Abstract:
A vehicle control system regulates oxides of nitrogen levels in vehicle emissions. Recirculation of exhaust gas in an engine is controlled with an exhaust gas regulator valve and/or a cam phaser. An oxides of nitrogen sensor determines the level of oxides of nitrogen levels in the exhaust gas and communicates the information to a vehicle controller. The controller determines if the oxides of nitrogen levels are within a predetermined threshold according to a lookup table. The controller adjusts the valve and/or cam phaser if the oxides of nitrogen levels are not within the threshold.

Description:
FIELD OF THE INVENTION 
     The present invention relates to emissions control systems for vehicles, and more particularly to emissions control systems that reduce oxides of nitrogen in vehicle emissions. 
     BACKGROUND OF THE INVENTION 
     Vehicle engines produce oxides of nitrogen (NOx) as a component of vehicle emissions. In particular, lean-burn gasoline and diesel engines tend to produce higher levels of NOx than conventional gasoline engines. 
     In an effort to reduce NOx levels in vehicle emissions, manufacturers employ emissions control systems with engine sensors and NOx storage catalysts. The NOx storage catalysts absorb and decompose the NOx with combustible gases such as carbon monoxide (CO) or hydrocarbon (HC). While reducing NOx levels, these systems tend to increase the level of hydrocarbons in vehicle emissions. 
     Recent designs in NOx sensors allow improved reduction of NOx emissions. NOx sensors may be integrated in the NOx storage catalyst. The NOx sensor detects NOx concentrations in emissions. The sensor communicates with an engine control system and provides data regarding NOx levels. The engine control system takes actions to reduce the NOx levels. 
     SUMMARY OF THE INVENTION 
     A control system regulates vehicle emissions with a valve that controls recirculation of exhaust gas in an engine. A sensor communicates with the exhaust gas to measure oxides of nitrogen levels in the exhaust gas. A controller communicates with the sensor and the valve. The processor adjusts the valve if the oxides of nitrogen levels are not within a threshold. 
     In another feature of the invention, a control system regulates vehicle emissions with a cam phaser that controls recirculation of exhaust gas in an engine. A sensor communicates with the exhaust gas to measure oxides of nitrogen levels in the exhaust gas. A controller communicates with the sensor and the cam phaser. The processor adjusts the cam phaser if the oxides of nitrogen levels are not within a threshold. 
     In another feature of the invention, a calibration map is generated on the controller. The calibration map is a predetermined lookup table that determines the threshold based on an accelerator position and an engine speed. The processor adjusts the valve and/or cam phaser according to the lookup table. 
     Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
         FIG. 1A  is a block diagram of an engine control system providing exhaust gas recirculation using an exhaust gas recirculation (EGR) valve according to prior art; 
         FIG. 1B  is a block diagram of an engine control system providing exhaust gas recirculation using a cam phaser according to prior art; 
         FIG. 2  is a block diagram of an engine control system including a NOx sensor; and 
         FIG. 3  is a block diagram of an engine control system according to the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The following description of the preferred embodiment(s) is merely exemplary in nature and is in no way intended to limit the invention, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. 
     Referring now to  FIG. 1A , an engine controller  10  monitors and adjusts engine performance based on various input signals. For example, the controller  10  may modulate an exhaust gas recirculation (EGR) valve  12  to reduce NOx emissions. Higher combustion temperatures in the engine  14  increase levels of NOx emissions in exhaust gas  16 . Directing some of the exhaust gas  16  back into the engine  14  with intake air  18  reduces the combustion temperatures. The EGR valve  12  meters the amount of exhaust gas  16  that is recirculated with the intake air  18 . The recirculated exhaust gases lower the combustion temperatures, which reduces NOx emissions. The calculation of the valve position for the EGR valve  12  is estimated based on engine conditions such as engine speed and desired air per cylinder. The valve position calculation is not directly related to the actual NOx level. 
     Alternatively, a cam phaser  22  may be incorporated with the engine  14  to reduce NOx emissions, as shown in FIG.  1 B. The cam phaser  22  changes a phase of a camshaft in the engine  14 , which draws the exhaust gas  16  back into the engine  14 . The cam phaser  22  simulates the function of an EGR system by reintroducing the exhaust gas  16  into the engine  14 , which reduces the combustion temperature and NOx emissions. The controller  10  manages phase settings of the cam phaser  22 . As with an EGR system, the phase setting of the cam phaser  22  is an estimation that is derived from engine conditions and is not directly related to the actual NOx level. 
