DE102006016905A1 - Process for operating an internal combustion engine, especially for determining combustion chamber pressure, comprises modeling the combustion chamber pressure on previously determined operating variables - Google Patents

Abstract

Process for operating an internal combustion engine, especially for determining combustion chamber pressure, comprises modeling the combustion chamber pressure on previously determined operating variables. Preferred Features: A linear model is used. The combustion chamber pressure is modeled only in critical operating regions. The injection parameters for fuel injection are changed when an overshoot of the maximum permissible combustion chamber pressure is imminent.

Description

The The invention relates to a method for operating an internal combustion engine, in particular, for a diesel engine, a maximum value for a combustion chamber pressure not to exceed according to the preamble of claim 1.

From the German patent application DE 29 39 590 A1 a method for operating an internal combustion engine is known, in which a combustion chamber pressure is detected according to size and crankshaft angle position. The detected course of the combustion chamber pressure is differentiated and zero crossings of the derivative are detected. At the first zero crossing, the occurrence of the peak pressure is assumed and the associated crankshaft angle is detected. Depending on the crankshaft angle position of the peak pressure operating parameters of the internal combustion engine are regulated.

components internal combustion engines are subject to statistical variations in their dimensions. Therefore, there are upper and lower limit pattern motors, which are the corner points form an approved range of limiting farm sizes. In the diesel engine, the spread of the combustion chamber peak pressure is especially a limiting size, because when exceeded upper permissible limit of peak pressure the limit of loading exceeded the diesel engine becomes. With an approved combustion chamber tip pressure of 200 bar with a dispersion of 20 bar, the construction of the diesel engine only be designed to 180 bar setpoint, even at a upper limit pattern motor does not exceed the load limit.

From the European patent application EP 1 203 875 A1 a method for protecting an internal combustion engine from overpressure is known in which the combustion pressure in at least one cylinder of the internal combustion engine is measured. When the peak pressure in a cylinder of the internal combustion engine exceeds a predetermined threshold value, the fuel introduction and / or the fuel combustion should be modified differently from the values predefined by the engine control so that the peak pressure remains below the threshold in subsequent cycles.

From the German patent application DE 197 05 463 A1 a method for controlling an internal combustion engine is known in which a peak pressure in the combustion chamber is detected by means of a combustion chamber pressure sensor. If the combustion chamber pressure reaches a limit, the start of injection is adjusted so that the combustion chamber pressure drops.

From the German patent DE 39 33 947 C1 a method for determining the combustion pressure in reciprocating engines is known in which by means of an acceleration sensor on at least one crankshaft bearing of the reciprocating engine, the acceleration occurring at the crankshaft bearing is determined. By means of the detected acceleration, the combustion pressure is determined indirectly. From the time course of the acceleration values, pressure rise and peak pressure of the combustion pressure can be determined. Controlled variables for quantity, mixture, filling, injection and ignition timing control can be derived from the increase in pressure and peak pressure determined by means of the acceleration measurement.

Out This prior art shows that the effort to determine a combustion chamber pressure on sensors and evaluation comparatively is high and therefore causes high costs. Therefore, one tries on the basis of existing operating variables on the current combustion chamber pressure close.

This is from the German patent DE 102 20 320 B3 a method for operating an internal combustion engine, in which steps are provided for detecting operating variables of the internal combustion engine and for setting operating parameters of the internal combustion engine as a function of the detected operating variables, and in which it is checked whether the values of the detected operating variables and / or combinations of these values indicate a deviation of a combustion chamber peak pressure from a predetermined maximum value.

Of the Invention is the object of this known method educate, so that during the operation of the internal combustion engine, the combustion chamber pressure without immediate Capture more accurately estimated can be.

Is solved this object by a method with the specified in claim 1 Characteristics, for operating an internal combustion engine, in particular for determining a combustion chamber pressure. According to the invention, it is proposed that modeled on the basis of already recorded operating variables of the combustion chamber pressure becomes.

The inventive method points opposite The prior art has the advantages that even without sensory Always capture an exact size of the combustion chamber pressure is present and thus also under unfavorable (transient) operating conditions while driving, for example in cold operation or at high speeds and simultaneously going up to a higher gear, exceeding a known maximum allowable combustion chamber pressure by changing reliably prevented from operating variables can be.

at a preferred embodiment of the invention according to claim 2 is proposed that the modeling of the combustion chamber pressure a linear model is used. This measure leads to a far less elaborate Parameterization. The linear model is invertible and fast to calculate so that the parameters to be limited calculated directly can be.

