Method of regulating or controlling internal combustion engine during cyclic working process

The invention relates to a method for regulating or controlling an internal combustion engine operating in a cycle process with internal combustion using a calculation model in which the cycle process or sections of the cycle process of the internal combustion engine is subdivided or divided into individual sub-processes. and the operating state within each sub-process is determined on the basis of measured values, stored and / or applied data in order to determine control variables for the operation of the internal combustion engine.

Innovations such as turbochargers, exhaust gas recirculation, multiple injection and / or partially / fully variable valve controls introduced in recent years in internal combustion engines have significantly increased the number of manipulated variables available for regulation. The possibilities resulting from the combination of the manipulated variables are generally very complex and cannot be adequately captured using conventional global approaches such as mean value models or map-based models.

The high demands placed on modern internal combustion engines with regard to consumption, emissions and driving characteristics require control concepts that cannot be implemented without recording the current engine status. Since many of the variables required for regulation cannot be measured or can only be measured by using expensive sensors (that is, sensors that are unsuitable for series production), the use of new types of calculation models is imperative.

The computing capacities within the engine control are severely limited, which results in high demands on the real-time capability of such computation models.

Currently available methods for calculating the operating state of an internal combustion engine do not meet the requirements of modern control concepts or only meet them unsatisfactorily. The approaches used can be divided into three groups:

Numerical methods are based on a numerical integration of the relationships characteristic of the cycle over the duration of the cycle (e.g. four cycles = 720 ° crank angle). Due to the high computing effort, such methods are not real-time capable under the conditions prevailing in series use.

Cylinder pressure-based methods use that measured by a suitable sensor and with suitable thermodynamic methods

AT 006 293 Ul evaluated cylinder pressure curve for the calculation of the current engine operating state. The sensors available for such methods are, however, too expensive for series use or only suitable for use on the test bench.

Further known methods are based on assumptions and / or restrictions that are based on a specific configuration of the internal combustion engine. Such models only aim at partial functions and cannot be generalized.

The object of the invention is to develop a method with which the operating state of an internal combustion engine can be determined very simply and quickly, but nevertheless with sufficient accuracy, in order to be able to obtain control variables that are used for regulation or control even with electronic control units (ECU) available in series operation . Control of the internal combustion engine are suitable,

According to the invention, this is achieved in that the calculation models for the individual sub-processes are based on at least partially different assumptions and / or have different simplifications and that the time limits of the sub-processes are calculated at least partially as a function of at least one variable engine operating parameter. The at least one variable engine operating parameter is measured or - depending on the engine operating state - is predetermined, for example, by the electronic control unit (ECU).

It is essential to the invention that the intervals within which the individual calculations are carried out are not simply reduced. The limits of the sub-processes are not rigidly tied to predetermined crank angles, but are made dependent on predetermined engine operating parameters. The advantage that can be achieved in this way is that map-controlled internal combustion engines with variable valve trains, variable injection times and the like. can be mapped in a suitable manner. Suitable simplifications can be made within the individual sub-processes, which allow a completely analytical mapping, but the simplifications, due to their precise adaptation to this sub-area of ​​the work cycle, do not cause a disruptive deterioration in the mapping quality. It is decisive that the operating conditions do not essentially change within a sub-process.

For example, if a sub-process describes a portion of the intake stroke that begins with the intake valve fully opened and ends at a point where the intake valve is fully closed, then for

AT 006 293 U1 uses the entire sub-process as a simplification of the mean value for the inlet cross-section, which makes it easier to model the gas movement. Furthermore, to simplify the process, the piston speed is assumed to be approximately constant for each sub-process. The error resulting from this assumption will later be compensated retrospectively.

The sub-processes can be defined by the fully open state of the inlet and / or outlet valves, by the combustion process, by the direction of movement of the piston, by the compression process and / or by the expansion process. The limits of the sub-processes can be determined by the position of the inlet and / or outlet valves, as well as by the beginning and the end of the combustion process or processes.

