Abstract:
A control system and method for operating an engine includes a spark ignited (SI) control module controlling the engine in a spark ignited mode, a pre-homogeneous charge compression (HCCI) module controlling the engine in an HCCI mode after the spark ignited mode, and an HCCI module controlling the engine in an HCCI mode after the pre-HCCI mode. The SI module controls the engine in the SI mode after the HCCI mode.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims the benefit of U.S. Provisional Application No. 61/036,280, filed on Mar. 13, 2008. The disclosure of the above application is incorporated herein by reference in its entirety. 
     
    
     FIELD OF THE INVENTION 
       [0002]    The present invention relates to engine control systems, and more particularly to engine control systems for engines operating in both spark ignition and homogenous charge compression ignition (HCCI) modes. 
       BACKGROUND OF THE INVENTION 
       [0003]    The background description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description that may not otherwise qualify as prior art at the time of filing, are neither expressly nor impliedly admitted as prior art against the present disclosure. 
         [0004]    Engines may be operated in a spark ignition (SI) mode and a homogeneous charge compression ignition (HCCI) mode. The HCCI mode involves compressing a mixture of fuel and an oxidizer to a point of auto-ignition. One of the modes may be selected based on engine speed and load. In the HCCI mode, ignition occurs at several locations at a time, which makes a fuel/air mixture burn nearly simultaneously. The HCCI mode performs close to an ideal Otto cycle, provides improved operating efficiency and generates lower emission levels as compared to SI mode. However since there is no direct initiator of combustion, the ignition process tends to be more difficult to control. 
         [0005]    To adjust operation during the HCCI mode, a control system may alter the conditions that induce combustion. For example, the control system may adjust compression ratios, induced gas temperature, induced gas pressure, or the quantity of retained or reinducted exhaust. Several approaches have been used to perform the adjustments and thus extend the HCCI operating region. 
         [0006]    One control approach employs variable valve timing to adjust the compression ratio. For example, the compression ratio can be controlled by adjusting when intake valves close. The amount of exhaust gas retained in a combustion chamber can be controlled by valve re-opening and/or valve overlap. 
         [0007]    Another approach uses a “2-step” intake valve lift approach, which includes switching intake valve modes between a HIGH lift state and a LOW lift state. During the HIGH lift state, the intake valves are lifted to a HIGH level to allow for an amount of air to enter the corresponding cylinders. During the LOW lift state, the intake valves are lifted to a LOW level with a shorter duration, which allows a smaller amount of air to enter the corresponding cylinders relative to the HIGH lift state. 
         [0008]    Without compensation, the 2-step valve lift approach tends to have abrupt and non-uniform transitions between SI and HCCI modes. In other words, there may be undesirable torque disturbances during the transitions. 
       SUMMARY 
       [0009]    The engine control system according to the present disclosure operates the gasoline engine in the SI mode and the HCCI mode. The HCCI mode reduces fuel consumption but is only available over a limited range of engine torques and speeds. 
         [0010]    In one aspect of the disclosure, a method of controlling an engine includes changing engine control from an spark ignited (SI) mode to a pre-homogeneous charge compression (HCCI) mode, changing engine control from the pre-HCCI mode to an HCCI mode and changing engine control from the HCCI mode to the SI mode. 
         [0011]    In another aspect of the disclosure, a control system for an engine includes a spark ignited (SI) control module controlling the engine in a spark ignited mode, a pre-homogeneous charge compression (HCCI) module controlling the engine in an HCCI mode after the spark ignited mode, and an HCCI module controlling the engine in an HCCI mode after the pre-HCCI mode. The SI module controls the engine in an SI mode after the HCCI mode. 
         [0012]    Further areas of applicability will become apparent from the description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0013]    The present invention will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0014]      FIG. 1A  is a functional block diagram of an engine control system that operates in Si and HCCI combustion modes according to the present disclosure; 
           [0015]      FIG. 1B  is a functional block diagram of an exemplary valve lift adjustment system; 
           [0016]      FIG. 1C  is a functional block diagram of an exemplary engine control module; 
           [0017]      FIG. 2  illustrates steps of a method for transitioning from the SI mode to a pre-HCCI mode; 
           [0018]      FIG. 3  illustrates steps of a method for transitioning from the pre-HCCI mode to the HCCI mode; and 
           [0019]      FIG. 4  illustrates steps of a method for transitioning from the HCCI mode to the SI mode. 
