Abstract:
The present invention relates to a method for controlling an internal combustion engine having a means ( 16 ) for directly injecting fuel as well as a means ( 22 ) for admitting at least one fluid into the combustion chamber, a cylinder ( 12 ), a burned-gas exhaust means ( 28 ), and a processing and control unit ( 48 ) receiving information on at least the driver&#39;s torque demand and the engine speed (Ne), comprising a) determining the desired torque (Torque_des) corresponding in particular to driver demand; b) from this desired torque, determining a desired Indicated Meon Effective Pressure (IMEP_des) from which the parameters (Mair_sp, BGR_sp) are established to control admission of at least one fluid into the combustion chamber; and c) determining a specified value of the IMEP (IMEP_sp) from the desired IMEP and at least one magnitude linked to the fluid admitted into the combustion chamber, to define the fuel injection parameters (Mfuel_i, SOI_i, Pfuel) in the combustion chamber.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     The present invention relates to a method for controlling combustion in an internal combustion engine, particularly a direct-injection engine, and an engine using such a method.  
         [0003]     Such as Diesel engines with burned-gas recirculation, and particularly engines of this type that can operate inn two combustion modes.  
         [0004]     2. Description of the Prior Art  
         [0005]     A traditional combustion mode injects the fuel around the Combustion Top Dead Center with diffusion combustion preferably being used at high loads, while another combustion mode, known as homogenous combustion, is used at low and medium loads.  
         [0006]     In this latter combustion mode, it is known that the fuel coming from an injector can be mixed with the gaseous fluid or fluids admitted into the combustion chamber of this engine, such as air or a mixture of air and recirculated exhaust gas, in order to obtain a homogenous air-fuel mixture before combustion begins.  
         [0007]     This is known, particularly for Diesel engines, by the general term Homogenous Charge Compression Ignition (abbreviated HCCI) and the applicant has developed such a combustion mode using a fuel injector with a small crank angle to avoid wetting the cylinder walls with the injected fuel. This not only prevents degradation of the lubricant present on this wall, but also prevents increases in pollutant emissions and reduction in engine performance, particularly in terms of fuel consumption. Development of this combustion mode is described more precisely in French Patents 2,818,324 and 2,818,325 by the applicant offering such a process used under the name NADI™.  
         [0008]     Moreover, at low and medium loads, this homogeneous combustion mode generates only low flame temperatures upon combustion of the air-fuel mixture in the combustion chamber, which considerably cuts down on nitrogen oxide (Nox) and particle emissions while preserving engine performance.  
         [0009]     To favor such a combustion mode, it is desirable to introduce not only intake air but large quantities of burned gases from the exhaust and to associate this burned gas recirculation with specific fuel injection strategies. The means most commonly used to achieve such recirculation is to send some of the exhaust gases to the engine intake through an external circuit known as EGR (Exhaust Gas Recirculation).  
         [0010]     On the other hand, as already mentioned, such engines are also designed to operate by traditional combustion, which requires more moderate burned-gas levels and different injection strategies from those used in homogeneous combustion.  
         [0011]     The problem encountered with this type of engine operating in two combustion modes resides in the fact that it is difficult to ensure rapid, precise control of the mass of air and/or burned gases admitted into the cylinder as a function of driver demand, because the dynamics of the air loop (burned air and/or gas) are relatively slow, about a few seconds, particularly by comparison to the dynamics of the fuel loop which reacts on the order of the engine combustion cycle. Hence, in a transient operating phase, the air and/or burned-gas settings may be unsuitable for the fuel settings, which is not conducive to optimal combustion in terms of pollutant emissions, combustion noise, or fuel consumption.  
       SUMMARY OF THE INVENTION  
       [0012]     The present invention is a remedy to the above-mentioned drawbacks by a method of achieving optimal combustion while endeavoring to guarantee a torque responsive to driver demand.  
         [0013]     For this purpose, the invention is a method for controlling an internal combustion engine having a means for directly injecting fuel into the combustion chamber, a cylinder, a means for admitting at least one fluid into said chamber, a burned-gas exhaust means, and a processing and control unit receiving information on at least the driver&#39;s torque demand and the engine speed, ecomprising:  
         [0014]     a) determining a desired torque corresponding in particular to driver demand;  
         [0015]     b) from the desired torque, determining a desired from which the parameters are established to control admission of at least one fluid into the combustion chamber;  
         [0016]     c) determining a specified value of the IMEP from the desired IMEP and at least one magnitude linked to the fluid admitted into the combustion chamber, to define a fuel injection parameters in the combustion chamber.  
