Abstract:
A system for controlling contaminant deposition in an exhaust recirculation cooler mounted in a vehicle to allow exhaust gas to recirculate along a gas recirculation path from the exhaust assembly of the engine to the intake assembly of the engine. The cooler includes a housing defining an exhaust gas inlet leading to an internal gas cooling passageway which, in turn, leads to an exhaust gas outlet. A controller receives flow dependent signals and, in turn, regulates the flow of exhaust gas through the cooler to establish a turbulent flow in order to control the production of deposits in the cooler. Multiple, varying size coolers can be employed, with separate exhaust flows to the coolers being varied in by determining which coolers should be active, while still maintaining turbulent flow patterns.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention pertains to the art of exhaust gas recirculation coolers used in association with internal combustion engines having exhaust gas recirculation systems designed to reduce pollution and, more specifically, to controlling contaminant deposition in exhaust gas recirculation coolers. 
       BACKGROUND OF THE INVENTION 
       [0002]    Conventional internal combustion engines produce various pollutants during operation. Generally, most internal combustion engines develop power by burning a hydrocarbon fuel in the presence of air, a mixture of mostly nitrogen and oxygen along with other minor components. During the burning, several exhaust constituents are produced. Some, such as water, are considered rather harmless. Others, such as nitrogen oxides (NOx) are regulated and the production of this pollutant must be controlled. In order to reduce the production of nitrogen oxides, often an exhaust gas recirculation system, hereinafter an EGR system, is provided. In an EGR system, a portion of the exhaust gas from an internal combustion engine is recirculated along a path back into an air intake of the engine. The recirculation of exhaust generally reduces the relative amount of oxygen available for combustion and thus reduces the flame temperature in the engine during combustion. A lower flame temperature greatly reduces the production of nitrogen oxides. Another way to reduce the combustion temperature is to reduce the temperature of the recirculated exhaust. Typically, a cooler is placed in the recirculation path and causes the recirculated exhaust gas to enter the engine at a reduced temperature, thus further reducing the temperature of combustion. Indeed, to reach certain legislative guidelines for emission levels, the exhaust gases must be cooled to some extent. 
         [0003]    EGR systems have been used in gasoline engines for at least 30 years and such use is ubiquitous. The use of EGR systems in Diesel engines is more recent. Diesel engines will tolerate more EGR flow than gasoline engines and thus EGR cooling in a Diesel EGR system is important. The coolers in such systems usually have a large heat transfer surface to aid in the transfer of heat from the recirculating exhaust gas to a coolant. Generally, the coolant is introduced behind the heat transfer surface to allow heat to easily pass from the recirculating exhaust gas to the coolant. Unfortunately, during operation of an EGR system, various deposits of soot and other contaminants may accumulate on the heat transfer surface in the cooler and on other conduit portions of the EGR system. The layer of soot will build up in as little as one hundred hours of operation and significantly reduce the ability of the cooler to transfer heat from the recirculating exhaust gas. More specifically, the layer of soot and other contaminants greatly reduces the efficiency of the coolers, thus leading to relatively hot recirculating exhaust gas arriving at the engine intake and reducing the engine&#39;s ability to produce power while meeting emissions standards. Such a problem is particularly acute in connection with a Diesel engine. 
         [0004]    One approach to this problem has been to employ large coolers. However, the use of large coolers has been considered undesirable because of the high cost and large size. Other approaches have been directed at reducing the amount of deposits. For example, U.S. Patent Application Publication No. 2007/0131207 to Nakamura teaches regulating coolant flow through a cooler based on sensed inlet temperature to reduce deposits. Unfortunately, such a system is based on the principle of increasing the temperature of the recirculating gas. The system is therefore undesirable because it is directly contrary to the concept of reducing the temperature of recirculating exhaust gas to reduce combustion temperature and nitrous oxide production. 
         [0005]    Based on the above there is a need in the art for a system designed to control the build up of contaminants in EGR coolers while avoiding the disadvantages set forth above. 