The calculation of the solution, which can be carried out at any crank angle, is carried out in sections, beginning with an initial state defined at any section change in the cycle, with the operating state being calculated at the end of a section in a calculation step. In the same way, however, the operating state can also be determined for each crankshaft angle lying inside the section. In this way, a time profile of the operating state can also be recorded.

Since the relationships described by comparison processes have already been established analytically, in particular algebraically, it is possible for the operating status of each sub-process to be recorded in real time.

In this way, it is provided in a further embodiment of the invention that the operating state at the end of the previous sub-process is assigned to the initial conditions of the next sub-process.

At least one variable from the group of torque, mass flow, load state of the cylinder, energy of the exhaust gases and heat flow of the cylinders is assigned to the operating state.

Depending on the operating state to be recorded, at least one engine operating parameter from the group of inlet pressure, inlet temperature, composition of the gas in the intake manifold, exhaust gas pressure, exhaust gas temperature, composition of the exhaust gas in the exhaust manifold, parameters of the valve train, parameters of the combustion and general engine operating parameters such as speed and wall temperature can be determined will. However, not all engine operating parameters have to be measured, since results from algorithms can also be used in some cases. To improve the accuracy of the calculation method, it can be provided that at least one engine be4

AT 006 293 Ul drive parameters is determined analytically and metrologically and that calculated values ​​are compared in a manner known per se, with preferably at least one engine parameter from the group of mass flow, cylinder pressure, air-fuel ratio and torque being determined analytically and metrologically.

In order to simplify the calculation process, it is advantageously provided that the effective flow cross-sections of the valves are approximated by rectangular or step-shaped curves.

Due to the flexible subdivision of the cycle, the calculation method is not tied to the type of valve train (rigid, partially / fully variable; number of inlet and outlet valves). Different combustion processes (auto or external ignition; number of partial burns) only differ in the analytical solution of the sections describing the combustion. The calculation works independently of the configuration of the internal combustion engine and is not impaired either by the use of pressure stages (compressor, turbines, etc.) or by devices for internal or external exhaust gas recirculation.

The method thus includes a methodology with the help of which it is possible to calculate states for which conventional methods require a numerical integration without performing this integration. The processes taking place during gas exchange or combustion are generally characterized by variables that can be changed over time (e.g. valve lift, combustion process, ...). These temporal values ​​are represented by simplified processes (e.g. Rectangular curves), which makes it possible to define sub-processes that can be clearly separated from one another. The interval limits are flexible, but known a priori through the definition of the intervals. The sub-processes are no longer dependent on the time course of the control variables, i.e. on the charge exchange and the combustion course, and can be analyzed analytically.

The invention is explained in more detail below with reference to the figures.

1 shows a schematic representation of an internal combustion engine for carrying out the method according to the invention, FIG. 2 shows a first exemplary embodiment of the method according to the invention, FIG. 3 shows a second exemplary embodiment of the method according to the invention, and FIG. 4 shows a valve lift diagram.

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Example: filling model for variable valve train

The following assumptions and simplifications are made:

Consideration of the intake stroke; The gas condition at the outlet is the initial condition (alternatively also with an exhaust stroke)

Calculation of the load condition (total mass, temperature, composition, pressure) depending on the valve timing and the current engine operating point (speed, wall temperature) for any crank angle (ie also its course).

Effective valve cross-sections are approximated by rectangular / step-shaped curves

Sections with different on / off configurations of the inlet / outlet valves are dealt with separately.

Each section can be calculated in one step from operating parameters and the final status of the previous section.