     Referring now to  FIG. 2 , an engine control system  30  is shown. The controller  10  communicates with various components of the engine control system  30 , including but not limited to a throttle position sensor  32  (TPS), a fuel system  34 , an ignition system  36 , and the engine speed sensor  34  (RPM). The controller  10  receives a mass airflow from the MAF  40  and uses the information to determine airflow into the engine  14 . The airflow data is then used to calculate fuel delivery from the fuel system  34  to the engine  14 . The controller  10  further communicates with the ignition system  18  to determine ignition spark timing. The controller  10  may receive additional inputs from other components in the engine control system  8 , including a mass airflow sensor (MAF)  40  and an accelerator pedal  42 . 
     In an EGR system, a conduit  44  connects the exhaust manifold  46  to the intake manifold  48 . The EGR valve  12  that is positioned along the conduit  44  meters EGR according to input from the controller  10 . Alternatively, the cam phaser  22  operates according to input from the controller  10  to simulate an EGR system. In the preferred embodiment, a NOx sensor  50  measures NOx levels and communicates the data to the controller  10 . The controller  10  may communicate with the EGR valve  12  or the cam phaser  22  in response to the data from the NOx sensor  50 . The controller  10  adjusts the EGR valve  12  and/or the cam phaser  22  to correct performance thereof. For example, the controller  10  selectively adjusts the EGR valve  12  or the cam phaser  22  to meter the exhaust gas directed back into the engine. 
     Referring now to  FIG. 3 , the controller  10  manages data tables such as a desired power table  60 , a desired air throttle position table  62 , a desired EGR/cam phaser position table  64 , an expected NOx emission level  66 , and a main spark table  68 . These tables determine the parameters for various engine operations using predetermined lookup tables, as will be described below. 
     The desired power table  60  calculates desired airflow into the engine. Inputs for the desired power table  60  include an accelerator pedal position signal  70  from the accelerator pedal  42  and an rpm signal  72  from the engine speed sensor  38 . A desired airflow signal  74  is divided by the rpm signal  72  to determine a desired air per cylinder signal  76 . The desired air per cylinder signal  76  and the rpm signal  72  are inputs for the desired air throttle position table  62 , the desired EGR/cam phaser position table  64 , and the expected NOx emission level table  66 . 
     The mass airflow sensor  40  outputs a measured power signal  78 . The measured power signal  78  is divided by the rpm signal  72  to determine a measured air per cylinder signal  80 . The rpm signal  72  and the measured air per cylinder signal  80  are inputs for the main spark table  68 . 
     The desired air throttle position table  62  determines a position of a throttle  82  based on the desired air per cylinder  76  and rpm  72  input signals. The throttle  82  controls the amount of air input to the engine. The desired EGR and/or cam phaser table  64  adjusts an EGR and/or cam phaser actuator position based on the input signals. 
     Still referring to  FIG. 3 , the expected NOx emission level  66  is a calibration map that generates target levels for NOx emissions according to various vehicle conditions. The target NOx level from the calibration map is compared to a measured NOx emission level from the NOx sensor  50  to determine a NOx error. The NOx error is communicated to the controller  10  whereby the NOx error may be used for control purposes such as diagnoses and remedial action. For example, the calibration map may specify a preferred range for NOx error. If the NOx error is outside the specified range, the controller  10  adjusts an EGR valve or cam phaser actuator  84  to compensate for the NOx error. 
     Alternatively, the controller  10  may communicate with the desired power table  60 , the desired air throttle position table  62 , or the main spark table  68  to make adjustments in response to the NOx error. For example, the controller  10  may alter the main spark table  68  to adjust spark timing to optimize combustion, further affecting NOx levels. Additionally, the controller  10  may alter the desired air throttle position table  62  to adjust the flow of intake air. 
     The controller  10  may also diagnose the performance of the actuator  84 . If the NOx error is outside of the range specified by the calibration map, the controller  10  may determine that the actuator  70  is malfunctioning. For example, the controller  10  may observe that the NOx error remains outside of the specified range despite remedial action taken by the controller  10  and the various data tables. In this situation, the controller  10  flags the actuator as faulty and in need of maintenance. 
     Those skilled in the art can now appreciate from the foregoing description that the broad teachings of the present invention can be implemented in a variety of forms. Therefore, while this invention has been described in connection with particular examples thereof, the true scope of the invention should not be so limited since other modifications will become apparent to the skilled practitioner upon a study of the drawings, the specification and the following claims.