Abstract:
A system and method for controlling EGR of an internal combustion engine is presented. The system is capable of controlling EGR over a wide range of flow rates.

Description:
FIELD  
       [0001]    The present description relates to a system and method for exhaust gas recirculation (EGR) that exhibits control over a large range of flow rates. 
       BACKGROUND  
       [0002]    Exhaust gas recirculation (EGR) between an exhaust manifold and intake manifold may be regulated in many ways. One device for controlling EGR is presented in European Patent Application 0137282. This method describes controlling a series of valves in an attempt to achieve a desired EGR flow rate. In particular, valves are set to an open position in combinations that approach the desired EGR flow rate. In one example, the valves are selected from a binary pattern that represents a predetermined EGR flow rate. The selected binary pattern changes with engine speed and temperature. 
         [0003]    The above-mentioned method can also have several disadvantages. Namely, the valves operate in a completely open-loop manner. That is, the engine controller selects a number and pattern of valves that are suppose to deliver the desired EGR flow rate. However, over time carbon deposits may alter the flow characteristics of the valves such that a different amount of EGR flows than is desired. In addition, since the valves are controlled in a binary fashion, the EGR flow rate will be interrupted and discontinuous when the number of open valves changes. 
         [0004]    The inventors herein have recognized the above-mentioned disadvantages and have developed a system and method to deliver EGR to an internal combustion engine that offers substantial improvements. 
       SUMMARY  
       [0005]    One example approach to overcome at least some of the disadvantages of prior approach includes a system for controlling exhaust gas recirculation of an internal combustion engine, system comprising: a first valve positioned to control flow through a first conduit; a second valve positioned to control flow through a second conduit; and a controller to position said first valve in response to a pressure in said first conduit and a pressure in said second conduit when said second valve is closed, and to position said second valve in response to a pressure in said second conduit and a pressure in said first conduit when said first valve is closed. This method can be used to reduce the above-mentioned limitations of the prior art approach. 
         [0006]    A two orifice EGR valve can be controlled to deliver a wide dynamic range of EGR flow rates. In one example, a single differential pressure transducer can be used to determine EGR flow through two separate orifices. The EGR flow rate can be used by a controller to position valves that control the flow rate through the respective orifices. This arrangement allows EGR flow to be continuously controlled over a wide flow rate range. In addition, since the orifices can be sharp edged orifices they tend to be less affected by carbon in exhaust gases. Consequently, the orifice and controller allow more precise control of EGR over a long period of time and a variety of engine operating conditions. 
         [0007]    The present description provides several advantages. Specifically, the method can provide continuous and uninterrupted EGR flow over a wide range of engine operating conditions. The system and method also provide unexpected results. Specifically, system cost can be reduced and system reliability can be increased when the present system and method is compared to other high flow rate EGR systems. By ingeniously configuring the system to utilize a single sensor to provide EGR flow feedback, system cost is reduced because a sensor is not necessary for each orifice. Furthermore, reliability is increased because a single sensor is used to determine EGR flow rates through two different orifices. By reducing the number of sensors, there is a lower possibility of sensor degradation in the system, and this increases system reliability. 
         [0008]    The above advantages and other advantages, and features of the present description will be readily apparent from the following Detailed Description when taken alone or in connection with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0009]    The advantages described herein will be more fully understood by reading an example of an embodiment, referred to herein as the Detailed Description, when taken alone or with reference to the drawings, wherein: 
           [0010]      FIG. 1  is a schematic diagram of an engine; 
           [0011]      FIG. 2  is a schematic diagram of an EGR control apparatus; and 
           [0012]      FIG. 3  is a flow chart of an example engine EGR strategy. 