       SUMMARY OF THE INVENTION 
       [0006]    The present invention is directed to a system for controlling contaminant deposition in an exhaust recirculation cooler mounted in a vehicle. In general, the vehicle includes a frame supporting an engine operatively connected to a transmission and wheels so as to drive the wheels and move the vehicle. The system comprises a cooler including a housing defining a gas inlet in communication with a first conduit, as well as a gas outlet in communication with a second conduit and connected to the gas inlet by a gas cooling passageway so as to allow exhaust gas to recirculate along a gas recirculation path from the exhaust assembly of the engine to an air intake assembly of the engine. The system also comprises a coolant outlet connected to a coolant inlet by a passageway to allow coolant to flow through the cooler. The coolant passageway is positioned so as to allow heat from the exhaust gas to pass into the coolant, thus cooling the exhaust gas. A valve is located in the gas recirculation path for controlling a flow rate of the exhaust gas in the cooler and a sensor is mounted for measuring a parameter of the exhaust gas in the gas recirculation path. A controller receives the parameter signals from the sensor and is connected to the valve. More specifically, the controller regulates the opening and closing of the valve in a manner which ensures that the exhaust gas in the cooler flows in a turbulent state in order to remove deposits from the cooler. 
         [0007]    Optionally, an additional cooler, including a housing defining a gas inlet in communication with the first conduit and a gas outlet, is placed in communication with the second conduit and connected to the gas inlet by a gas cooling passageway. Additionally, a coolant outlet is connected to an inlet by a passageway to allow coolant to flow through the additional cooler. The coolant passageway is positioned so as to allow heat from the exhaust gas to pass into the coolant, thus cooling the exhaust gas. A master valve may be provided for controlling an overall flow rate through the recirculation path and an additional valve is provided for controlling a flow rate of gas through the additional cooler. The valves are located between the air intake assembly and the coolers or between the air exhaust assembly and the coolers. 
         [0008]    The present invention is also directed to a method of controlling contaminant deposition in exhaust gas recirculation coolers. A flow of recirculating exhaust gas is directed from the exhaust assembly of the engine back to the air inlet assembly of the engine so as to reduce the amount of pollutants in the exhaust gas. The control module establishes a flow rate of an exhaust gas in the cooler and receives measurements of various parameters of the exhaust gas. Finally, the control module ensures that the flow rate of the exhaust gas in the cooler is turbulent so as to remove deposits from the cooler. Preferably, multiple coolers are used and the control module directs the flow of exhaust gas through the multiple coolers. Optionally, the module determines the Reynolds number associated with the flow of gas through the cooler and ensures that the Reynolds number stays within a range associated with turbulent flow. 
         [0009]    Additional objects, features and advantages of the present invention will become more readily apparent from the following detailed description of preferred embodiments when taken in conjunction with the drawings, wherein like reference numerals refer to corresponding parts in the several views. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0010]      FIG. 1  is a schematic view of a vehicle incorporating a system for controlling contaminant deposition in exhaust gas recirculation coolers embodying the invention; 
           [0011]      FIG. 2  is a schematic view of the system of  FIG. 1  shown in a simplified form with hot side control valves; 
           [0012]      FIG. 3  is a schematic view of the system of  FIG. 1  shown in a simplified form with cold side control valves; 
           [0013]      FIG. 4  is a schematic view of one of the coolers in  FIG. 1 ; 
           [0014]      FIG. 5  is a cross-sectional view of the cooler in  FIG. 4  taken along the line V-V; and 
           [0015]      FIG. 6  is flowchart showing a method of operating the system of  FIG. 1 . 
       
    
    
     DESCRIPTION OF PREFERRED EMBODIMENTS 
       [0016]    With initial reference to  FIG. 1 , there is shown a schematic view of a vehicle  10  incorporating a system  20  for controlling contaminant deposition in an exhaust gas recirculation cooler, as constructed in accordance with a preferred embodiment of the invention. As illustrated, an engine  25  including multiple cylinders  26  is mounted in vehicle  10 . Preferably, engine  25  is a Diesel engine and vehicle  10  is a truck. However, vehicle  10  may be any type of vehicle and the system will work with other combustion engines that utilize pollution control devices including exhaust gas recirculation coolers. As shown, radiator  30  is provided to cool engine  25 . In addition, vehicle  10  includes a frame  32  which supports various components such as engine  25  used to drive wheels  36  through a powertrain  38  including a transmission and drive shaft (not separately labeled). 