To a further advantageous embodiment of the invention according to claim 3 it is provided that the combustion chamber pressure only in critical operating areas is modeled. This proposal also leads to less programming effort and reduces the amount of computation and memory required so that the associated Software easily implemented in the engine control unit and executed there can.

A advantageous embodiment the invention is characterized according to claim 4, characterized in that in case of imminent exceeding the maximum allowed Combustion chamber pressure the injection parameters of the fuel injection to be changed. changes at the fuel injection parameters without additional Effort possible and have a very fast effect, ie already in the next working game. The is called, it can be intervened very quickly as soon as the combustion chamber pressure at its maximum allowable maximum value approaches.

In a further development of the invention according to claims 5 to 7 is provided, in each case a value for an electrical delivery start and for one maximum permissible electrical delivery start to calculate and the calculated value for the electrical delivery start up to an applicable limit value the calculated maximum permissible electrical start of delivery tracked becomes.

Of the electrical start of delivery, in particular the time of the electrical control of an injector valve, is an important influencing parameter for the combustion chamber pressure. He has the advantage over other influencing parameters that he specified very accurately by the engine control unit can be. It is based on the model of the maximum allowable electrical Start of delivery, just not to exceed the peak pressure limit leads, certainly. However, the electric delivery start to be set becomes the maximum permissible electrical start of delivery tracked only up to an applicable limit to not to change the engine tuning too much.

Around also in the case that the electrical delivery start to be set would have to track more than the applicable limit, the maximum permissible Not to exceed combustion chamber pressure, will continue in a preferred device according to claim 8 proposed that the injection quantity is limited.

The Injection quantity is another influencing parameter for the combustion chamber pressure and can be comparable to the electric delivery start without additional Effort to be set. On the changeability of the injection quantity is accessed in particular when the value for the electric start of delivery not changed can or should be. Thus, the modeling yields a value for the one to be set electrical start of delivery, by more than the applicable limit of one calculated in the engine control unit desired Value deviates, so will for the value to be set for the electrical delivery start the maximum allowed electrical delivery start fixed (by the minimum selection proposed in claim 9) and limits the injection amount (e.g., in the form of the delivery time). Consequently is ensured that the allowed Maximum value for the combustion chamber pressure is not exceeded becomes.

Finally will according to claim 9 nor suggested that a minimum selection between the value for the electrical delivery start and the maximum allowable Value for the electrical delivery start is made.

By this minimum selection becomes the smaller of the two compared values set as the actual value and as a further measure to the maximum allowable combustion chamber pressure not to exceed further limits or reduces the injection quantity (as in Proposed patent claim 8).

Further advantageous embodiments of the invention are in further claims, the Description or the figures indicated.

The Invention will now be described with reference to an embodiment with the aid explained the drawing.

there the figure shows a schematic block diagram with function blocks for Determination of a fuel delivery start with application of the method according to the invention.

The Invention is particularly suitable for operating an internal combustion engine, in particular, in a diesel engine, a maximum value for a Combustion chamber pressure not to be exceeded.

The figure shows a schematic block diagram 1 for determining a fuel delivery start FB is with application of the method according to the invention.

In certain operating conditions (eg In stationary operation, cold operation), ie in critical operating _ranges , a maximum permissible combustion chamber _pressure p _{max_zul} can be exceeded in the prior art. To prevent this, a current combustion chamber pressure p must be known.

p

Brennraumdruck,

FB

Förderbeginn (Kraftstoff),

t_2s

Ansauglufttemperatur (im Saugrohr),

p_2s

Ladeluftdruck,

FD

Förderdauer und

a, b, c, d

lineare Koeffizienten.

Investigations have shown that the actual actual combustion chamber pressure p for individual load points can be approximated well by a linear model. The linear equation for the current combustion chamber pressure p is: p = a * FB + b * t 2s + c · p 2s + d · FD, with the following variables:

p

Combustion chamber pressure,

FB

Start of delivery (fuel),

t _2s

Intake air temperature (in the intake manifold),

p _2s

Charge air pressure,

FD

Duration of funding and

a, b, c, d

linear coefficients.