         [0017]     Preferably, the magnitude can be linked to air introduced into the combustion chamber.  
         [0018]     This magnitude can correspond to the mass of air introduced into the combustion chamber.  
         [0019]     Advantageously, the method may evaluate magnitude by observers.  
         [0020]     This method may determine the specified IMEP value also considering the engine speed.  
         [0021]     Advantageously, the control method may correct the injection by comparing the magnitude linked to the recirculated burned gases and/or the mass of air introduced into this combustion chamber and the reference values of the magnitude established from the specified IMEP.  
         [0022]     This magnitude may be linked to the recirculated burned gases and be estimated by observers.  
         [0023]     In the case of a spark ignition engine, the method may control the ignition parameters from the IMEP specified value.  
         [0024]     This method may correct the ignition parameters according to the gap between the magnitude linked to the recirculated burned gases and/or the mass of air introduced into the combustion chamber and the reference values for this magnitude established from the specified IMEP.  
         [0025]     The invention can also be applied to a direct injection internal combustion engine having at least one cylinder with a combustion chamber having a means for injecting fuel into said combustion chamber, a means for admitting at least one fluid into this combustion chamber, and a burned-gas exhaust means, combustion in said chamber being controlled by a processing and control unit, wherein the unit has a module for controlling the admission parameters of at least one fluid into the combustion chamber, a module for controlling the fuel injection parameters, and an acquisition/specification module for the control modules.  
         [0026]     The invention can also be applied in particular to a Diesel combustion engine.  
         [0027]     The invention can also be applied to an engine having at least one cylinder, a piston sliding in this cylinder, and having a nipple pointing to the cylinder head and disposed in the center of a concave bowl, admission and burned-gas exhaust means, and at least one injector to inject fuel with a crank angle less than or equal to  
       2   ⁢           ⁢   Arctg   ⁢     CD     2   ⁢           ⁢   F           
 
 where CD is the cylinder diameter and F is the distance between the point of origin of the fuel jets coming from the injector and the position of the piston corresponding to a crank angle of 50° C. with respect to the top dead center. 
 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0028]     The other characteristics and advantages of the invention will appear from the description hereinbelow, provided solely on an illustrative and non-limiting basis, to which are attached:  
         [0029]      FIG. 1  showing an internal combustion engine using the combustion control method according to the invention; and  
         [0030]      FIG. 2  is a diagram of the logic circuit used in the method according to the invention. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0031]      FIG. 1  illustrates schematically a direct-injection internal combustion engine of the Diesel type, which can operate in two modes: a traditional combustion mode, with injection of fuel around the combustion TDC and diffusion combustion, used at high loads, and a homogeneous combustion mode with a small crank angle injector, used at low and medium loads.  
         [0032]     This engine has at least one cylinder  12  with a combustion chamber  14  inside which combustion of an air-fuel mixture occurs. The cylinder has at least one direct fuel injection means  16 , comprising a fuel injector  18  supplied by a rail  20  (a system usually known as a “common rail”). This cylinder also has at least one air intake means  22  with an intake valve  24  and inlet pipe  26  and at least one burned-gas exhaust means  28  with a valve  30  and an exhaust pipe  32 . The inlet valve  24  and exhaust valve  30  are operated to open and close by any known means such as classical camshafts or camshafts that vary the lift phasing of these valves either together or independently of each other, such as those known as VVA (variable valve actuation) or VVT (variable valve timing).  