       
    
    
     DETAILED DESCRIPTION  
       [0013]    Referring to  FIG. 1 , internal combustion engine  10 , comprising a plurality of cylinders, one cylinder of which is shown in  FIG. 1 , is controlled by electronic engine controller  12 . Engine  10  includes combustion chamber  30  and cylinder walls  32  with cam shaft  130  and piston  36  positioned therein and connected to crankshaft  40 . Combustion chamber  30  is known communicating with intake manifold  44  and exhaust manifold  48  via respective intake valve  52  an exhaust valve  54 . Exhaust manifold  48  is shown in communication with intake manifold  44  via EGR tube  46  and EGR valve  45 . Alternatively, EGR may flow from the exhaust manifold or exhaust ports to the intake ports. Fuel injector  66  is shown having a nozzle capable if injecting fuel directly into combustion chamber  30  in an amount in proportion to the pulse width of a signal from controller  12 . Fuel is delivered to fuel injector  66  by fuel system (not shown) including a fuel tank, fuel pump, and fuel rail (not shown). Intake manifold  44  is also shown communicating with throttle body  58  via throttle plate  62 . 
         [0014]    Conventional distributorless ignition system  88  provides ignition spark to combustion chamber  30  via spark plug  92  in response to controller  12 . Alternatively, the spark plug and ignition system may be removed for compression ignition engines. Two-state exhaust gas oxygen sensor  76  is shown coupled to exhaust manifold  48  upstream of catalytic converter  70 . Alternatively, a Universal Exhaust Gas Oxygen (UEGO) sensor may be substituted for two-state sensor  76 . Two-state exhaust gas oxygen sensor  98  is shown coupled to exhaust pipe  49  downstream of catalytic converter  70 . Sensor  76  provides signal EGO 1  to controller  12 . 
         [0015]    Controller  12  is shown in  FIG. 1  as a conventional microcomputer including: microprocessor unit  102 , input/output ports  104 , and read-only memory  106 , random-access memory  108 , and a conventional data bus. Controller  12  is shown receiving various signals from sensors coupled to engine  10 , in addition to those signals previously discussed, including: engine coolant temperature (ECT) from temperature sensor  112  coupled to cooling sleeve  114 ; throttle position from throttle position sensor  69 ; a measurement of manifold absolute pressure (MAP) form pressure sensor  122  coupled to intake manifold  44 ; a measurement (ACT) of engine air amount temperature or manifold temperature from temperature sensor  117 ; a cam position signal (CAM) from a variable reluctance cam sensor  150 ; and a crankshaft position signal (CPS) from a variable reluctance sensor  118  coupled to a crankshaft  40 , and an engine torque demand sensor  119 . Alternatively, other types of sensors may be substituted for the above-mentioned sensor type (e.g., Hall sensors or optical sensors may be used in place of variable reluctance sensors). 
         [0016]    Referring now to  FIG. 2 , a schematic of an example EGR control apparatus is shown. In this example valve, EGR enters the control apparatus at port  210  from the engine exhaust manifold and flows in the direction indicated by the arrow. The positions of valves  203  and  223  determine which orifice  221  or  201  exhaust gases pass through on the way to the engine intake manifold. In alternative embodiments, orifices  221  and  201  may be nozzles or venturi style orifices. Linear solenoids  225  and  205  are supplied a duty cycled voltage such that they control the position of valves  223  and  203  respectively. Alternatively, linear solenoids  205  and  225  can be replaced by linear motors or by motors having ball screws or similar translation devices. Exit ports  212  and  214  provide separate conduits from orifices  221  and  201  to the engine intake manifold. Valves  223  and  203 , orifices  221  and  201 , and conduits  216  and  218  are sized differently to provide precise control at different flow rates. Differential pressure sensor  265  senses pressure in conduits  216  and  218  via sample ports  220  and  222 . Each of these ports is positioned between an orifice and a control valve. The differential pressure sensor output may be unsigned (i.e., absolute value), if desired. 
