Patent Publication Number: US-6983737-B2

Title: Method, computer program and control and/or regulating device for operating an internal combustion engine

Description:
RELATED APPLICATIONS 
   This application is the national stage of international application PCT/DE 02/02724, filed Jul. 24, 2002, designating the United States and claiming priority from German patent application Nos. 101 59 389.9, filed Dec. 4, 2001, and 102 23 677.1, filed May 28, 2002, the entire contents of which are incorporated herein by reference. 

   FIELD OF THE INVENTION 
   The invention relates first to a method for operating an internal combustion engine in dependence upon operating characteristic variables, such as rpm of a crankshaft, temperature of the internal combustion engine and/or temperature of the intake air. In the method, a temperature of the inducted air in a region close to the combustion chamber or in the combustion chamber itself is obtained, at least in approximation, from a detected or modeled temperature of the inducted air in a region remote from the combustion chamber. 
   The precise knowledge of the fresh air mass, which is disposed in the combustion chamber, is basically important for the operation of an internal combustion engine. This is used for mixture precontrol. Especially shortly after the start, when a lambda probe, which is used for mixture control, is not yet operationally ready, a precise detection of the air charge is required. 
   This is possible by means of an air mass sensor or by means of an intake manifold pressure sensor. The intake manifold pressure is, however, a very indirect charge signal. With knowing only the intake manifold pressure, the charge of the combustion chamber with fresh air cannot yet be computed. The knowledge of the temperature of the fresh air, which is inducted into the combustion chamber (without considering the mixing with hot residual gas which is possibly present), is, inter alia, required. 
   BACKGROUND OF THE INVENTION 
   From U.S. Pat. No. 6,272,427, it is known that, for otherwise like ambient conditions, a higher temperature of the intake air causes, inter alia, the following: a higher tendency to knock; an improved vaporization of the fuel; a reduced wall film formation of the fuel on the inner walls of the intake manifold; and, a reduction of the inducted air mass and therefore a reduction of the needed fuel quantity. In the context of this background, modern controls for internal combustion engines process the intake air temperature which can be measured by a corresponding sensor or is computed via a corresponding temperature model. 
   Space reasons in the vicinity of the internal combustion engine are the cause that sensors, with which the temperature of the intake air can be measured, cannot be mounted in the immediate vicinity of the combustion chamber of the internal combustion engine; instead, these sensors are, for example, mounted in the air filter housing, in an air mass sensor, in a throttle flap support or in combination with a sensor for measuring the air pressure in the intake manifold. 
   In its path into the combustion chamber through the intake manifold, the intake air can become warm on the warm walls of the intake manifold and on other warm or hot parts which lie in the flow path. For this reason, this means that the temperature, which is measured with these sensors, is usually less than the actual temperature of the fresh air, which is enclosed in the combustion chamber after the end of the intake stroke and is not yet mixed with the hot residual gas which possibly is present in the combustion chamber. 
   For this reason, U.S. Pat. No. 6,272,427 suggests a correction of the measured temperature of the intake air. For this purpose, a weighting factor is used which is computed by means of characteristic lines or characteristic fields in dependence upon the intake air temperature, the engine temperature and an operating point of the internal combustion engine. 
   SUMMARY OF THE INVENTION 
   The present invention has the task of providing a method of the type mentioned initially herein which is so improved that it can be more easily programmed and supplies more precise results. 
   This task is solved with a method of the kind mentioned initially herein in that the determination of the temperature of the inducted air in the region near the combustion chamber or in the combustion chamber itself takes place under the assumption that the intake air has a modeled or detected initial temperature and that the intake air comes into thermal contact with a typical component during a contact time, which is typical for the type of internal combustion engine and for an operating state of the internal combustion engine, and the typical component has a modeled or detected temperature. 
   In the method according to the invention, the application of complex characteristic lines or complex characteristic fields is substantially unnecessary because the correction of the temperature of the inducted air takes place essentially on the basis of physical laws and mathematical formulations. These are considerably simpler to apply or to program than characteristic lines or characteristic fields. Furthermore, the consideration of the physical laws permits achieving a more precise computation result. 
   The method of the invention is based on several assumptions. 
