Process and apparatus for controlling the combustion course in an Otto combustion engine

The invention provides a process and apparatus for controlling combustion in an Otto combustion engine in which the control variables that control combustion are determined for a particular power cycle as a function of the detected combustion course of a preceding power cycle. According to the invention, a desired burn-through function value for a particular power cycle is precalculated based on values of pertaining influence factors detected in a preceding power cycle, to determine an actual burn-through function value of the particular power cycle in real time. The desired burn-through function is compared with the actual burn-through function and actualized values for the burn-through function influence factors are determined. These factors are used to determine the control variable values for a subsequent power cycle.

BACKGROUND AND SUMMARY OF THE INVENTION 
This invention relates to a process and apparatus for controlling the 
combustion in an Otto combustion engine. In conventional engine combustion 
controls, it is known to make a preliminary determination of engine 
control variables, such as the ignition point, the injection start, the 
injection end and the throttle valve angle, by accessing a plurality of 
characteristic curves and characteristic diagrams. By detecting certain 
engine operating parameters, such as the intake air mass, engine 
temperature, rotational speed etc, these engine control variables are 
calculated during the charge cycle phase. With the exception of the known 
knock control and lambda control, no alignment takes place with the actual 
combustion course which does not start before the high-pressure cycle. 
Thus, during lambda control, it is not the combustion course, but rather 
the exhaust gas, which is analyzed. 
More specifically, to control combustion in Otto engines, it is known to 
determine engine control variable values for a subsequent power cycle by 
means of a control device, as a function of the combustion course of a 
preceding power cycle, using measured actual condition variables to access 
stored characteristic diagrams. Conventionally, in this case, the detected 
instantaneous values of one or several measurable variables representative 
of the course of the combustion are used directly as feedback values which 
are compared in the control unit with desired values determined from 
stored characteristic diagrams. From the control deviation determined in 
this manner, the control elements for the next power cycle are controlled 
so as to reduce the control deviation. Thus, for example, German Patent 
Document DE 31 28 245 A1, discloses a process for controlling combustion 
in internal-combustion engines in which the course of the combustion 
chamber pressure is detected and is compared with a stored characteristic 
curve. Determined deviations are then controlled by adjusting the mixture 
formation and/or the ignition system of the internal-combustion engine. 
For cylinder-specific engine control, it is known to store individual 
characteristic diagrams for the individual cylinders; see German Patent 
Document DE 42 28 053 A1. 
A control device for an internal-combustion engine disclosed in U.S. Pat. 
No. 5,200,898, includes a neuronal network to which information is 
periodically fed concerning the actual throttle valve angle and its rate 
of change. The neuronal network performs a preliminary calculation of the 
throttle valve opening angle, which is used by the control device, among 
other things, for the control of a fuel injection unit. 
In an ignition system for an internal-combustion engine disclosed in 
European Patent Document EP 0 114 490 A2, a parameter representative of 
the fuel load of the operating space is measured before ignition is 
triggered in order to estimate the combustion characteristics for the 
current power cycle and a suitable ignition point, to reduce fluctuations 
in the generated engine torque from one power cycle to the next. 
Japanese Patent Document JP 5-163996 (A) discloses an engine control in 
which the engine torque is controlled to a desired value by adjustment of 
the air intake quantity and the ignition point. 
U.S. Pat. No. 4,987,888 discloses a combustion control in which 
combustion-relevant actual-condition variables are detected and, as a 
function thereof, the operating conditions (for example, air intake 
quantity) in a later power cycle are estimated. The estimated operating 
conditions are used to determine the combustion-relevant control variable 
values. 
The object of the invention is to provide a process and apparatus by means 
of which a comparatively precise control of the combustion course in an 
Otto combustion engine is achieved, taking into account the thermodynamics 
of the combustion operation as extensively as possible. 
This object is achieved by the process and apparatus according to the 
invention, in which the control variable values for a subsequent power 
cycle are determined based on actualized values of factors which influence 
the so-called "burn-through function" (the integral of the combustion 
course curve with respect to time, or with respect to the crank angle). 
The actualized influence factor values are obtained by comparing a desired 
time precalculated during the charge cycle phase of a power cycle with an 
actual burn-through function evaluated in real-time during the 
high-pressure phase of a power cycle. The desired burn-through function 
value for a particular power cycle is precalculated in this case based on 
detected or derived values of the burn-through function influence factors, 
which are representative of the actual engine condition of a preceding 
power cycle. In the case of an engine with several cylinders, this 
preferably takes place separately for each individual cylinder. 