         [0033]     As can be seen from the figure, the exhaust pipes  32  of this engine are connected to an exhaust manifold  34  while the inlet pipes  26  are connected to an inlet manifold  36 . The exhaust manifold is connected to an exhaust line  38  which includes a turbocompressor  40  that admits intake air under pressure into inlet manifold  36  through a pipe  42  (only the beginning and the end of this pipe are shown in the figure for simplification). The exhaust line also has a bypass line  44  known as the EGR (exhaust gas recirculation) line, controlled by a valve  46  called the EGR valve, that recirculates some of the exhaust gases to the intake. The circuit thus formed, called the EGR circuit, can be of the high-pressure type as illustrated in  FIG. 1 , with the burned gases being picked up in the exhaust line upstream of turbine  40 a of turbocompressor  40  and possibly a counterbalance valve  102 , with the intake pressure being modulated by the valve  46 , possibly a cooling device  47 , and an outlet of these gases into the intake line upstream of manifold  36  and downstream of compressor  40  of this turbocompressor and possibly a cross-section restrictor such as a rotary butterfly valve  100  for modulating the intake pressure. This EGR circuit can also be of the low-pressure type with burned gas being picked up in the exhaust line  38  downstream of a particle filter (not shown) and upstream of a possible cross-section restrictor (such as a rotary butterfly valve  102 ), a valve dedicated to the low-pressure EGR circuit (similar to valve  46 ), possibly a cooling device similar to device  47  and an outlet of these gases upstream of the compressor and downstream of a valve, if any (not shown). It should be noted that the engine can receive both types of EGR circuits which can then be used simultaneously or alternatively depending on the operating point.  
         [0034]     The engine also has a processing and control unit  48  known as the “engine computer” whose role is to control the various parameters linked to engine operation according to the information supplied thereto.  
         [0035]     This engine computer  48  has in particular a controller known as the “combustion controller” which receives information on the torque demand created by the driver pressing on the accelerator pedal  50  through a line  52  and on the speed of this engine through a line  54 . As a function of all this information, the computer  48 , after processing as will be described at greater length in the specification below, sends control orders through control lines  58   a,    58   b,    58   c,  and  58   d  to the various actuators that act on the air loop of this engine such as the EGR valve  46 , the actuator of turbocompressor  40 , and/or any other actuator of the air or exhaust loop, particularly with the aid of butterfly or other valves such as the valve  100  disposed at the engine intake or the valve  102  as described above. “Air loop” is understood to be any engine element such as pipes, valves, turbocompressor, or others that admit and control a fluid such as air, supercharged air, and/or burned gases in the intake manifold and the cylinders. Control orders are also sent through control lines  60  to the fuel loop, particularly to the fuel injection means  16 , so that the various fuel injection parameters can be controlled, such as injection pressure, injection time, injection phasing, etc. Likewise, the fuel loop includes any element (valve, pump, poppet valve, injection train, pump injector, etc.) for introducing fuel into the engine combustion chambers.  
         [0036]      FIG. 2  illustrates a logic circuit representing the combustion controller built into the engine computer  48  and having two distinct control modules, a module  62  for controlling the air loop and a module  64  for controlling the fuel loop, as well as an acquisition/specification module  66  for acquiring basic control data (driver demand, engine speed, and possibly other parameters (P) such as engine temperature) and supervising the control modules.  
         [0037]     The acquisition/specification module  66  contains a torque-determining unit  68  to establish the desired torque (Torque_des) and a unit  70  for determining the desired IMEP (Indicated Mean Effective Pressure) (IMEP_des) from the torque determined by unit  68 . Information linked to the position of accelerator pedal  50  (Pedal_pos), the engine speed (Ne), and any other parameters (P) such as information linked to the brake pedal position is sent to unit  68  while information on the desired torque (Torque_des), engine speed (Ne), and any other parameters (P) such as engine temperature, engaged transmission ratio, etc. is sent to unit  70 .  
         [0038]     The air loop control module  62  has an air circuit treatment unit  72 . The desired IMEP (IMEP_des) coming from unit  70  and the engine speed (Ne) are translated at the inlet to unit  72  into a specified air mass (Mair_sp) and to a specified burned gas ratio (BGR_sp) with the aid of maps  74  and  76 . This unit also receives information on the intake air mass (Mair_aspirated) and the burned gas ratio admitted by the engine cylinder (BGR) as well as any other parameters (P) such as atmospheric pressure. The magnitudes for intake air mass (Mair_aspirated) and burned gas ratio admitted to the engine (BGR) can come from direct measurements or observers reconstituting these data from other measurements. After processing of all this information, this unit  72  sends control instructions to the various elements  78  controlling the engine actuators and which can influence the parameters relating to air and/or recirculated burned gases admitted into the engine cylinders in order to bring these parameters as close as possible to the specified values.  