The quantities intake air temperature t _2s and charge air pressure p _2s are sensed and are already present in an engine control unit. The sizes start of delivery FB and delivery time FD are usually stored depending on the operating point in a map in the engine control unit. The coefficients a, b, c and d are determined for a particular engine based on bench tests. In the exemplary embodiment of the figure, there is now the case that as a variable for certain operating points of the beginning of delivery FB_ist is to be determined from the above equation.

For this purpose, maps stored in (not shown) engine control unit maps 2 . 3 . 4 and 5 for example, linear coefficients a, b, c and d are accessed and the respective size is a function block 6 fed. The coefficients a, b, c and d can also be determined as a function of rotational speed, for example.

From another map 7 becomes the function block 6 In addition, an operating-point-dependent maximum permissible combustion chamber pressure p _{max_zul} supplied. From the coefficients a, b, c and d, the sensed quantities t _2s and p _2s , the requested delivery time FD from the engine and the maximum permissible combustion chamber _pressure p _{max_zul} (eg 180 bar), a limit value is determined on the basis of the above equation for the start of funding, the limit funding start FB_grenz determined. This limit promotion start FB_grenz becomes another function block 8th fed.

In a further functional block 9 in the engine control unit, the calculation of a setpoint for the start of delivery, the desired delivery start FB_soll; the result for the target delivery start FB_soll is the function block 8th fed. In another function block 10 the calculation of a delivery time FD_soll as a measure of a fuel quantity takes place; the result for the delivery time FD should also be the function block 8th fed.

In the function block 8th First, the limit feed start FB_limit from the function block 6 with the target delivery start FB_soll from the function block 9 compared. In the event that FB_setpoint is greater than FB_limit, the setpoint start of delivery FB_setpoint will be tracked to the limit start of delivery FB_limit, but only up to an applicable limit value (further adjustment would disturb engine tuning). Should it be necessary to track beyond the applicable limit value (in order not to exceed the maximum permissible combustion chamber pressure), the desired delivery start point FB which should be tracked by the applicable limit value should be considered to be a start of delivery actually to be set 11 FB_ist is set and, in addition, a limitation or reduction of the previously calculated delivery time FD soll (function block 10 ) to a delivery time FD actually to be set is 12.

In the event that FB_soll is smaller than FB_grenz takes place in the function block 8th a minimum selection between the limit start of delivery FB_grenz and the desired start of delivery FB_soll. This prevents that the target delivery start FB_soll exceeds the limit delivery start FB_grenz (which would lead to exceeding the maximum combustion chamber pressure).

The smaller of the two values then becomes the actual start of delivery 11 FB_is set.

By the modeling according to the invention of Combustion chamber pressure based on already existing in the engine control unit Sizes are unnecessary the difficult and time-consuming sensory detection of this size.

Claims (9)

Method for operating an internal combustion engine, in particular for determining a combustion chamber pressure, characterized in that based on already recorded operating _variables (t _2s , P _2s ) the combustion chamber pressure (p) is modeled. Method according to claim 1, characterized in that that the modeling of the combustion chamber pressure (p) is a linear model is taken as a basis. Method according to claim 1 or 2, characterized that the combustion chamber pressure (p) only in critical operating ranges is modeled. Method according to one of Claims 1 to 3, characterized in that when the maximum permissible combustion chamber _pressure (p _{max_zul} ) is _exceeded, the injection _{parameters of} the fuel injection (FB, FD) are changed. Method according to Claim 4, characterized in that a value for an electrical delivery start ( 9 , FB_soll) is calculated. A method according to claim 4 or 5, characterized in that a value for a maximum allowable electrical delivery start ( 6 , FB_limit) is calculated. A method according to claim 5 and 6, characterized in that the calculated value for the electrical delivery start ( 9 , FB_set) up to an applicable limit value of the calculated maximum allowable electrical delivery start ( 6 , FB_grenz) is tracked. A method according to claim 7, characterized in that a desired injection quantity (FD_soll) is limited or reduced, if the calculated value for the electrical delivery start ( 9 , FB_set) would have to be tracked by more than the applicable limit value. A method according to claim 7 or 8, characterized in that a minimum selection between the value for the electrical delivery start ( 9 , FB_set) and the maximum permissible value for the electrical delivery start ( 6 , FB_limit), if the setpoint for the start of delivery ( 9 , FB_set) is less than the maximum permitted start of production ( 6 , FB_limit).