       
    
    
     DETAILED DESCRIPTION 
       [0020]    The following description is merely exemplary in nature and is in no way intended to limit the disclosure, its application, or uses. For purposes of clarity, the same reference numbers will be used in the drawings to identify similar elements. As used herein, the phrase at least one of A, B, and C should be construed to mean a logical (A or B or C), using a non-exclusive logical or. It should be understood that steps within a method may be executed in different order without altering the principles of the present disclosure. 
         [0021]    As used herein, the term module refers to an Application Specific Integrated Circuit (ASIC), an electronic circuit, a processor (shared, dedicated, or group) and memory that execute one or more software or firmware programs, a combinational logic circuit, and/or other suitable components that provide the described functionality. 
         [0022]    The engine control system according to the present disclosure operates the gasoline engine in the SI mode and the HCCI mode. The HCCI mode reduces fuel consumption but is only available over a limited range of engine torques and speeds. For example only, the engine control system may operate the engine in the HCCI mode at low to mid loads and low to mid engine speeds. The engine control system may operate the engine in the SI mode at other loads and engine speeds. The HCCI operating zones may be defined by operating maps in calibration tables. 
         [0023]    The engine may be a direct injection gasoline engine and may be selectively operated in a stratified operating mode during the transitions. To operate in the stratified operating mode, the fuel injectors inject the fuel into an area of the cylinder, often a small “sub-cylinder” at the top, or periphery, of the main cylinder. This approach provides a rich charge in that area that ignites easily and burns quickly and smoothly. The combustion process proceeds to a very lean area (often only air) where the flame-front cools rapidly and nitrogen oxides (NO x ) have little opportunity to form. The additional oxygen in the lean charge also combines with carbon monoxide (CO) to form carbon dioxide (CO 2 ). 
         [0024]    Transitions between the SI mode and the HCCI mode should appear seamless to the driver, minimize engine emissions and minimize fuel consumption losses. 
         [0025]    During HCCI operation, the intake manifold pressure may be near atmospheric pressure. Transitions into and out of HCCI involve changes to intake manifold pressure and valve lift. These changes tend to cause sudden changes in air charge supplied to the cylinders. As a result, undesirable changes in engine torque will occur if not properly managed. 
         [0026]    The present disclosure describes control systems and methods for transitioning between the SI mode and the HCCI and vice versa. For example only, the present disclosure describes SI to HCCI mode transitions that employ volume matching using cam phasers, spark retard and/or lean operation during the transition for torque smoothing. Immediate HCCI-SI transitions may be performed from any operating mode with option of spark retard and/or lean operation during the transition for torque smoothing. Coordinated switching of valve lift, MAP, fuel, spark, and phaser control modes may be performed during the transitions. The present disclosure also describes event-based coordination of fueling and spark to expected cam lift. Transition switching duration limitations are used to prevent latching in transition states. 
         [0027]    Referring now to  FIG. 1A , a functional block diagram of an exemplary engine system  100  is presented. The engine system  100  includes an engine  102  that combusts an air/fuel mixture to produce drive torque for a vehicle based on a driver input module  104 . The engine may be a direct ignition engine. Air is drawn into an intake manifold  110  through a throttle valve  112 . An engine control module (ECM)  114  commands a throttle actuator module  116  to regulate opening of the throttle valve  112  to control the amount of air drawn into the intake manifold  110 . 
         [0028]    Air from the intake manifold  110  is drawn into cylinders of the engine  102 . While the engine  102  may include multiple cylinders, for illustration purposes, a single representative cylinder  118  is shown. For example only, the engine  102  may include 2, 3, 4, 5, 6, 8, 10, and/or 12 cylinders. 
         [0029]    Air from the intake manifold  110  is drawn into the cylinder  118  through an intake valve  122 . The ECM  114  controls the amount of fuel injected by a fuel injection system  124 . The fuel injection system  124  may inject fuel into the intake manifold  110  at a central location or may inject fuel into the intake manifold  110  at multiple locations, such as near the intake valve of each of the cylinders. Alternatively, the fuel injection system  124  may inject fuel directly into the cylinders. 
         [0030]    The injected fuel mixes with the air and creates the air/fuel mixture in the cylinder  118 . A piston (not shown) within the cylinder  118  compresses the air/fuel mixture. Based upon a signal from the ECM  114 , a spark actuator module  126  energizes a spark plug  128  in the cylinder  118 , which ignites the air/fuel mixture. The timing of the spark may be specified relative to the time when the piston is at its topmost position, referred to as to top dead center (TDC). 