         [0017]    As seen in  FIG. 2 , engine  25  has both an air intake assembly  39  and an exhaust assembly  40 . Engine  25  is connected to a source of fuel  41  and a booster  42 , such as a turbo charger  44 , for increasing a flow of intake air indicated by arrow  45  to engine  25 . More specifically air enters system  20  through an airbox  47  and travels through a passage  50  to turbocharger  44 . An air mass air flow unit  52  is mounted in passage  50  and includes a sensor  55  for measuring the amount of air passing to turbocharger  44 . Sensor  55  is connected to an electronic control module  57 . Sensor  55  is able to provide to electronic control module  57  a signal, shown as arrow  60 , which is representative of the amount of air passing to turbocharger  44 . Additionally, mass airflow unit  52  includes a valve  62  that receives signals from electronic control module  57  and functions to control the amount of air passing therethrough. 
         [0018]    In a manner widely known in the art, turbocharger  44  compresses air received from airbox  47  and provides a charge of air which passes through a charge cooler  65 . Charge cooler  65  cools the charge and sends the charge to a manifold  67  for distribution to cylinders  26 . Engine  25  receives both the charge and fuel which are combusted, thus producing power used to drive vehicle  10  and combustion products which are exhausted from vehicle  10  at exhaust  68 . 
         [0019]    With continuing reference to  FIG. 2 , system  20  is shown sending a diverted exhaust flow, i.e., a recirculated exhaust gas (EGR) flow, represented by arrow  70 , of exhaust  68  produced by engine  25  through a first conduit  71  to a cooling system  72  and then supplies a cooled portion  75  of diverted exhaust flow  71  through a second conduit  77  to inlet manifold  67 , thus completing a gas recirculation path  69  from air exhaust assembly  40  to air intake assembly  39 . More specifically, system  20  includes first conduit  71  connected to exhaust assembly  40 . First, conduit  71  is preferably equipped with an exhaust backpressure sensor  82  and an exhaust temperature sensor  85  which measure the exhaust backpressure and temperature, respectively. Sensors  82  and  85  are connected to electronic control module  57  by wires  87  and  88 , or other known types of communication channels, and thus are able to provide electronic control module  57  with signals representative of the exhaust backpressure and temperature. Optionally, a master control valve  90  is located in first conduit  71  and arranged to restrict the amount of diverted exhaust flow  70  passing therethrough. Master valve  90  is also connected to electronic control module  57  by a wire  91  or other type of communication channel so that control module  57  can control the amount of exhaust that is in diverted exhaust flow  70 . First conduit  71  ends at a junction  92  which splits diverted exhaust flow  70  into two or more paths, each path leading to a respective exhaust gas cooler  22 ,  97  or  98 . 
         [0020]    As shown there are three coolers  22 ,  97  and  98 , with first cooler  22  connected to a first path  100 , second or additional cooler  97  connected to a second path  101  and third cooler  98  connected to a third path  102 . However, it is to be understood that the invention will work with varying number of coolers. First or main cooler  22  cools a first portion of diverted exhaust flow  70 . A first EGR valve  105  is positioned between first path  100  and first cooler  22 . First EGR valve  105  is also in communication with electronic control module  57  through a communication path  110  so that electronic control module  57  can control the amount of diverted exhaust that passes therethrough. A first coolant feed  112  supplies coolant, as represented by arrow  113 , to first cooler  22  from radiator  30  and a return feed  115  directs coolant  113  back to radiator  30  such that the coolant travels in a recirculating path. Coolant  113  is used by first cooler  22  to cool diverted exhaust  70 . 
         [0021]    In a similar manner, a second EGR valve  120  is positioned between second path  101  and second cooler  97 ; and a third EGR valve  125  is positioned between third path  102  and third cooler  98 . Each of second and third EGR valves  120 ,  125  is also connected to electronic control module  57 . In this manner, control module  57  can individually control a flow rate of an amount of diverted exhaust gas  70  passing through each of coolers  22 ,  97  and  98 . Indeed, if no master valve  90  is present, control module  57  may use valves  105 ,  120 ,  125  to control the overall amount of diverted flow  70  passing through coolers  22 ,  47 ,  98 . Likewise, each of the second and third coolers  97 ,  98  has a respective second and third coolant feed  130 ,  131  and a respective second and third coolant return  133 ,  134  attached to radiator  30  for providing recirculating coolant paths so that second and third coolers  97 ,  98  can use coolant  113  to cool the second and third diverted amounts of exhaust passing therethrough. At this point, it should be understood that electronic control module  57  need not be dedicated for use with the exhaust system, but preferably constitutes a main electronic control unit for vehicle  10  so as to control various engine, transmission and other functions. Also, although a preferred arrangement of sensors has been disclosed, different sensors can be used in combination with electronic control module  57  to indirectly derive the desired measurements. Three coolers are shown by way of example and this embodiment is not intended to be limiting. In alternate embodiments, two coolers are used. 