   On the one hand, it is assumed in a simplifying manner that the warming of the inducted fresh air is affected by the contact with a typical component, which lies upstream of the combustion chamber, or at least a structural part of the internal combustion engine which lies upstream from the combustion chamber. This component or this structural part represents all warm components and structural parts of the internal combustion engine which lie in the flow path of the intake air. 
   Furthermore, it is assumed that the temperature increase of the fresh air takes place in advance of a possible mixing with hot residual gases in the intake manifold or in the combustion chamber. Furthermore, it is assumed that the heat quantity, which is transferred to the inducted fresh air (or, in rare cases, the heat quantity transferred from the inducted fresh air), is dependent upon the contact time, which is typical for a type of internal combustion engine, between the inducted fresh air and the structural part, which gives up the heat, or the structural parts which give up the heat. These assumptions correspond in the same way to the conditions in an RC-member in electrical engineering. There, the typical contact time would be realized by the “closed time” of an on/off switch. 
   On the basis of the assumptions in accordance with the invention, a differential equation of the first order results whose solution yields an exponential dependency of the temperature of the inducted air on the typical contact time. 
   The contact time, which is typical for an internal combustion engine type, can, in turn, be empirically determined in a simple manner. With the method of the invention, it is therefore possible to compute the warming of the fresh air inducted by an internal combustion engine based on the usual thermal equations without it being necessary to program complicated characteristic lines or characteristic fields. 
   First, it is suggested that the contact time, which is typical for a specific type of internal combustion engine, be obtained with the aid of test runs of the type of internal combustion engine at varying operating conditions, especially cold and warm internal combustion engines. Also, test runs with cold and warm intake air are possible. This is a procedure which has shown very good results in practice. In general, the typical contact time is inversely proportional to the rpm of the crankshaft. With the above test runs, the corresponding proportionality constant can be determined in a simple manner. Usually, the typical contact time would lie in the range of the duration of one intake stroke because the heat transfer is much greater for a flowing fluid than for a fluid at standstill. 
   In an advantageous configuration of the method of the invention, it is also suggested that the determination of the temperature of the inducted air takes place in the region near the combustion chamber or in the combustion chamber itself under the assumption that the heat quantity (which is exchanged between the inducted air and the typical component of the internal combustion engine with which the inducted air enters into thermal contact) is dependent upon a difference between the temperature, which is measured in a region remote from the combustion chamber, or the modeled temperature of the inducted air and the temperature of the typical components of the internal combustion engine with which the inducted air enters into thermal contact. 
   In this embodiment of the method of the invention, and in addition to the dependency of the exchanged heat quantity on the contact time, the dependency is also considered of the exchanged heat quantity on the temperature difference between the flowing fresh air and the at least one component. The precision for the determination of the warming of the inducted fresh air is again significantly improved in this way. 
   Preferably, the temperature of at least one inlet valve is used as the temperature of the component of the internal combustion engine. This is based on the thought that the inducted fresh air is heated on its path to the combustion chamber especially by the very hot inlet valve or its components. This assumption makes possible a very simple computation and nonetheless permits a high reliability of the determined temperature of the intake air. 
   Here, it is, in turn, preferred when the temperature of the inlet valve is obtained from a measured temperature of a coolant and/or of a cylinder head. The coolant temperature as well as the cylinder head temperature are determined in conventional internal combustion engines anyhow by means of sensors. Based on simple computation models, which consider the heat conductivity from the location of the temperature measurement to the inlet valve, the temperature of the inlet valve can be determined with great accuracy. In the simplest case, the temperature of the inlet valve can be set equal to the measured temperature without the temperature result being significantly falsified thereby. 
   In a four-stroke internal combustion engine, the temperature of the inducted air in the region near the combustion chamber or in the combustion chamber itself is preferably determined by the following formula: 
       Taevk   =     Taev   +       (     Tev   -   Taev     )     *     (     1   -     ⅇ       -     15   ⁢           [     sec   ⁢     /     ⁢   min     ]           nmot   ⁢           [     1   ⁢     /     ⁢   min     ]     *     tcontact   ⁢           [   sec   ]             )             
 
wherein:
 