         [0017]    The figure shows valve  203  in the closed position. While valve  203  is in the closed position pressure in conduit  218  equilibrates to the pressure in the engine intake manifold because port  214  provides a path to the intake manifold. This exposes differential pressure transducer  265  to a pressure differential that exists when there is flow through orifice  221 . Given the orifice diameter and the pressure across an orifice, Bernoulli&#39;s law can be applied to determine the EGR flow rate. The determined EGR flow rate allows a controller (e.g., controller  12 ,  FIG. 1 ) to provide closed-loop control of valve  223 . That is, a controller can monitor the flow through orifice  221  by monitoring the pressure differential across and orifice and command solenoid  225 , thereby adjusting the position of valve  223  in response to the actual flow through an orifice. If the desired EGR flow rate exceeds the flow capacity of orifice  221 , valve  223  can be closed and valve  203  opened so that the EGR flow capacity is increased. When valve  223  is closed, pressure in differential pressure sensor port  220  equilibrates to intake manifold pressure and differential pressure sensor  265  is exposed to the pressure difference across orifice  201 . Similar to flow through orifice  221 , flow through orifice  201  can be determined when the orifice diameter and pressure differential across the orifice have been determined. 
         [0018]    Note that the dimensions and layout of the EGR apparatus illustrated in  FIG. 2  can be modified without departing from the scope or intent of the present description. Accordingly, other embodiments utilizing a single differential pressure sensor to determine EGR flow through separate orifices is anticipated by the present inventors. 
         [0019]    Referring now to  FIG. 3 , a flow chart of an example strategy executable by a controller to start an engine is shown. In step  300 , the routine determines if EGR is desired. If so, the routine proceeds to step  302 . If not, the routine proceeds to exit. 
         [0020]    In step  302 , the routine determines a desired EGR flow rate based on engine operating conditions. The desired flow rate of EGR to the engine is predetermined and stored in a table or function in the memory of engine controller  12 ,  FIG. 1 , for example. The table is indexed by engine speed and load (i.e., the engine air charge amount relative to the theoretical engine air charge capacity at standard temperature and pressure). After retrieving the desire EGR flow rate the routine proceeds to step  304 . 
         [0021]    In step  304 , the routine determines if valve number two is active. In this embodiment, orifice number two has a higher flow capacity than orifice number one. However, at lower flow rates, flow variation increases for the higher capacity orifice and valve. Therefore, the lower capacity orifice, orifice number one, is used with valve number one while the desired EGR is in a low range. If orifice number two and valve number two are active, the routine proceeds to step  310 . Otherwise, the routine proceeds to step  306 . 
         [0022]    In step  306 , the routine determines if the desired EGR flow rate is greater than the capacity of orifice number one. That is, the routine determines if the desired flow rate is approaching the orifice sonic flow rate. If yes, the routine proceeds to step  308 . If not, the routine proceeds to step  314 . 
         [0023]    In step  314 , the routine controls EGR valve number one to deliver the desired EGR flow rate. 
         [0024]    In one example, engine controller  12 ,  FIG. 1 , determines the pressure ratio across orifice number one by making an inquiry of differential pressure sensor  265 . Differential pressure sensor  265  may output an analog voltage or a digital series of bits (e.g., a word) that represent the differential pressure across orifice number one. Further, differential pressure may be sensed by a single device or by comparing the difference between the outputs of two separate devices. Since valve number two assumes a closed position in this step, one input to the differential pressure sensor is exposed to intake manifold pressure while the other input is exposed to the pressure between orifice number one and valve number one, see  FIG. 2  for example. Bernoulli&#39;s law is applied based on the pressure observed across orifice number one. The actual flow rate through orifice number one is then compared to the desired flow rate to determine if the position of valve number one should be changed so that the actual flow rate through orifice number one matches the desired flow rate determined in step  302 . Specifically, the actual flow rate is subtracted from the desired flow rate to create a flow rate error. The flow rate error can be input to a proportional/integral controller (PI) or other controller variant to adjust the open-loop valve command. Note that the desired flow rate determined in step  302  corresponds to a duty cycle output that is used to drive a linear solenoid. In one example, the duty cycle is a function of desire EGR flow and the pressure ratio between the exhaust manifold and the intake manifold. This duty cycle is used to command the position valve number one. The adjusted open-loop duty cycle (now closed-loop duty cycle) is output to solenoid number one and the routine proceeds to step  300 . Thus, the valve controller can position a first valve located in a first conduit in response to a pressure in a first conduit and a pressure in a second conduit when a second valve located in a second conduit is in a closed position. 