Mean value model within the section (no integration within a section)

The method is based on differential equations for the temporal change in the enthalpy of a cylinder:

i.e._C.yi / dt = Q * waii + V_cy, dp_cyi / dt + Σ H * i (1) or after reshaping one obtains:

dp_cyi / dt = 1 / V_cyi (- κ p_cyi dVc_yi / dt + (κ -1) Q *_waii + κ R Σ T, m *,) (2)

Derivation for the simplified case:

First, the following simplifications are introduced:

Constant piston speed: dV_cyi/ dt = A_O c_m (3)

Linear approach for the mass flows: m * = k_{T (i} (p, - p_cyi) (4)

Linear approach for heat flow: Q *_wan = k_w A._cyip_cyi (5)

Insertion provides:

dpc_yi / dt - Pc_yi / V_cyi (-κ A_O c_m + (κ -1) k_w A._cyi - κ R Σ T, k-rj) + κ R / V_cyi Σ pi T kyj (6)

AT 006 293 U1 mean here

H_cyi ..... enthalpy of the cylinder,

Q *_waii ..... wall heat flow,

V_cyi ..... cylinder volume,

H * j ..... enthalpy flow via i-th valve, κ ..... isentropic exponent,

R ..... gas constant and

Ti ..... temperature of the gas flowing in via i-th valve,

A._O ..... piston area, c_m ..... mean piston speed, p_cyi ..... cylinder pressure, k_w ..... heat transfer coefficient, k_{T (f} ..... linearity factor, m *, · ..... mass flow through i-th valve

The solution to the simple differential equation is:

Pcyl ^— [Pcyl, 0 P «] (Vcyl / Vc_y|, o) k + p »(7) with: poc = - (k R) / (k ~ A_O c_m) Σ p, T, k_T, i (8) k ~ = - κ + (κ -1) (k_w A._cy,) / (c_m Ao) - (k R) / (c_m Ao) Σ T, k_TJ (9)

The solution for cylinder pressure consists of two parts:

Constant pressure (negative pressure to maintain the mass flow) 'Polytrope' for the deviation from the initial condition

For the solution of the total air mass ιτίη, ι through the cylinder (2), by means of integration from equation (4), mcyi = J Σ m * i dt = J Σ k_T, i (Pi - p_cyi) dt (10)

For the derivation, simplifications were used that deviate from the real system properties and therefore have to be corrected retrospectively:

Constant piston speed Linear throttle equation

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The points of application for the corrections can be defined by comparing the approximation solution with the numerical solutions of the corresponding simple differential equations.

i) Real piston speed (for linearized throttle equation)

If, in the above solution, equation (7) is used instead of the mean piston speed c_m If the real piston speed is used, the numerical solution for low speeds can be approximated relatively precisely. In general, however, there is a need for a speed-dependent correction that simulates the delays resulting from the change in piston speed over time.

ii) Throttle equation (for constant piston speed)

Depending on the linearization rule k_T, i for the throttle equation (4) there are different pressure differences that are necessary to maintain the mass flow. The different pressures with the same volume result in deviations in the air mass. A correction can be made with the help of a conversion rule for the pressure difference calculated for the linearized case.

As an example, FIG. 4 shows how the effective valve cross section is approximated by a mean valve cross section. For this purpose, the effective valve lift H is determined by a rectangular lift curve H of the same area_m approximated. A point in time t, for example, can be used as the start or end of the sub-process_x or t₂ can be defined at which the valve stroke H of the gas exchange valve is 10% of the total stroke.

The internal combustion engine 1 shown schematically in FIG. 1 for performing the method has at least one piston 3 reciprocating in a cylinder 2, which delimits a combustion chamber 4 into which at least one inlet channel 5 and at least one outlet channel 6 open. The inlet channel 5 is controlled via an inlet valve 7, the outlet channel 6 via an outlet valve 8. An injection device 9 for fuel injection opens directly into the combustion chamber 4. As an alternative or in addition to the injection device 9, an ignition device can also open into the combustion chamber 4. Reference number 10 denotes the compressor part, and reference number 11 denotes the turbine part of an exhaust gas turbocharger. A throttle device 13 is arranged in the suction pipe 12. An exhaust gas purification system 15 is provided in the exhaust gas line 14 downstream of the turbine 11. Upstream of the turbine 11, an AbAT 006 293 Ul gas recirculation line 16 of an exhaust gas recirculation device 17 branches off from the exhaust line 14 and opens into the intake manifold 12 downstream of the compressor 10 and the throttle device 13. Reference number 18 denotes an exhaust gas recirculation valve.