   Taevk=corrected temperature of the intake air; 
   Taev=detected or modeled temperature of the inducted air in a region remote from the combustion chamber; 
   Tev=detected or modeled temperature of a component of the internal combustion engine; 
   nmot=detected rpm of the crankshaft of the engine; 
   tcontact=typical contact time wherein the inducted air warms by (1−1/e)*(Tev−Taev). 
   The typical contact time is a time constant wherein the inflowing gas is warmed by a specific amount of the difference temperature between the gas and the component. As the decisive variable in the exponent of the e-function, there remains only the rpm of the crankshaft of the internal combustion engine. With this simple formula, which is therefore also easy to program, the corrected temperature of the intake air can be determined with a high precision. Only the conditions at which the typical contact time is applicable must be determined, for example, by an experiment. 
   It is also possible that, in a four-stroke internal combustion engine, the determination of the temperature of the inducted air in the region near the combustion chamber or in the combustion chamber itself is determined in accordance with the following formula: 
       Taevk   =     Taev   +       (     Tev   -   Taev     )     *     (     1   -     ⅇ       -     NMOTWK   ⁢           [     1   ⁢     /     ⁢   min     ]         nmot   ⁢           [     1   ⁢     /     ⁢   min     ]           )             
 
wherein:
 
   Taevk=corrected temperature of the intake air; 
   Taev=detected or modeled temperature of the inducted air in a region remote from the combustion chamber; 
   Tev=detected or modeled temperature of a component of the internal combustion engine; 
   nmot=detected rpm of the crankshaft of the internal combustion engine; 
   NMOTWK=typical rpm of the crankshaft of the internal combustion engine at which the inducted air warms by (1−1/e)*(Tev−Taev). 
   In the same way as the above formula, it also applies here that this formula supplies precise results and is easy to program. The use of a typical rpm permits a still simpler computation. The formula can likewise be determined by test runs. For example, two curves can be determined which describe the dependency of the inducted fresh air mass on the pressure in the intake manifold at a typical rpm and different temperatures of the inducted air. The equation is made usable for a typical rpm. 
   That embodiment of the method of the invention is especially advantageous wherein the temperature of the inducted air in the region near the combustion chamber or in the combustion chamber itself is used for determining the fresh air charge disposed in the combustion chamber at the end of an induction stroke. The fresh air charge is, in turn, used in order to precontrol the fuel quantity to be injected into the combustion chamber. Finally, the method of the invention makes possible that the air/fuel mixture present in the combustion chamber can be adjusted very precisely in the desired manner. 
   For this purpose, it is provided in accordance with the invention that the charge of the combustion chamber is determined based on the following equation: 
       rffg   =     FUPSRLROH   *       273   ⁢           ⁢   K     Taevk     *     (     ps   -       rfrg   *   Trgk       FUPSRLROH   *   273   ⁢           ⁢   K         )           
 
wherein:
 