         [0025]    In step  308 , the routine transitions from operating valve number one to operating valve number two. During the transition, valve number one and valve number two are simultaneously open for a brief period. Therefore, the differential pressure observed by sensor  265 ,  FIG. 2 , does not represent the pressure differential across either orifice number one or orifice number two. As such, the valve number one and valve number two are controlled in an open-loop manner. Specifically, valve number one is ramped from an open position to a closed position while valve number two is ramped to an open position. Each valve is ramped at predetermined rates so that flow variation is mitigated. The commanded duty cycle to the control solenoids is determined from the desired EGR flow and the difference between exhaust pressure and intake manifold pressure. Exhaust pressure may be measured or estimated. Intake manifold pressure may be directly measured or may be estimated based on mass air flow observations. The routine proceeds to step  310 . 
         [0026]    In step  310 , the routine determines if the desired EGR flow rate is less than what is desired for flow through orifice number two. If so, the routine proceeds to step  312 . Otherwise, the routine proceeds to step  316 . 
         [0027]    In step  316 , EGR valve number two is controlled. Similar to the control mentioned in step  314 , engine controller  12 ,  FIG. 1 , determines the pressure ratio across orifice number two by making an inquiry of differential pressure sensor  265 . Alternatively, differential pressure may be sensed by a single device or by comparing the difference between the outputs of two separate devices. Since valve number one assumes a closed position in this step, one input to the differential pressure sensor is exposed to intake manifold pressure while the other input is exposed to the pressure between orifice number two and valve number two, see the description of  FIG. 2  for example. Bernoulli&#39;s law is applied based on the pressure observed across orifice number two. The actual flow rate is then compared to the desired flow rate to determine if the position of valve number two should be changed so that the actual orifice number two flow rate matches the desired flow rate determined in step  302 . Specifically, the actual flow rate is subtracted from the desired flow rate to create a flow rate error. Similar to step  314 , the flow rate error is used to adjust the open-loop valve number two command. The adjusted open-loop duty cycle is output to solenoid number two and the routine proceeds to step  300 . Thus, the valve controller can position a second valve located in a second conduit in response to a pressure in a first conduit and a pressure in a second conduit when a first valve located in a first conduit is in a closed position. 
         [0028]    In step  312 , the routine transitions from operating valve number two to operating valve number one. Similar to the transition in step  308 , valve number two and valve number one are simultaneously open for a brief period. Therefore, the differential pressure observed by sensor  265 ,  FIG. 2 , does not represent the pressure differential across either orifice number one or orifice number two. As such, the valve number one and valve number two are again controlled in an open-loop manner. In this condition, valve number two is ramped from an open position to a closed position while valve number one is ramped to an open position. Again, each valve is ramped at predetermined rates so that flow variation is mitigated, and the commanded duty cycle to the control solenoids is determined from the desired EGR flow and the difference between exhaust pressure and intake manifold pressure. The routine proceeds to step  300 . 
         [0029]    As will be appreciated by one of ordinary skill in the art, the routine described in  FIG. 3  may represent one or more of any number of processing strategies such as event-driven, interrupt-driven, multi-tasking, multi-threading, and the like. As such, various steps or functions illustrated may be performed in the sequence illustrated, in parallel, or in some cases omitted. Likewise, the order of processing is not necessarily required to achieve the objects, features, and advantages described herein, but it is provided for ease of illustration and description. Although not explicitly illustrated, one of ordinary skill in the art will recognize that one or more of the illustrated steps or functions may be repeatedly performed depending on the particular strategy being used. 
         [0030]    This concludes the description. The reading of it by those skilled in the art would bring to mind many alterations and modifications without departing from the spirit and the scope of the description. For example, I3, I4, I5, V6, V8, V10, and V12 engines operating in natural gas, gasoline, diesel, or alternative fuel configurations could use the present description to advantage.