A change in the arrangement of the optional components exhaust gas recirculation device 17, compressor 10, throttle device 13, turbine 11 and exhaust gas cleaning system 15 has no influence on the calculation method.

In the suction pipe 12 pressure p_L., Temperature T_L. and / or the composition of the sucked gas is measured. In the exhaust manifold of the exhaust line 14, pressure p_A., Temperature T_A. and / or composition of the exhaust gas measured. Furthermore, the parameters of the valve train of the inlet valves 7 and the outlet valves 8 are determined, namely activation times, effective flow cross-section of the inlet valves 7 and the outlet valves (as a function of the valve lift curve). The parameters of the combustion, namely control times (injection timing, ignition timing) and the fuel quantities are also determined. Furthermore, general engine operating parameters such as engine speed n and cylinder wall temperature T_w determined. Some of these operating parameters can be determined algorithmically, so that not all operating parameters actually have to be measured. A measurement of the cylinder pressure p_cyi is not required. The operating state of the internal combustion engine 1 is described by the following operating parameters: torque, mass flow, loading state of the cylinders (air mass, pressure, temperature and gas composition), energy content of the exhaust gas and wall heat flow.

According to the present method, to calculate the cycle of the internal combustion engine 1, it is divided into sub-processes 21 to 28, 31 to 38 described by simplified relationships and each state within a sub-process 21 to 28, 31 to 38 analytically from the initial state and operating parameters of the respective sub-processes 21 to 28, 31 to 38 calculated. The numerical integration of the entire cycle is thus replaced by a combination of integrals that have been separated in sections.

The calculation models are based on different assumptions and / or have different simplifications. The time limits of the sub-processes 21 to 28, 31 to 38 are calculated as a function of at least one measured engine parameter. A meaningful definition of the sub-processes 21 to 28, 31 to 38 is expediently based on the position of the inlet / outlet valves 7, 8 or the sequence of the partial burns. The following possibilities thus arise: inlet valve 7 and / or outlet valve 8 open or several inlet / outlet valves 7, 8 open simultaneously; a burn 9

AT 006 293 Ul tion or superimposition of several burns; Compression / expansion of the gas trapped in the cylinder.

FIG. 2 schematically shows a first exemplary embodiment for a cycle 20 of a four-stroke internal combustion engine, which is subdivided into several partial processes 21 to 28, with internal exhaust gas recirculation and a single combustion. The sub-processes 21 to 28 are through the process of combustion B, the expansion E, the opening 0 of the exhaust valve 8, the overlap OI of the intake valve 7 and exhaust valve 8, through the opening I of the intake valve 7 and through the compression C of the gas in the combustion chamber 4 characterized. The cycle 20 shown in FIG. 2 has residual gas recirculation by opening the outlet valve 8 again between inlet phase I and compression phase C.

3 shows a second exemplary embodiment for a cycle 30 of a four-stroke internal combustion engine with a rigid valve train, which is subdivided into several partial processes 31 to 38. The cycle 30 has two partial burns B in this case_x and B₂ on, whereby between the two partial burns Bi and B₂the sub-process 32 as the overlap phase B_ii2 between the first combustion Bi and the second combustion B₂ is defined.

The method according to the invention can be used as a physical charge model in different configurations or combustion technologies, for example both in a standard valve train and in a partially or fully variable valve train, and in different combustion models. Furthermore, models for recording the gas condition in the intake manifold 12 and for recording the gas condition in the exhaust line 14 can also be used. The models mentioned can be used individually or in combination with one another.

As part of the method, it is also possible to regulate the gas state by deliberately varying the valve control times.

Furthermore, the combustion and the exhaust gas composition with regard to CO₂, NO_X, Particles etc are regulated.

The accuracy of the calculation method can be significantly improved if calculated parameters are compared with measured parameters. In this way it makes sense to use the calculated values ​​for mass flow m_cyi, cylinder pressure p_cyi, to compare the air / fuel ratio and torque with the measured values ​​and to adjust them.

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With the method described, the operating state for any crank angle can be determined in real time independently of the configuration of the internal combustion engine 1.