Abstract:
A control system for a homogeneous charge compression ignition (HCCI) engine includes a timing adjustment module and a combustion control module. The timing adjustment module, per combustion event, advances timings of N fuel injections and retards timings of M fuel injections and spark during a transition from HCCI combustion to mixed-mode combustion. The combustion control module subsequently retards the timings of the N fuel injections and advances the timings of the M fuel injections and the spark to desired timings, respectively, wherein the N fuel injections and the M fuel injections occur sequentially during each combustion event of the HCCI engine, and wherein N and M are integers greater than or equal to zero.

Description:
FIELD 
       [0001]    The present disclosure relates to homogeneous charge compression ignition (HCCI) engines, and more particularly to a system and method for controlling fuel injection timing and spark timing during transitions between combustion modes of HCCI engines. 
       BACKGROUND 
       [0002]    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. 
         [0003]    Internal combustion engines draw air into an intake manifold through an inlet system that may be regulated by a throttle. The air in the intake manifold may be distributed to a plurality of cylinders and combined with fuel to create an air/fuel (A/F) mixture. The fuel may be provided via a plurality of fuel injectors located at intake ports of the cylinders (i.e., port fuel injection) or in the cylinders (i.e., direct fuel injection). The A/F mixture may be compressed by pistons and combusted within the cylinders to drive the pistons and rotatably turn a crankshaft generating drive torque. 
         [0004]    Homogeneous charge compression ignition (HCCI) engines may operate in a plurality of combustion modes depending on operating conditions (e.g., engine load). The plurality of combustion modes may include HCCI combustion, spark ignition (SI) combustion, and mixed-mode combustion (e.g., a combination of HCCI and SI combustion). More specifically, for example, HCCI engines may operate via mixed-mode combustion at low engine loads, HCCI combustion at medium engine loads, and SI combustion at high engine loads. 
         [0005]    SI combustion includes compressing the A/F mixture and igniting the compressed A/F mixture via spark from spark plugs. HCCI combustion, on the other hand, includes compressing the A/F mixture until a critical pressure and/or temperature is reached and the A/F mixture automatically combusts. Mixed-mode combustion, as previously stated, includes a combination of HCCI combustion and SI combustion. More specifically, mixed-mode combustion includes HCCI combustion plus “assisting” the combustion of the A/F mixture via spark from spark plugs. 
       SUMMARY 
       [0006]    A control system for a homogeneous charge compression ignition (HCCI) engine includes a timing adjustment module and a combustion control module. The timing adjustment module, per combustion event, advances timings of N fuel injections and retards timings of M fuel injections and spark during a transition from HCCI combustion to mixed-mode combustion. The combustion control module subsequently retards the timings of the N fuel injections and advances the timings of the M fuel injections and the spark to desired timings, respectively, wherein the N fuel injections and the M fuel injections occur sequentially during each combustion event of the HCCI engine, and wherein N and M are integers greater than or equal to zero. 
         [0007]    A method for controlling a homogeneous charge compression ignition (HCCI) engine includes, per combustion event, advancing timings of N fuel injections and retarding timings of M fuel injections and spark during a transition from HCCI combustion to mixed-mode combustion, and subsequently retarding the timings of the N fuel injections and advancing the timings of the M fuel injections and the spark to desired timings, respectively, wherein the N fuel injections and the M fuel injections occur sequentially during each combustion event of the HCCI engine, and wherein N and M are integers greater than or equal to zero. 
         [0008]    In still other features, the systems and methods described above are implemented by a computer program executed by one or more processors. The computer program can reside on a tangible computer readable medium such as but not limited to memory, nonvolatile data storage, and/or other suitable tangible storage mediums. 
         [0009]    Further areas of applicability of the present disclosure will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the disclosure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0010]    The present disclosure will become more fully understood from the detailed description and the accompanying drawings, wherein: 
           [0011]      FIG. 1  is graphs illustrating a conventional transition between combustion modes of a homogeneous charge compression ignition (HCCI) engine; 
           [0012]      FIG. 2  is a functional block diagram of an exemplary HCCI engine system according to the present disclosure; 
           [0013]      FIG. 3  is a functional block diagram of an exemplary control module according to the present disclosure; 
           [0014]      FIG. 4  is a flow diagram of an exemplary method for controlling fuel injection timing and spark timing during transitions between combustion modes of an HCCI engine according to the present disclosure; and 
           [0015]      FIG. 5  is graphs illustrating exemplary results of controlling fuel injection timing and spark timing during a transition between combustion modes of an HCCI engine according to the present disclosure. 
       
    
    
     DETAILED DESCRIPTION 
       [0016]    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. 
         [0017]    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. 