Since the burn-through function reflects the thermodynamics of the 
combustion operation more precisely than do individual measurable 
variables, in comparison to engine controls which are based only on the 
observation of individual ones of such measurable variables, much more 
precise control of the combustion course is achieved. Control variables 
for the next power cycle which are to be influenced may be, for example, 
the start of injection, the end of injection, the ignition points and the 
throttle valve angle. To determine the actual engine operating condition, 
engine parameters such as air mass, temperature and rotational speed can 
be used, as well as additional measured variables such as the residual 
exhaust gas content and the lambda value. In this manner, actual fuel 
conversion into thermal energy is observed, and can be controlled taking 
into account the given marginal conditions, such as the driver's intent 
and operating requirements. 
By means of the process according to the invention, cyclical fluctuation in 
the instantaneous power point can be evaluated and worked into the control 
strategy. In particular, the transition behavior of the engine control in 
transient operation is improved significantly in comparison to 
conventional controls. In addition, in this type of combustion control, 
the large number of characteristic curves and characteristic diagrams 
which are otherwise required for conventional engine controls, will no 
longer be necessary. 
Individual control of the cylinders permits optimization of each individual 
cylinder while taking into account the cylinder synchronization. Because 
of the real-time evaluation of the actual burn-through function, a 
separate knock sensor is not required. Series divergences, manufacturing 
tolerances, ignition and firing differences, aging phenomena as well as 
effects of combustion chamber deposits may be taken into account in the 
control itself without the requirement of safety supplements, such as 
retarding an ignition point. 
In a further embodiment of the invention, a characteristic-diagram-based 
determination of the position of the combustion center is used by means of 
the actual engine condition and the actual burn-through function and for 
the steady-state engine control. For this purpose, the control device 
which carries out the process may have a corresponding unit for 
determining the position of the combustion center. 
In another embodiment of the invention, a transient control is superimposed 
on the steady-state control. For such transient control, in addition to 
the steady-state controller output signal, the information concerning the 
instantaneous operating point and/or the instantaneous engine power or the 
engine consumption are taken into account. 
In yet another embodiment of the invention, the actual burn-through 
function is evaluated without difficulty in real time, by means of a 
neuronal network. For this purpose, the generalizing and learning capacity 
of the network as well as its self-organization function can be utilized 
for the independent establishment of a relationship between an input 
signal to be classified and an intended output signal. The use of such 
artificial intelligence eliminates the need to solve the thermodynamic 
equations characteristic of the burn-through function in a 
high-expenditures manner by means of a computer in real time, as well as 
the need to iterate them by way of the crank angle. 
Other objects, advantages and novel features of the present invention will 
become apparent from the following detailed description of the invention 
when considered in conjunction with the accompanying drawings.

DETAILED DESCRIPTION OF THE DRAWINGS 
The control device illustrated in the Figure monitors the actual condition 
of the combustion course of the engine 1 to be controlled. For this 
purpose, the actual-condition detecting unit 2 detects measured variables 
relevant to the combustion operation and calculates the remaining relevant 
engine parameters, particularly the engine rotational speed, the starting 
temperature and pressure of a power cycle, as well as the residual exhaust 
gas content and the lambda value. Using these detected quantities, a 
calculating unit 3 precalculates the desired burn-through function in the 
charge cycle phase of the respective power cycle. 
As is known, the burn-through function is defined as an integral of the 
combustion course with respect either to time or the crank angle. To 
precalculate the burn-through function, influence factor equations are 
used, which describe the separate influences of the individual operating 
parameters on the action of the engine. Therefore, in order to determine 
how the burn-through function reacts to changes of the operating 
parameters, the engine type is indexed beforehand at suitable operating 
points, and systematic series of measurements are carried out until the 
influence factor equations are determined with sufficient certainty. The 
precalculation is based on suitable reference points, of which several are 
provided, along the complete operating range. 
In parallel to the precalculation of the desired burn-through function 
value in the unit 3, a neuronal network 4 receives as inputs, one or 
several detected quantities which are representative of the combustion 
course, such as the course of the combustion chamber pressure as a 
function of the crank angle and/or the lambda value and the exhaust gas 
temperature. Based on these inputs, the neuronal network 4 evaluates the 
actual burn-through function in real time, during the high-pressure phase 
of the respective power cycle. Use of artificial intelligence permits 
ready determination of the actual burn-through function in real time, 
eliminating the need for a highly calculation-intensive solution of the 
underlying thermodynamic equations, and an iteration by way of the crank 
angle. It is known that the determined burn-through function value can be 
used to derive the quantities relevant to such as combustion duration, 
apparent ignition lag, residual exhaust gas content and internal medium 
pressure. In addition, simultaneous knock detection is possible, which 
makes a separate knock sensor unnecessary. 
