         [0018]    The first and second DPFs  18   a ,  18   b  are generally each about 70% the size of a single DPF that would be required for the exhaust system  12 . 
         [0019]    While two DPFs are shown in  FIG. 1 , it is contemplated that the number of DPFs used may increase. The greater the number of DPFs utilized in an exhaust system, the smaller each individual DPF may be. For example, if three DPFs are utilized, each DPF is about 60% the size of single DPF that would otherwise be needed, and if four DPFs are utilized, each DPF is about 50% of the size of a single DPF. If more than two DPFs are utilized, additional flow control valves and portions of the exhaust pipe will be required to control the flow of exhaust to specific DPFs. The use of more than two DPFs helps to keep exhaust temperatures from rising to a temperature that may cause damage during high load DPF regeneration, while also ensuring that exhaust temperatures will remain high enough for DPF regeneration to occur under idle loads.