         [0018]    HCCI engine systems may include exhaust gas recirculation (EGR) systems. EGR systems may introduce exhaust gas produced during combustion into an intake manifold, thereby combining the exhaust gas with fresh air in the intake manifold. For example, EGR may be used to increase efficiency of and/or improve control of HCCI combustion. More specifically, EGR may improve combustion efficiency by decreasing heat transfer loss and may improve control of HCCI combustion by providing for control of a ratio of an air/fuel (A/F) mixture being combusted. 
         [0019]    Moreover, EGR may be more useful at higher engine loads. In other words, an amount (e.g., a percentage) of EGR may increase as engine load increases during HCCI combustion. Therefore, a substantial amount of EGR may be required during high load HCCI combustion (i.e., high load relative to an HCCI combustion operating range). Mixed-mode combustion (e.g., low engine loads), however, may not tolerate EGR. In other words, EGR during mixed-mode combustion may cause combustion problems (e.g., misfires, stalling, etc.), particularly during abrupt (i.e., fast) HCCI to mixed-mode transitions. For example, fast HCCI to mixed-mode transitions may occur when a driver of the vehicle removes his foot from an accelerator pedal. 
         [0020]    Referring now to  FIG. 1 , a transition from HCCI combustion to mixed-mode combustion is illustrated. Specifically, six graphs are shown with respect to time (e.g., in seconds, or s) and from top to bottom represent fuel injection quantity (e.g., in milligrams per second, or mg/s), MAF rate (e.g., in grams per second, or g/s), EGR valve position (e.g., opening percentage, or %), negative valve overlap (NVO, e.g., in crank angle degrees, or CAD), fuel injection and spark timings (e.g., in degrees before top-dead-center, or BTDC), and indicated mean effective pressure (IMEP, e.g., barometric pressure, or Bar), respectively. 
         [0021]    More specifically, the transition occurs when MAF rate (i.e., engine load) decreases below an HCCI combustion threshold. Therefore, EGR is disabled (e.g., an EGR valve is closed) during the transition to mixed-mode combustion. However, exhaust gas may remain in the intake manifold during and/or after the transition. Rather, a relatively small amount of NVO may occur, which may cause combustion problems when conventional fuel injection timing and spark timing are used. For example, the combustion problems (e.g., misfires, stalling, etc.) are illustrated by fluctuations in the IMEP of the cylinders. 
         [0022]    Accordingly, a system and method are presented for controlling fuel injection timing and spark timing during transitions between combustion modes of an HCCI engine. Specifically, the system and method may control fuel injection timing and spark timing to prevent combustion problems during transitions from HCCI combustion to mixed-mode combustion. The system and method may, per combustion event, advance timing of N fuel injections, retard timing of M fuel injections, and retard spark timing. The N and M fuel injections may occur sequentially with the N fuel injections preceding the M fuel injections. For example, N may be two and M may be one (e.g., a total of three fuel injections in each cylinder during each combustion cycle). 
         [0023]    More specifically, the system and method may, per combustion event, advance the timing of the N fuel injections, retard the timing of the M fuel injections, and retard the spark timing to predetermined timings, respectively. The system and method may then retard the timing of the N fuel injections, advance the timing of the M fuel injections, and advance the spark timing to desired timings during a predetermined period. Advancing the timing of the N fuel injections may increase fuel reforming during mixed-mode combustion. Additionally, retarding the timing of the M fuel injections and the spark timing may provide for more robust stratified combustion during the transition from HCCI combustion to mixed-mode combustion. 
         [0024]    Referring now to  FIG. 2 , an engine system  10  includes an HCCI engine  12 . The HCCI engine  12  draws air into an intake manifold  14  through an inlet system  16  that may be regulated by a throttle  22 . For example, the throttle  22  may be electronically controlled (e.g., electronic throttle control, or ETC). A compressor  18  of a turbocharger  20  (also referred to as “turbo  20 ”) may pressurize (i.e., boost) the air drawn into the intake manifold  14 . A MAF sensor  24  may measure the MAF rate through the inlet system  16 . An intake manifold absolute pressure (MAP) sensor  26  measures a pressure of the air inside the intake manifold  14 . The air in the intake manifold  14  may be distributed to a plurality of cylinders  28 . While four cylinders are shown, the HCCI engine  12  may include other numbers of cylinders. 
         [0025]    The air in the cylinders  28  may be mixed with fuel from a plurality of fuel injectors  30  to create an A/F mixture. For example, the fuel injectors  30  may inject the fuel via intake ports of the cylinders  28  (i.e., port fuel injection) or directly into the cylinders  28  (i.e., direct fuel injection). The A/F mixture may be compressed by pistons (not shown) within the cylinders  28 . During HCCI combustion, the A/F mixture may be compressed until the A/F mixture reaches the critical pressure and/or temperature and automatically combusts. The HCCI engine  12 , however, may also include a plurality of spark plugs  32  used for “spark assist” (e.g., during mixed-mode combustion) and/or spark ignition during SI combustion. 