         [0031]    The combustion of the air/fuel mixture drives the piston down, thereby driving a rotating crankshaft (not shown). The piston then begins moving up again and expels the byproducts of combustion through an exhaust valve  130 . The byproducts of combustion are exhausted from the vehicle via an exhaust system  134 . 
         [0032]    The intake valve  122  may be controlled by an intake camshaft  140 , while the exhaust valve  130  may be controlled by an exhaust camshaft  142 . In various implementations, multiple intake camshafts may control multiple intake valves per cylinder and/or may control the intake valves of multiple banks of cylinders. Similarly, multiple exhaust camshafts may control multiple exhaust valves per cylinder and/or may control exhaust valves for multiple banks of cylinders. The lift actuator module  120  may switch between high and low lift on their exhaust and/or intake valves. 
         [0033]    The time at which the intake valve  122  is opened may be varied with respect to piston TDC by an intake cam phaser  148 . The time at which the exhaust valve  130  is opened may be varied with respect to piston TDC by an exhaust cam phaser  150 . A phaser actuator module  158  controls the intake cam phaser  148  and the exhaust cam phaser  150  based on signals from the ECM  114 . Additionally, the lift actuator module controls the amount of lift, which may be adjusted hydraulically or using other methods. 
         [0034]    The engine system  100  may include an exhaust gas recirculation (EGR) valve  170 , which selectively redirects exhaust gas back to the intake manifold  110 . The engine system  100  may measure the speed of the crankshaft in revolutions per minute (RPM) using an RPM sensor  180 . The temperature of the engine coolant may be measured using an engine coolant temperature (ECT) sensor  182 . The ECT sensor  182  may be located within the engine  102  or at other locations where the coolant is circulated, such as a radiator (not shown). 
         [0035]    The pressure within the intake manifold  110  may be measured using a manifold absolute pressure (MAP) sensor  184 . In various implementations, engine vacuum may be measured, where engine vacuum is the difference between ambient air pressure and the pressure within the intake manifold  110 . The mass of air flowing into the intake manifold  110  may be measured using a mass air flow (MAF) sensor  186 . 
         [0036]    The ECM  114  may calculate measured air per cylinder (APC) based on the MAF signal generated by the MAF sensor  186 . The ECM  114  may estimate desired APC based on engine operating conditions, operator input or other parameters. 
         [0037]    The throttle actuator module  116  may monitor the position of the throttle valve  112  using one or more throttle position sensors (TPS)  190 . The ambient temperature of air being drawn into the engine system  100  may be measured using an intake air temperature (IAT) sensor  192 . The ECM  114  may use signals from the sensors to make control decisions for the engine system  100 . 
         [0038]    To abstractly refer to the various control mechanisms of the engine  102 , each system that varies an engine parameter may be referred to as an actuator. For example, the throttle actuator module  116  can change the blade position, and therefore the opening area, of the throttle valve  112 . The throttle actuator module  116  can therefore be referred to as an actuator, and the throttle opening area can be referred to as an actuator position. 
         [0039]    Similarly, the spark actuator module  126  can be referred to as an actuator, while the corresponding actuator position is amount of spark advance or retard. Other actuators include the EGR valve  170 , the phaser actuator module  158 , the fuel injection system  124 , and the lift actuator module  120 . The term actuator position with respect to these actuators may correspond to manifold absolute pressure, EGR valve opening, intake and exhaust cam phaser angles, and air/fuel ratio, respectively. 
         [0040]    Referring now to  FIG. 1B , a functional block diagram of a valve lift control circuit  250  is shown. The valve lift control circuit  250  includes an intake/exhaust valve assembly  252  that receives oil from an oil reservoir  254  via an oil pump  256 . The oil is filtered through an oil filter  258  prior to reception by the valve assembly  252 . The control module controls lift operation of intake and exhaust valves  260 ,  262  of the valve assembly  252 . 
         [0041]    The valve assembly  252  includes the intake and exhaust valves  260 ,  262 , which have open and closed states and are actuated via one or more camshafts  264 . A dedicated intake camshaft and a dedicated exhaust camshaft may be included. In another embodiment, the intake and exhaust valves  260 ,  262  share a common camshaft. When in an open state the intake and exhaust valves  260 ,  262  may be operating in various lift states. 
         [0042]    The valve assembly  252  also includes valve lift state adjustment devices  270 . The lift state adjustment devices  270  may include oil pressure control valves  272  and valve lift control valves, such as solenoids  274 . Other lift state adjustment devices  276 , such as lift pins, levers, rockers, springs, locking mechanisms, tappets, etc may be included. 