         [0022]    In the embodiment shown in  FIG. 2 , EGR valves  90 ,  105 ,  120  and  125  are shown upstream of EGR coolers  22 ,  97  and  98 . Generally, the diverted exhaust gas passing through EGR valves  90 ,  105 ,  120  and  125  will be relatively hot. This arrangement has the advantage of relatively low build up of sludge around EGR valves  90 ,  105 ,  120  and  125 . However, EGR valves  90 ,  105 ,  120  and  125  have to be designed to operate in a relatively hot environment. In an alternative embodiment shown in  FIG. 3 , corresponding EGR valves  90 ′,  105 ′,  120 ′ and  125 ′ are located downstream of EGR coolers  22 ,  97  and  98 . In this case first, second and third EGR valves  105 ′,  120 ′, and  125 ′ are located between the respective first, second and third coolers  22 ,  97  and  98  and respective first, second and third return paths  140 ,  141 ,  142  which lead to second conduit  77 . This alternative embodiment has the advantage of allowing a master valve  90 ′ and the first, second and third EGR valves  105 ′,  120 ′ and  125 ′ to operate in relatively cool conditions. However, the tradeoff is that there is an increased amount of sludge build up. In all other respects, the two embodiments are the same such that a further discussion thereof is not necessary. 
         [0023]    Turning now to  FIG. 4 , there is shown a more detailed view of first cooler  22 . It should be understood that coolers  22 ,  97  and  98  are preferably constructed to be substantially identical, although the size of each cooler is preferably set based on the needs of engine  25 , as more fully discussed below. With this in mind, cooler  22  is shown to include a housing  143  defining a gas inlet  144  in communication with first conduit  71  and a gas outlet  145  in communication with second conduit  72 . Housing  143  also defines a gas cooling passageway  146  that connects gas inlet  144  to gas outlet  145 . Coolant from first coolant feed  112  enters first cooler  22  at coolant inlet  147  and travels through passages  150  in first cooler  22  to a coolant outlet  148  connected to coolant return feed  115 . Passages  150  extend longitudinally and establish a heat transfer surface  153  made from a material that resists damage by corrosive exhaust gases and readily transfers heat from diverted exhaust  70  to a coolant flow indicated at  155 . As best seen in  FIG. 5 , fins  160  preferably extend from passages  150  to further increase heat transfer by enlarging heat transfer surface  153 . In another embodiment, the material forming fins  160  and passages  150  establish a texture that increases the turbulence of the flow of diverted exhaust passing around fins  160 . 
         [0024]      FIG. 6  shows a flowchart indicating the operation of system  20  for controlling contaminant deposition in EGR coolers according to a preferred embodiment of the invention. As shown in step  200 , during operation of engine  25 , portion  70  of the exhaust flow is diverted from exhaust assembly  40  through first cooler  22  and then recirculated back to air intake assembly  39  along recirculation path  69 . As noted above, during engine operation, soot and other deposits may accumulate on the inside surfaces of cooler  22 . Cooler fins  160  are particularly prone to collecting soot. If a layer of soot covers fins  160 , they will not function properly. To counter this potential problem, as engine  25  starts, a certain flow rate is established through first cooler  22  as shown in step  210 . Various parameters, as discussed further below, are then measured in step  220  to calculate if the flow through cooler  22  is laminar or turbulent. Electronic control module  57  then adjusts valves  90 ,  105  to ensure in step  240  that the exhaust flow through first cooler  22  stays in the turbulent range. A more detailed example of how electric control module  57  ensures the exhaust flow is turbulent is found below in the description of  FIG. 7 . The advantage of keeping the flow in the turbulent range is that such flow unexpectedly functions to effectively shake off deposits that may have formed on the inside surface of cooler  22  or on fins  160 . Once the soot or other deposits are shaken off of cooler  22 , the soot travels back through the engine cylinders  26  and is eventually exhausted. Without the layer of soot build up, first cooler  22  operates with a much greater efficiency, thereby allowing the use of a smaller, lighter and cheaper unit than available in the past. 