         [0039]     The control module  64  of the fuel loop has an IMEP processing unit  80  for obtaining a specified IMEP (IMEP_sp) from the inputs on the intake air mass (Mair_aspirated), the desired IMEP (IMEP_des), and possibly other parameters (P) such as engine temperature, engine speed, and/or parameters linked to burned gas recirculation such as measured or estimated burned gas ratio (BGR). This module  64  also includes an injection correction,unit  82  defining the injection parameters (mass of fuel to be introduced into the combustion chamber for each injection (Mfuel_i), phasing of each injection (SOI_i), and injection pressure (Pfuel)) which will be sent to the elements  84  controlling the injection means  16 . The inputs to unit  82  are: the fuel mass of each injection (Mfuel_i_sp), the phasing of each injection (SOI_i_sp), the injection pressure (Pfuel_sp), the burned gas ratio gap (BGR_gap), the intake air mass gap (Mair_gap), and possibly other parameters (P) such as engine speed (Ne), specified IMEP (IMEP_sp), or engine temperature. The injection parameters (Mfuel_i_sp, SOI_i_sp, and Pfuel_sp) result from maps  86 ,  88 , and  90  that take into account the specified IMEP (IMEP_sp) and the engine speed (Ne). The burned gas ratio gap (BGR_gap) represents the difference between the burned gas ratio adapted to the specified IMEP (BGR_IMEP_sp) resulting from a map  92  (taking into account the specified IMEP (IMEP_sp) and the engine speed (Ne)) and the measured or estimated burned gas ratio (BGR). Likewise, the intake air mass gap (Mair_gap) represents the difference between the air mass adjusted to the specified IMEP (Mair_IMEP_sp) resulting from a map  94 , taking into account the specified IMEP (IMEP_sp) and the engine speed (Ne) and the intake air mass (Mair_aspirated).  
         [0040]     When the engine is in operation, unit  68  determines the desired torque (Torque_des) from various parameters such as engine speed (Ne), driver demand by accelerator pedal position (Pedal_pos), and possibly other parameters (P) such as information linked to the brake pedal position. This desired torque is then transmitted to unit  70  that determines the desired IMEP that integrates, in particular, the requirements relating to riding comfort, engine friction, and deceleration regulation—all evaluated from the engine speed (Ne), and possibly other parameters (P) such as engine temperature, engaged transmission ratio, etc., all of which combine to define the desired IMEP (IMEP_des). The information on this IMEP is sent to the input of maps  74  and  76  of the air loop control module  62  to establish the air mass specifications (Mair_sp) and the burned gas ratio specifications (BGR_sp) as a function of engine speed (Ne). These specifications as well as the information on intake air mass (Mair_aspirated) and/or burned gas ratio admitted by the engine cylinder (BGR) and possibly other parameters (P) such as atmospheric pressure are submitted to air loop processing unit  72  which will try to meet these specifications by adjusting the controls  78  of the various air loop actuators such as the intake butterfly valve  100 , EGR valve  46 , and the element controlling turbocompressor  40  (variable-geometry turbocompressor, for example). The air mass (Mair aspirated) and burned gas ratio (BGR) actually admitted into the engine cylinder can be measured by any means or determined by “observers.” An “observer” is any means for obtaining an evaluation of this air mass and/or this ratio from measurements coming from the engine such as the air flowrate at the inlet of intake manifold  36  or upstream of turbocompressor  40 , the intake air pressure, the temperature of this air, the exhaust richness measurement, the exhaust pressure, the positions of the actuators, etc. From these evaluations, unit  72  provides loop control by evaluating their deviations from the specified values Mair_sp and BGR_sp at all times.  
         [0041]     Despite this loop control, the air mass and burned gas ratio entering the cylinders can deviate from the specified values, particularly in the transitional operating phases between homogeneous combustion mode and traditional combustion mode or in load transients. Also, the maximum torque produced by the engine is limited by the amount of air available at the cylinder inlet and hence the richness of the air-fuel mixture cannot exceed a certain value without causing emission of pollutants such as smoke.  
         [0042]     To guarantee optimized combustion, the control module of the fuel loop  64  takes these elements into account when determining the commands to be sent to control unit  84  of the fuel injection means  16 , which has the feature of having a significantly shorter response time than that of the air loop.  