The data of the precalculated desired burn-through function from the 
calculating unit 3, and of the determined actual burn-through function 
from the neuronal network 4 are supplied to a subsequent comparison unit 
5, which carries out a desired-value actual-value comparison of the 
burn-through functions. By reversing the functional relationship used for 
precalculation of the burn-through function, the comparison unit 5 
determines the actual values of the influence factors which determine the 
burn-through function (such as the ignition point, the lambda value, the 
starting temperature and pressure, the residual exhaust gas content and 
the rotational speed) as a function of the relevant burn-through function 
parameters (such as the combustion duration, the apparent ignition lag and 
form parameters), that is, the slope adaptation of the burn-through 
function curve, in such a manner that these actual values fit the actual 
real time burn-through function determined by the neuronal network 4. 
This information concerning the optimal instantaneous influence factor 
values is output from the comparison unit 5 to a steady-state control unit 
6, which provides optimal control variables (the ignition point (ZZP), the 
injection start (ti), the injection end (ta) and the throttle valve angle 
(DK)), using the apparent ignition lag as well as the combustion center 
position as control criteria to determine the ignition point, and using 
the apparent ignition lag, the combustion duration, and the form parameter 
of the burn-through function as control criteria for the lambda value. 
Information concerning the combustion center position is supplied to the 
steady-state control 6 by a unit 11 which accesses a characteristic 
diagram stored therein, based on the actual burn-through function which it 
receives from the neuronal network 4 and the actual measured variables and 
engine parameters for the actual-condition detecting unit 2, to determine 
the combustion center position. 
The output signal of the steady-state control 6 is fed to a transient 
control 9 which may comprise a fuzzy logic control unit or a conventional 
PI(D) control unit. Additional input information provided to the transient 
control 9 consists of the actual power and actual consumption in the 
particular power cycle, as determined by a unit 7 which receives input 
information concerning the actual burn-through determination from the 
neuronal network 4, and the actual engine condition data from the actual 
condition detecting unit 2. By means of the same input information, a unit 
8 which is arranged in parallel to the unit 7 queries a characteristic 
operating point diagram stored therein, to determine weighting factors for 
the type of engine control desired by the driver; that is, for the 
operating point with respect to the power, the consumption and the 
emission. In this case, the driver's requirement is detected by reference 
to the throttle valve change, and by observation of past power cycles and 
the possible prediction of the future power cycle. By including this 
information, the transient control unit 9, may correct the output signal 
of the steady-state control as required by taking into account the 
driver's intention and the respective operating point requirements, the 
whole above-described control event taking place individually while taking 
into account the cylinder synchronization for each cylinder. In an 
output-side unit 10, the output signal of the transient control unit 9 is 
converted into corresponding engine control variable values, which are 
provided to the engine 1 for a subsequent power cycle. 
The described control concept permits a controlled multivariable control in 
which operating point changes are assigned to a corresponding control 
variable change. The actual fuel conversion into thermal energy is tracked 
and is controlled based on the given marginal conditions, such as the 
driver's intention and the operating point requirements, thereby 
implementing an optimal control variable adaptation. By the use of a 
neuronal network to determine the actual burn-through function and/or a 
fuzzy control unit as a transient control, the real-time application of 
this control is facilitated. An operating point change in response to a 
driver's input is thus readily adapted to the requirements for desired 
power, consumption, emission, smooth running and noise. Control variables 
are optimized individually for each cylinder by a thermodynamic analysis 
and evaluation of the actual burn-through function obtained from a 
combustion-course-determining quantity, such as the combustion chamber 
pressure course, by means of the neuronal network and the precalculated 
desired burn-through function. 
It is understood that the control units individually illustrated in the 
figure do not have to be separate components. Rather, they are to be 
considered individual functional units for illustrating the control 
sequence which, in a suitable manner, are combined to form respective 
control components. 
Although the invention has been described and illustrated in detail, it is 
to be clearly understood that the same is by way of illustration and 
example, and is not to be taken by way of limitation. The spirit and scope 
of the present invention are to be limited only by the terms of the 
appended claims.