         [0043]    The valve lift control circuit  250  may include an oil temperature sensor  280  and/or an oil pressure sensor  282 . The control module signals the oil pressure control valves  272  based on temperature and pressure signals received from the temperature and pressure sensors  280 ,  282 . 
         [0044]    Referring now to  FIG. 1C , the engine control module  114  may comprise a map control module  290  having a MAP control mode (MM). The MM can be set to SI and HCCI modes. The engine control module  114  comprises a fuel delivery module  292  having a fuel delivery mode (FM). The fuel delivery module  292  may switch the FM between SI, stratified and HCCI modes. The fuel delivery module  292  may determine the manner, timing and/or amount of fuel delivery. 
         [0045]    The engine control module  114  comprises a combustion control module  294  having a combustion mode (CM). The combustion module  294  may switch the CM between SI, HCCI and pre-HCCI modes and include an SI control module  294 ( a ), a pre HCCI control module  294 ( b ) and an HCCI control module  294 ( c ). 
         [0046]    The engine control module  114  comprises a spark delivery module  296  having a spark delivery mode (SM). The spark delivery module  296  may switch the SM between SI, SI with retard, stratified and HCCI modes. The spark delivery module  296  may determine the timing and duration of spark. 
         [0047]    The engine control module  114  comprises a fuel calculation module  297  having a fuel calculation mode (FC). The fuel calculation module  297  may switch the FC between air lead and fuel lead modes. In air lead mode, fuel is controlled based on air. In fuel lead mode, air is controlled based on the measured or delivered fuel. 
         [0048]    The engine control module  114  comprises a phaser control module  298  having a phaser control mode (PM). The phaser control module  298  may switch the PM between SI and HCCI modes. The phaser control module  298  may determine cam phasing. 
         [0049]    The engine control module  144  comprises a lift control module  299  having a lift control mode (LM). The lift control module  299  may switch the LM between high and low valve lift modes. 
         [0050]    Referring now to  FIGS. 2 and 3 , when transitioning from the SI mode to the HCCI mode, the control system first transitions from the SI mode to a pre-HCCI mode ( FIG. 2 ) and then from pre-HCCI mode to the HCCI mode ( FIG. 3 ). 
         [0051]    In  FIG. 2 , the transition from the SI mode to the pre-HCCI mode is shown. In step  400 , control initiates a transition from the SI mode to the pre-HCCI mode. In step  404 , control determines whether volume match is enabled. If step  404  is true, control continues with step  408  and sets the map control mode (MM) equal to volume match mode and the phaser control mode (PM) equal to the volume match mode. When volume matching is enabled, the cam phasers are used to match air charge as the lift state of the intake and/or exhaust valves are switched such as from the high lift state to the low lift state. This transition changes the air charge that may be partially offset by using the cam phaser position, which will minimize torque disturbances. 
         [0052]    In step  412 , control determines whether volume match occurred or a predetermined timer period is up. If step  412  is true, control continues with step  414  and sets the combustion mode (CM) equal to the Pre-HCCI mode. In step  416 , the engine operating mode is set equal to Pre-HCCI mode. 
         [0053]    If step  404  is false and volume matching is not enabled, control continues with step  420  and sets the map control mode (MM) to transition from the desired SI MAP to the desired HCCI MAP. Desired MAP (MAP_des) is set equal to MAP_HCCI. In  FIG. 2 , MM=SI-HCCI refers to transitioning MAP from the SI MAP value to the HCCI MAP value. Alternately, a separate calibration between the SI value and the HCCI value may be used. These values may be accessed using a lookup table. 
         [0054]    In step  422 , control compares MAP to a first MAP threshold (MAP TH   1 ). If MAP is not greater than MAP TH     —     1 , control continues with step  426  and sets the phaser control mode (PM) to the SI mode. If step  422  is true, control sets the phaser control mode (PM) to transition from the SI mode to the HCCI mode. Control continues from steps  426  and  428  with step  430 . 
         [0055]    In step  430 , control determines whether MAP is greater than a second MAP threshold MAP TH     —     2  before a predetermined timeout occurs. If step  430  is true, control continues with step  414 . If steps  430  or  412  are false, control continues with step  434 . In step  434 , control determines whether stratified fuel is enabled and air per cylinder (APC)/F strat  is greater than a minimum threshold. In other words, the APC divided by stratified fuel (or air to fuel (A/F) ratio) is greater than a minimum threshold. 