   rffg=freshly inducted air charge; 
   FUPSRLROH=variable dependent upon operating point; 
   rfrg=normalized residual gas charge referred to the piston displacement; 
   Taevk=corrected temperature of the inducted air; 
   ps=pressure in the intake manifold; 
   Trgk=temperature of the residual gas in (K) expanded to the intake manifold pressure but assumed idealistically unmixed. 
   The above-mentioned equation is also characterized as the equation of the adiabatic charge exchange model. The factor FUPSRLROH is an operating point dependent variable but independent from the intake manifold pressure and the temperature and this variable describes the slope of the characteristic line rl=f(ps) at constant rfrg and Trg (dependency of the inducted fresh air mass on the pressure in the intake manifold). The equation considers all effects of the charge exchange. Here, the influence of the heat transfer from components of the internal combustion engine to the fresh air are considered only with the aid of the variable Taevk. Based on the intake pressure, which is usually detected by a pressure sensor in the intake manifold, the fresh air charge can be determined with high precision without an air mass sensor being necessary. 
   The invention relates also to a computer program which is suitable for carrying out the method when the computer program is run on a computer. It is preferred when the computer program is stored in a memory, especially in a flash memory. 
   The subject matter of the present invention is also a control apparatus (open loop and/or closed loop) for operating an internal combustion engine. Here, it is preferred when the apparatus includes a memory on which a computer program of the above type is stored. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The invention will now be explained with reference to the drawings wherein: 
       FIG. 1  is a schematic illustration of an internal combustion engine with some of its components; 
       FIG. 2  is a flowchart which describes a method for correcting an intake air temperature of the internal combustion engine of  FIG. 1 ; 
       FIG. 3  is a diagram of a function which is used in the method for correcting the intake air temperature in  FIG. 2 ; and, 
       FIG. 4  is a function diagram which shows a method for computing a fresh air charge by means of a corrected intake air temperature. 
   

   DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION 
   In  FIG. 1 , an internal combustion engine has the reference numeral  10 . The engine includes several cylinders of which only that having reference numeral  12  can be seen in FIG.  1 . In the cylinder, a piston  14  is slidingly guided which delimits a combustion chamber  16  The piston  14  is connected to a crankshaft  18  via a connecting rod (no reference numeral). The crankshaft  18  is only shown symbolically. 
   Fresh air is supplied to the combustion chamber  16  via an intake manifold  20  and an inlet valve  22 . In the intake manifold  20 , an injection nozzle  24  is provided which is connected to a fuel system  26 . In the intake manifold  20 , a throttle flap  28  is mounted upstream of the injection nozzle  24 . The throttle flap  28  can be moved into a desired position by an actuating motor  30 . The temperature of the supplied fresh air is detected by a sensor  32  and the pressure of the supplied fresh air is detected by a sensor  34  upstream of the throttle flap  28 . 
   The hot exhaust gases are conducted away from the combustion chamber  16  via an outlet valve  36  and an exhaust-gas pipe  38 . A catalytic converter  40  purifies the exhaust gases. Between the outlet valve  36  and the catalytic converter  40 , the temperature of the exhaust gas is detected by a temperature sensor  42  and the pressure of the exhaust gas is detected by a pressure sensor  44 . 
   The internal combustion engine  10  has a double continuous camshaft control. This means that the closing time points and opening time points of the inlet valve  22  and the outlet valve  36  can be adjusted continuously. For this purpose, the inlet valve  22  is actuated by an inlet camshaft  46  and the outlet valve  36  is actuated by an outlet camshaft  48 . The camshafts  46  and  48  are so adjusted during operation by actuators  50  and  52  that the desired closing time points or opening time points are present. 
   The air/fuel mixture, which is present in the combustion chamber  16  of the internal combustion engine  10 , is ignited by a spark plug  54  which, in turn, is driven by an ignition system  56 . 
   The operation of the internal combustion engine  10  is controlled (open loop and/or closed loop) by a control apparatus (open loop and/or closed loop)  58 . The control apparatus  58  is connected at the input end to the temperature sensor  32  and the pressure sensor  34  in the intake manifold  20 . In addition, the control apparatus receives signals from the temperature sensor  42  and the pressure sensor  44  in the exhaust-gas pipe  38 . A transducer  60  supplies signals from which the rpm of the crankshaft  18  and its angular position can be obtained. 
   In the same manner, sensors  62  and  64  are provided which detect the angular position of the inlet camshaft  46  or the outlet camshaft  48 . At the output end, the control apparatus  58  is connected to the following: the injection nozzle  24 ; the actuating motor  30  of the throttle flap  28 ; the actuators  50  and  52  of the inlet camshaft  46  and of the outlet camshaft  48 , respectively; and, to the ignition system  56 . A temperature sensor  66  detects the temperature of a cylinder head (not shown) of the internal combustion engine  10 . 
   In order to be able to determine that fuel quantity which corresponds to the torque wanted by the operator of the internal combustion engine  10  and for which the wanted mixture composition in the combustion chamber  16  is obtained, it is necessary to determine the quantity of the fresh air arriving in the combustion chamber  16  in a work cycle. 
   For this purpose, a sensor could also be utilized; however, the sensor is not used because of cost reasons when, as here, a pressure sensor  34  is present in the intake manifold  20 . In an embodiment not shown, an air mass sensor is installed in the intake manifold in lieu of the pressure sensor. In this case, the pressure in the intake manifold would have to be determined for determining the air charge of the combustion chamber from the detected signals. 
   As shown in  FIG. 2 , the signal of the temperature sensor  66  is fed into a processing block  68 . In block  68 , based on a numerical model, the temperature Tev of the inlet valve  22  is determined from the temperature Tmot of the cylinder head. With such a model, a temperature of the intake manifold  20  could also be easily overall determined with this temperature being typical for the present computation. The inlet valve  22  is a typical component insofar as it represents, for the present type of internal combustion engines ( 10 ), the warm components of the internal combustion engine  10  which are typical for the warming of the intake air. 
   From a temperature Tans of the inducted air, which is detected by the sensor  32 , a temperature Taev is determined based on a numerical model in a processing block (not shown). Here, the temperature Taev is that temperature which the inflowing air exhibits in a region lying upstream of the inlet valve  22  and which region is insofar remote from the combustion chamber. However, in most operating states of the internal combustion engine  10 , the temperature Taev is higher than Tans because the inflowing air is already somewhat warmed by the contact with the components disposed in the intake manifold. It is, however, assumed in the modeling that a warming of the inflowing gas does not take place because of possibly backflowing gas. At  70 , the difference between the temperature Tev of the inlet valve  22  and the temperature Taev of the inducted air is formed. 
   The value nmot of the rpm of the crankshaft  18 , which is made available by the sensor  60 , is compared in  72  to the value 1 and the value which is higher is outputted. The output of block  72  is used as a divider in a division block  74 . Because of the comparison in  72 , it is prevented that the divider assumes the value 0. 
   A constant NMOTW is fed into the division block  74  as the quantity which is to be divided. This constant is an applicable rpm value which describes the intensity of the heat contact of the inducted fresh air with the inlet valve  22 . Here, NMOTW is a typical engine rpm for which the inducted air warms by the amount 1/e (Tev−Taev)  when flowing into the combustion chamber  16 . NMOTW corresponds to a normalized contact time which is typical for a specific type of internal combustion engine and a specific operating state. This contact time will be discussed in detail hereinafter. The contact time is determined empirically. At higher rpms, the temperature adaptation is less. 
   The output of the division block  74  is fed into a characteristic line EXPSLP which is identified in  FIG. 2  by reference numeral  76 . This characteristic line is also shown in FIG.  3 . The following function is reflected in this characteristic line: 
       x   =     1   -     ⅇ     -     NMOTWK   nmot               
 