         [0025]    One of the parameters that is controlled is the Reynolds number. The Reynolds number is based on, among other things, the speed, temperature, gas flow and hydraulic diameter of a passage. As shown in  FIGS. 2 and 3 , the exhaust backpressure and temperature are measured by sensors  82 ,  85 . Electronic control module  57  calculates the Reynolds number based on the measured parameters and ensures that the flow stays in the turbulent mode by maintaining the Reynolds number in an appropriate range. However, it should be noted that other sensors may be used to obtain the parameters needed to calculate the Reynolds number. Such parameters may also be inferred based on the air flow, fuel injection parameters and other known or measured engine parameters because the performance characteristics of engine  26  may be known. For example, the exhaust backpressure could be inferred based on a measured air inflow and the characteristics of engine  26 , instead of measuring the exhaust backpressure directly. The determination of whether a flow through cooler  22  is turbulent or laminar is preferably done by testing to determine what flow rates cause turbulent flow and to produce a look up table for control module  57 . Once control module  57  determines what EGR flow is required by engine  25 , valve  105  to cooler  22  is adjusted to obtain turbulent flow as much as possible. 
         [0026]    The use of multiple coolers  22 ,  97  and  98  may be required or desirable. In such a case, each cooler  22 ,  97  and  98  is controlled to run with an optimal Reynolds number so the respective flow is turbulent. For example, the first and second coolers  22 ,  97  are preferably different sizes, with first cooler  22  being a small cooler and the second cooler  97  being a larger cooler. When engine  26  is running at low speed, small cooler  22  is used. When engine  25  is running at medium speed, large cooler  97  is used and when engine  25  is running at a high speed, both coolers  22 ,  97  are used. With differently sized coolers  22 ,  97 , a larger range of flow rates can be kept in the turbulent regime as flow  70  passes through the cooler  27 ,  97 . Depending on the particular operating characteristics of the engine, three or more coolers  22 ,  97  and  98  may be employed. In any is event, when multiple coolers  22 ,  97  and  98  are used, electronic control unit  57  regulates the flow through the coolers as needed in order to maintain each related Reynolds number in the proper range by opening and closing the appropriate EGR valves  105 ,  105 ′,  120 ,  120 ′,  125  and  125 ′. Again, since controller  57  has more options for flow rates through coolers  22 ,  97 ,  98  when multiple coolers are used, the flow through coolers  22 ,  97 ,  98  can be kept turbulent over a larger range. Control module  57  determines how many coolers should be used for a given EGR flow rate  70  demanded by engine  25 . 
         [0027]    Turning now to  FIG. 7 , there is shown a flow chart depicted an exemplary control logic that may be used by control module  57  for controlling two coolers  22 ,  97 . At step  300 , a process starts and initially determines at step  310  whether or not exhaust gas recirculation flow is needed. If EGR flow is needed, control module  57  proceeds to step  320  and determines a desired EGR flow rate which is needed to control the emissions of NOx. Since engine  25  requires different EGR flow rates depending on running conditions, such as vehicle speed, the required flow rate may change. Once the required flow rate is determined, control module  57  at step  330  determines whether the EGR mass flow rate is in either a first, second or third range. If the gas flow is in a relatively low first range, then control module  57  sends a signal to open valve  105  to provide the desired EGR flow for engine  25  and, in addition, to ensure that turbulent flow is present in cooler  22 . However, if the mass flow rate is in a second, higher range, then control module  57  opens valve  120  and closes  105  to have EGR flow travel through larger cooler  97  thus providing the desired EGR flow and still ensuring a turbulent flow through cooler  97 . If the mass flow rate is in a higher third range, then both valves  105  and  120  are open in step  360  to provide the desired EGR flow cooling and to ensure that turbulent flow exists in both coolers  22  and  97 . In any one of the three paths at step  370 , the process will return to step  300  if there are changes in the required EGR flow rates. The above discussion of course assumes only two coolers, coolers  22  and  97 , are being used. If a third cooler  98  is used, of course the search logic becomes a little bit more complicated in that three valves should be used and a possible six different flow ranges may be provided. 
         [0028]    Based on the above, it should be readily apparent that the present invention provides for a system that controls the build up of contaminants in EGR coolers while avoiding the disadvantages as set forth in the prior art. Although described with reference to preferred embodiments of the invention, it should be readily understood that various changes and/or modifications could be made to the invention without departing from the spirit thereof. For instance, numerous additional EGR coolers may be added to the system as needed and the system may be adapted to any engine, with or without a charge booster, that incorporates an EGR system. In general, the invention is only intended to be limited by the scope of the following claims.