         [0026]    The combustion of the A/F mixture within the cylinders  28  drives pistons (not shown) which rotatably turn a crankshaft  34  generating drive torque. An engine speed sensor  36  may measure a rotational speed of the crankshaft  34  (e.g., in revolutions per minute, or RPM). The drive torque may be transferred from the crankshaft  34  to a driveline  38  (e.g., wheels) of the vehicle via a transmission  40 . The transmission  40  may also be coupled to the crankshaft  34  via a fluid coupling such as a torque converter (not shown). Exhaust gas resulting from combustion may be expelled from the cylinders  28  into an exhaust manifold  42 . 
         [0027]    An exhaust treatment system (ETS)  44  may treat the exhaust gas to reduce emissions before releasing the exhaust gas into the atmosphere. For example, the ETS  44  may include at least one of oxidation catalysts (OCs), NOx absorbers/adsorbers, selective catalytic reduction (SCR) catalysts, particulate matter (PM) filters, and catalytic converters. The exhaust gas may also be recirculated into the intake manifold  14  via an EGR system  46  that includes an EGR line  48  and an EGR valve  50 . In other words, the EGR line  48  may connect the exhaust manifold  42  to the intake manifold  14  and the EGR valve  50  may regulate an amount of exhaust gas introduced into the intake manifold  14 . 
         [0028]    Furthermore, the exhaust gas may be routed through a turbine system  52  that includes a turbine line  54  and a turbine  56  (part of the turbocharger  20 ). The exhaust gas may rotate the turbine  56  before being released into the atmosphere. The exhaust gas, however, may also be treated to decrease emissions (similar to the ETS  44 ) before being released into the atmosphere. The turbine  56  powers the compressor  18  via a shaft  58  of the turbocharger  20 . Moreover, while the EGR system  46  and the turbine system  52  are shown to share a port of the exhaust manifold  42 , the EGR system  46  and the turbine system  52  may have separate ports (and thus a separate EGR line  48  and turbine line  54 ). 
         [0029]    A control module  60  may receive signals from the turbocharger  20 , the throttle  22 , the MAF sensor  24 , the MAP sensor  26 , the fuel injectors  30 , the spark plugs  32 , the engine speed sensor  36 , the transmission  40 , the ETS  44 , and/or the EGR valve  50 . Furthermore, the control module  60  may control the turbocharger  20  (e.g., boost pressure), the throttle  22  (e.g., ETC), the fuel injectors  30 , the spark plugs  32 , the transmission  40 , the ETS  44 , and/or the EGR valve  50 . The control module  60  may also implement the system or method of the present disclosure. 
         [0030]    Referring now to  FIG. 3 , the control module  60  is shown in more detail. The control module  60  may include a transition detection module  80 , a timing adjustment module  84 , and a combustion control module  88 . The control module  60  may also include memory (not shown) for storing predetermined and determined parameters. For example, the memory (not shown) may include non-volatile memory (NVM). 
         [0031]    The transition detection module  80  detects transitions from HCCI combustion to mixed-mode combustion. More specifically, the transition detection module  80  may determine when a load on the HCCI engine  12  decreases below an HCCI operating threshold. In other words, the transition detection module  80  may detect when the engine load decreases from an HCCI operating range to a mixed-mode operating range. For example, the HCCI operating threshold may include a smallest engine load that the HCCI engine  12  may operate via HCCI combustion. The transition detection module  80  receives a signal from the MAF sensor  24  indicating a load on the HCCI engine  12 . The transition detection module  80 , however, may also receive signals indicating other parameters, such as input from the driver of the vehicle. 
         [0032]    The timing adjustment module  84  communicates with the transition detection module  80 . For example, the transition detection module  80  generate a status signal to notify the timing adjustment module  84  that the HCCI engine  12  is transitioning from (or is about to transition from) HCCI combustion to mixed-mode combustion. Thus, the timing adjustment module  84  may then adjust fuel injection timing and spark timing when the status signal is received from the transition detection module  80 . For example, the timing adjustment module  84  may adjust the timings of N and M fuel injections and spark timing. In other words, each combustion cycle may include (N+M) sequential fuel injections followed by spark. For example, N may be an integer greater than or equal to two and M may be an integer greater than or equal to one. For example only, N may be two and M may be one. 
         [0033]    More specifically, the timing adjustment module  84  may advance the timing of the N fuel injections and retard the timing of the M fuel injections and the spark timing. In other words, the timing adjustment module  84  may advance the timing of the N fuel injections, retard the timing of the M fuel injections, and retard the spark timing to predetermined timings. For example, the timing adjustment module  84  may advance the timing of the N fuel injections to predetermined timings t N1 +t NN , and may retard the timing of the M fuel injections and the spark timing to predetermined timings t M1 −t MM  and t S , respectively. 