   The output of the characteristic line EXPSLP in block  76  is fed into a multiplier  78  and the difference, which is formed in  70 , is fed into the multiplier  78 . This difference is between the temperature Tev of the inlet valve  22  and the temperature Taev of the intake air. The output of the block  78  is added in  80  to the temperature Taev of the intake air and the result is outputted as the corrected intake air Taevk. 
   The corrected temperature Taevk is, to a very close approximation, the temperature of the fresh air enclosed at the end of the intake stroke in the combustion chamber  16  of the internal combustion engine  10  (that is, in the closest possible region to the combustion chamber). The sequence shown in  FIG. 2  corresponds to a processing of the formula: 
       Taevk   =     Taev   +       (     Tev   -   Taev     )     *     (     1   -     ⅇ       -     NMOTWK   ⁢           [     1   ⁢     /     ⁢   min     ]         nmot   ⁢           [     1   ⁢     /     ⁢   min     ]           )             
 
   This formula considers that the determination of the fresh air present in the combustion chamber takes place after the end of the intake stroke while utilizing a so-called “typical contact time”. This contact time is determined for a specific type of internal combustion engine and a specific operating state by experiments, for example, test runs of the internal combustion engine in the cold and warm states. Often, this contact time corresponds approximately to that time span during which the inducted fresh air flows past at the hot inlet valve  22  before it reaches the combustion chamber  16  itself. In the present embodiment, the contact time is approximately equal to the duration of one intake stroke. The typical rpm NMOTWK is determined from the typical contact time via a normalization with the rpm for which the typical contact time was determined. 
   In addition, for the determination of the temperature of the fresh air present in the combustion chamber  16  at the end of the intake stroke, the difference is also considered between the temperature of the inducted air, which is measured by the temperature sensor  32 , and the temperature Tev of the injection valve  22 , which is modeled from the temperature Tmot of the cylinder head of the internal combustion engine  10 . 
   As shown in  FIG. 4 , the temperature Taevk of the fresh air, which is enclosed in the combustion chamber  16  at the end of the intake stroke, is used for the determination of a relative charge of the combustion chamber  16  with fresh air. The temperature Taevk is determined in the manner described above. In the formula given in  FIG. 4 , this fresh air charge is identified by rffg. Here, rffg=100% when the piston displacement of the combustion chamber  16  is filled with fresh air at a pressure of 1013.25 hPa and 273.15 K. 
   The signals, which are detected by the sensors  32 ,  34 ,  60 ,  42 ,  44 ,  62  and  64 , are inserted directly or indirectly into the formula given in FIG.  4 . These signals are: Taev (temperature of the inducted fresh air), ps (pressure in the intake manifold), nmot (rpm of the crankshaft  18 ), Tabg (exhaust gas temperature), pabg (pressure of the exhaust gas in the exhaust-gas pipe  38 ) and wx (specific angular positions of the crankshaft  18  as well as the inlet camshaft  46  and the outlet camshaft  48 ). The corrected temperature of the fresh air present in the combustion chamber is determined from the temperature Taev of the inducted fresh air in a block  82  in accordance with the diagram of FIG.  2 . 
   The formula, which is presented in  FIG. 4 , considers also, as needed, residual gas present at the end of the intake stroke in the combustion chamber  16  Such a residual gas is present in the combustion chamber  16  when the internal combustion engine  10  has an internal or external exhaust-gas recirculation. In the formula presented in  FIG. 4 , the residual gas is considered by the variable rfrg which is the relative charge of the combustion chamber  16  with residual gas. Here, rfrg=100% when the piston displacement of the combustion chamber  16  is filled with residual gas at a pressure of 1013.25 hPA and a temperature of 273.15 K. 
   The variable Trgk is the mean temperature of the total residual gas under the assumption that it is expanded (unthinned with fresh air) to the pressure ps present in the intake manifold  20 . The factor FUPSRLROH is an operating point dependent quantity independent, however, from the pressure ps in the intake manifold  20  and from the temperature Taev of the inducted fresh air. For constant rfrg (relative charge of residual gas) and Trg (mean temperature residual gas), FUPSRLROH describes the slope of a characteristic line which couples the relative charge of the combustion chamber  16  with the fresh air to the pressure ps in the intake manifold  20 .