         [0056]    If step  434  is false, control sets the fuel delivery mode (FM) to SI mode, the spark delivery mode (SM) to SI mode with retard, and the fuel calculation mode (FC) is set to air lead mode in step  438 . In other words, torque is being controlled with spark retard at this point. 
         [0057]    If step  434  is true, control sets the fuel delivery mode (FM) to stratified, the spark delivery mode (SM) to stratified, and the fuel calculation mode (FC) to fuel lead mode in step  440 . Control continues from steps  438  and  440  with step  444  where control sets the combustion mode (CM) to transition from the SI mode to the HCCI mode. 
         [0058]    Referring now to  FIG. 3 , a method for transitioning from the pre-HCCI mode to the HCCI mode is shown. Control begins with step  450  when a transition from Pre-HCCI mode to HCCI mode is needed. This occurs whenever the engine operating mode transitions to the pre-HCCI mode. In step  454 , control sets MAP_des equal to MAP_HCCI and control commands low lift with LM=Low Lift. 
         [0059]    In step  456 , control determines whether the low lift state has been achieved by the intake and/or exhaust valves. If step  456  is true, control determines whether the stratified fuel option is enabled in the low-lift state and whether a predetermined number or limit of engine events occurs (such as combustion events). If step  460  is false, control sets the fuel delivery mode (FM), the spark delivery mode (SM), the phaser control mode (PM), the map control mode (MM), and the combustion mode (CM) to the HCCI mode and the fuel calculation mode (FC) to the fuel lead mode. Control continues with step  466  and sets the engine operating mode equal to the HCCI mode. 
         [0060]    If step  460  is true, control sets the fuel delivery mode (FM) and the spark delivery mode (SM) to the stratified mode and the fuel calculation mode (FC) to fuel lead mode. Control continues from step  470  with step  472  where control sets the combustion mode (CM) equal to the pre-HCCI mode. Control returns from step  472  with step  456 . 
         [0061]    If step  456  is false, control continues with step  474 , determines whether the stratified fuel is in the high-lift state and determines whether a predetermined number (or limit) of engine events has occurred (such as combustion events). If step  474  is false, control continues with step  478  and sets the fuel delivery mode (FM) equal to the SI mode, the spark delivery mode (SM) equal to the SI mode with retard, and the fuel calculation mode (FC) equal to the air lead mode. If step  474  is true, control sets the fuel delivery mode (FM) and the spark delivery mode (SM) equal to the stratified mode and the fuel calculation mode (FC) to the fuel lead mode. Control continues from steps  478  and  474  with step  472 . 
         [0062]    Referring now to  FIG. 4 , a method for transitioning from the HCCI mode to the SI mode is shown. When the transition from the HCCI mode to the SI mode is requested in step  500 , control continues with step  504  and commands the high-lift state with LM=High. Control sets the map control mode (MM) and the combustion mode (CM) to transition from the HCCI mode to the SI mode. 
         [0063]    In step  508 , control determines whether the high lift state has been achieved. If step  508  is false, control continues with step  512  and determines whether stratified fuel for low lift is true. If step  512  is true, control sets the fuel delivery mode (FM) and the spark delivery mode (SM) equal to the stratified mode. If step  512  is false, control sets the fuel delivery mode (FM) and the spark delivery mode (SM) to the HCCI mode. Control continues from step  516  and  520  with step  518  and sets the fuel calculation mode (FC) to fuel lead mode and the phaser control mode (PM) to transition from the HCCI mode to the SI mode. Control continues with step  508 . 
         [0064]    If step  508  is true, control sets MAP_des=MAP_SI and the phaser control mode (PM) to the SI mode. In step  530 , control determines whether a MAP threshold is met or a predetermined timeout occurred. If step  530  is false, control continues with step  534  and determines whether stratified fuel for highlift state is true and APC/F strat  is greater than a minimum threshold. 
         [0065]    If step  534  is true, control continues with step  538  and sets the fuel delivery mode (FM) and the spark delivery mode (SM) to the stratified mode and the fuel calculation mode (FC) to the fuel lead mode. Control continues with step  508 . If step  534  is false, control sets the fuel delivery mode (FM) to the SI mode, the spark delivery mode (SM) to the SI mode w/retard, and the fuel calculation mode (FC) to the air lead mode. Control continues with step  508 . 
         [0066]    If step  530  is true, control continues to step  540  and turns the map control mode (MM) off and the combustion mode (CM) to the SI mode and fuel calculation mode to air lead mode. In step  544 , control sets the engine operating mode equal to SI. 
         [0067]    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.