         [0034]    The combustion control module  88  receives the adjusted timings of the N fuel injections (t N1 +t NN , respectively, also referred to as “N”), the M fuel injections (t M1 −t MM , respectively, also referred to as “M”), and the spark (t S , also referred to as “S”). For example, the timings and the adjusted timings may include degrees (°) of the crankshaft  34  (also known as crank angle degrees, or CAD) before compression top-dead-center (BTDC). The combustion control module  88  may also receive the signal from the MAF sensor  24  indicating the load on the HCCI engine  12 . Furthermore, the combustion control module  88  may also receive other signals indicating other engine operating parameters (e.g., driver input, engine speed, etc.). 
         [0035]    More specifically, the combustion control module  88  may determine desired timings based on the engine load and/or the other engine operating parameters. In other words, the combustion control module  88  may determine the desired timings for mixed-mode combustion. For example, the desired timings may include desired timings for each of the N and M fuel injections (e.g., t DN1 +t DNN , respectively, and t DM1 −t DMM , respectively) and a desired timing for the spark (e.g., t DS ). The combustion control module  88  may initially control fuel injection and spark based on the adjusted timings N, M, and S. The combustion control module  88 , however, may then retard the timing of the N fuel injections and advance the timing of the M fuel injections and the spark timing until the desired timings are reached. 
         [0036]    Specifically, the combustion control module  88  may adjust the timings to the desired timings during a period. For example, the period may be a predetermined period. The period, however, may be based on other parameters (e.g., a duration of the transition between HCCI combustion and mixed-mode combustion). After the combustion control module  88  has retarded the timing of the N fuel injections and advanced the timing M fuel injections and the spark timing to the desired timings, respectively, control may continue during mixed-mode combustion according on the desired injection timing. 
         [0037]    Referring now to  FIG. 4 , a method for controlling fuel injection timing and spark timing during transitions between combustion modes of the HCCI engine  12  begins at  100 . At  100 , the control module  60  may detect whether transition from HCCI combustion to mixed-mode combustion is occurring or is imminent (e.g., within a predetermined period from occurring). If true, control may proceed to  104 . If false, control may return to  100 . 
         [0038]    At  104 , the control module  60  may advance the timings of the N fuel injections. For example, the control module  60  may advance the timings of the N fuel injections to predetermined timings (e.g., t N1 +t NN , respectively). At  108 , the control module  60  may retard the timings of the M fuel injections. For example, the control module  60  may retard the timings of the M fuel injections to predetermined timings (e.g., t M1 −t MM , respectively). At  112 , the control module  60  may retard the spark timing to a predetermined timing (e.g., t S ). Additionally, for example, the predetermined timings may also be based on other parameters (e.g., a speed of the transition from HCCI combustion to mixed-mode combustion). 
         [0039]    After the expiration of the predetermined period, at  116  the control module  60  may then retard the timings of the N fuel injections to desired timings, respectively (e.g., t DN1   + t DNN , respectively). Also, at  120  the control module  60  may then advance the timings the M fuel injections to desired timings, respectively (e.g., t DM1 −t DMM , respectively). Also, at  124  the control module  60  may then advance the spark timing to a desired timing (e.g., t DS ). For example, the desired timings (e.g., t DN1 +t DNN , t DM1 −t DMM , and t DS ) may be based on engine load and other inputs (e.g., driver input, engine speed, etc.). Control may then return to  100 . 
         [0040]    Referring now to  FIG. 5 , exemplary results of the system and/or method of the present disclosure are illustrated. Specifically, six graphs are shown with respect to time (e.g., s) and from top to bottom represent fuel injection quantity (e.g., in mg/s), MAF rate (e.g., g/s), EGR valve position (e.g., opening percentage, or %), NVO (e.g., in CAD), fuel injection and spark timings (e.g., in degrees BTDC), and IMEP (e.g., barometric pressure, or Bar), respectively. 
         [0041]    More specifically and similar to  FIG. 1 , a transition from HCCI combustion to mixed-mode combustion occurs when the MAF rate (i.e., engine load) decreases below the HCCI combustion threshold. Accordingly, EGR is disabled (e.g., an EGR valve is closed) during the transition. However, advancing the timings of the N fuel injections and retarding the timings of the M fuel injections and the spark may decrease the amount of NVO (i.e., compared to the conventional control of  FIG. 1 ). Therefore, no combustion problems (e.g., misfires, stalling, etc.) may occur, as shown by the stable IMEP of the cylinders. 
         [0042]    The broad teachings of the disclosure can be implemented in a variety of forms. Therefore, while this disclosure includes particular examples, the true scope of the disclosure 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.