         [0043]     The processing unit  80  of this module has a decision algorithm which, from the desired IMEP (IMEP_des) coming from unit  70 , the intake air (Mair_aspirated) in cylinder  12 , and possibly other parameters (P) such as engine heat, and engine speed (Ne), etc., defines the specified IMEP value (IMEP_sp) that will be used together with the engine speed (Ne) to determine the specifications for the fuel to be injected into the cylinders. These two data are in fact used as inputs for maps  86 ,  88 , and  90  to define the various setpoints of the injection parameters such as mass of fuel introduced into the cylinders for each injection (Mfuel_i_sp), the timing of each injection (SOI_i_sp), and the injection pressure (Pfuel_Sp). The index “i” used in the injection parameters corresponds to the various injections occurring in each cylinder during the combustion cycle.  
         [0044]     Also, a burned gas ratio adjusted to the specified IMEP (BGR_IMEP_sp) is defined, which ratio is determined by a map  92  identical to map  76  of air loop control module  62 , whose inputs are the specified IMEP (IMEP_sp) and the engine speed (Ne). It is then possible to evaluate the gap (BGR_gap) between the burned gas ratio adjusted to the specified IMEP and the measured or estimated ratio (BGR), then to submit this gap to unit  82  which will correct some of the injection parameters defined above that it receives at the input to send final control instructions to injection control unit  84 .  
         [0045]     Likewise, an air mass adjusted to the specified IMEP (Mair_IMEP_sp) is determined by a map  94  whose inputs are the specified IMEP (IMEP_sp) and the engine speed (Ne). The gap (Mair_gap) between the air mass adjusted to the specified IMEP and the measured or estimated intake air mass (Mair_aspirated) is evaluated then submitted to unit  82  for any corrections of some injection parameters.  
         [0046]     Of course, the decision unit  82  can take into account other parameters (P) than the gaps (BGR_gap and Mair_gap) described above to establish corrections to be made to the injection parameters it receives at the input, such as engine speed (Ne), specified IMEP (IMEP_sp), or engine heat.  
         [0047]     It may be noted that the use of the desired IMEP in the air loop control module  62  allows the air and/or burned gas to converge as quickly as possible on the IMEP value demanded by the driver, while the fuel loop control module  64  uses the specified IMEP value (IMEP_sp) and allows the fuel settings to be adjusted to the air and/or burned gas actually admitted into the cylinder. Thus, because of the invention, the fuel loop will be used to attempt to remedy the inertia of the air loop response.  
         [0048]     The present invention is not confined to the embodiments described above but encompasses all variants.  
         [0049]     Thus, the invention need not be equipped with a supercharger such as a turbocompressor, in which case the air admitted into the cylinders will be at close to atmospheric pressure. Also, the fuel direct injection means  16  can have any other form carrying out the same functions as the common rail: pump injector or equivalent system.  
         [0050]     Note that such a control device can also be applied partially or totally to spark ignition engines provided with a direct fuel injection device into the chamber and a burned gas recirculation device. In this case, combustion is controlled jointly by the air and burned gases present in the cylinder, fuel injection, and ignition. Thus, to determine the ignition-linked parameters, one may use the same decision trees as those used for injection alone in the case of Diesel engines, such as the use of maps as a function of specified IMEP (IMEP)_sp) and engine speed (Ne) to determine the basic value of these parameters, which can then be corrected according to the gap (BGR_gap, Mair_gap) between the magnitude linked to the recirculated burned gases and/or the air mass introduced into the combustion chamber and the reference values of this magnitude (BRM_IMEP_sp, Mair_IMEP_sp) established from the specified IMEP (IMEP_sp).  
         [0051]     The present invention is of course applied in the context of Diesel engines and specifically in the case of the engine described in French patents. 2,818,324 and 2,818,325 by the assignee which are incorporated by reference into the present specification. More specifically, this type of engine includes at least one cylinder with a cylinder head, a piston sliding in this cylinder, gas intake and exhaust means, a combustion chamber delimited on one side by the upper face of the piston including a nipple pointing toward the cylinder head and disposed at the center of a concave bowl, and at least one injector to inject the fuel with a crank angle less than or equal to  
       2   ⁢           ⁢   Arctg   ⁢     CD     2   ⁢           ⁢   F           
 
 where CD is the cylinder diameter and F is the distance between the point of origin of the fuel jets coming from the injector and the position of the corresponding piston at a crank angle of 50° C. with respect to the top dead center. More specifically, this crank angle is chosen between 0° and 120°.