DE10215674A1 - Method for operating an internal combustion engine - Google Patents

Abstract

The invention is based on a method for operating an internal combustion engine with compression ignition, in which an exhaust gas quantity retained in the combustion chamber is regulated as a function of the operating point by means of an adjustment of valve control times. With an ion current probe arranged in the combustion chamber, an ion current signal is measured, wherein the position of the 50% mass conversion point of the current combustion is determined from the ion current signal curve in order to control the course of the combustion by means of an adjustment of operating parameters in a subsequent cycle.

Description

The invention relates to a method for operating a Internal combustion engine according to the preamble of claim 1.

To comply with increasingly stringent emissions regulations newly developed self-igniting internal combustion engines with a homogeneous charge (HCCI engines), HCCI as Abbreviation for Homogenous Charge Compression Ignition. In such HCCI internal combustion engines caused by the Use of homogeneous, lean mixtures low nitrogen oxides, and it will be high thermal efficiencies at low Particle formation achieved. It can be both diesel and Otto fuels are used, wherein in use of petrol fuels in high load ranges the mixture is ignited externally.

From DE 101 22 775 A1 an internal combustion engine is known, when using a compression ignition a homogeneous charge is ignited. DE 101 22 775 A1 provides a load-dependent Self- or spark ignition before. Furthermore, it is proposed that by means of a device two camshafts variable be controlled to switch between one Compression ignition operation and a spark ignition operation to enable.

A method of operating an HCCI engine is known from DE 199 52 096 C2, in which by means of various Control variables combustion is controlled. To be in it variably controllable intake and exhaust valves and a Injection system by a control device such that, depending on a time point, the 50% Implementation of the injected fuel mass during of a cycle as correcting variables a certain air ratio, a certain effective compression, a specific one Injection pressure, a certain injection time and a certain injection quantity to determine the beginning and duration the combustion of the cylinder charge or the location of the 50% Mass sales pucks set for the next cycle become.

The heat release, in particular its beginning and course, as well as their control when using an HCCI Combustion process for the operation of the internal combustion engine of special meaning. To take advantage of an HCCI Exploiting the combustion process in wide map areas, it needs a continuous, fast as well cost-effective control of combustion processes during a driven operating point especially for avoidance an undesirably early combustion position, which too high Pressing in the combustion chamber leads, d. H. an influence on the Heat release should during operation of a HCCI internal combustion engine take place as quickly as possible, otherwise the achievement an optimal combustion can not be realized. The o. g. Documents do not provide for such a regulation.

The object of the invention is therefore to provide a method of operation an internal combustion engine, in which an improved Burning behavior of the internal combustion engine is made possible.

The task is performed by a procedure with the characteristics of Claim 1 solved.

The inventive method provides that during operation an internal combustion engine with direct fuel injection, the supply of combustion air in a combustion chamber over at least one inlet valve is controlled, the discharge exhaust gas from the combustion chamber via at least one exhaust valve is controlled. By means of a arranged in the combustion chamber Ion current probe, an ion current signal is detected with the a location of the 50% mass point at an operating point with the determined position of the 50% Mass conversion point by one in a motor control stored and operating point-dependent correction value is changed so that one by the position of the Ion current probe in the combustion chamber caused distortion or Deviation of the determined position of the 50% mass conversion point is compensated.

According to the invention, the detected ion current signal becomes the Location of a 50% mass point of current combustion determined, d. h., the time at which 50% of in the Combustion chamber injected fuel mass during a Combustion cycle or cycle is implemented. With help the determined position of the 50% mass conversion point of the current Combustion is the currently determined value with an in compared to a control unit stored value. At a the next cycle is the combustion process an adjustment of operating parameters changed so that optimum burning behavior takes place.

In an embodiment of the invention is to determine the location of the 50% mass point a mass conversion point of a used immediately preceding the combustion cycle. This allows a very fast control.

Due to the position of the ion current probe in the combustion chamber, a Distortion of the determined values at an incomplete Homogenization occur because the ion current probe only one small subset of the mixture present in the combustion chamber detected. Therefore, a load-dependent correction of the position of the 50% mass point, in order to actual value to compensate for different distortion. Such correction values are stored in a motor control and are used in adjusting the operating parameters considered.

The actual times of a 50% mass conversion point of the Combustion at a specific operating point will be for the Internal combustion engine based on a thermodynamic Combustion analysis, for example with the help of a s. G. Vibe Function determined on the test bench. At the same time by means of an ion current probe the times of the 50% Mass conversion point determined. The difference then becomes the correction values determined. Thus, for everyone Operating point determines the location of the 50% mass conversion point, in which an optimal combustion behavior takes place, and continue to set a correction value based on a Corrected ion current probe data corrected.

In a further embodiment of the invention are for determination the location of the 50% mass point the mass conversion points used several previous combustion cycles. This results in a very accurate regulation, as often in the Internal combustion engines cyclic in the same operating point Fluctuations occur.

In a further embodiment of the invention takes place in the Determining the location of the 50% mass point of several preceded by combustion averaging instead of. Thus, the erfindungemäße method provides a cost-effective alternative to controlling an HCCI Internal combustion engine.

In the operation of the internal combustion engine according to the invention first with the measured ion current signal a position or a Time of the 50% mass point for a current one Combustion cycle determined. As of this time of a actual time deviates due to the probe position, it is determined by the operating point-dependent correction value corrected. Thus, approximately the actual results Time of the 50% mass point. This in turn will be with an optimal time of the 50% mass point compared, in which the internal combustion engine in the respective Operating point has optimal combustion behavior. The Internal combustion engine is then subsequently controlled so that combustion is optimal in a subsequent cycle runs.

Preferred for combustion control Operating parameters such as valve timing and / or the Fuel injection used, over the one in the combustion chamber formed mixture is composed of fuel, Air and optionally retained exhaust exists. It can mixture characteristics such as residual gas content, air ratio and / or the mixture temperature can be varied. Furthermore, can made a variation of the compression ratio become.

According to the invention, an adaptation of the combustion variables in the subsequent combustion cycle, for example by Change in the amount of exhaust gas retained in the combustion chamber instead of. This is done optionally by means of an adjustment of Inlet and exhaust valve timing. Thus be Combustion parameters such as start of heat release, too referred to as start of combustion, and course of the Heat release controlled.

The variation of the valve timing is preferred Camshaft adjuster made, alternatively, the Variation of the valve timing by an electromagnetic Valve control or any other variable Valve control device can be done. An adaptation of the Combustion variables can also be determined by means of an injection strategy be made by changing the injection parameters, for example, the time of fuel injection, the duration of the injection, the amount of fuel injected or the injection pressures and optionally a made Timing of the injection can be modified. Conceivable is also a combination of a change of Valve timing, for example, a change in the Combustion chamber retained exhaust gas allows, and a adapted fuel injection strategy to at a following cycle to the combustion process influence, and thus by means of the modification an optimal To achieve burning behavior. This may be the adaptation of the Combustion settings according to the invention over several Extend combustion cycles.

In a particularly advantageous embodiment, the HCCI Combustion process in a spark-ignition internal combustion engine with used a direct fuel injection. An HCCI Operation takes place in the lower and middle load range, whereby in the high load and full load range spark ignition takes place. The electrodes of the spark plug are used in HCCI mode next to their ignition function in Otto engine operation as a sensor for detecting a degree of ionization in the combustion chamber.

According to another embodiment, the HCCI Burning method used in a diesel engine, depending on Load point either a conventional diesel combustion or HCCI operation takes place. A arranged in the combustion chamber Glow plug is then used in HCCI operation as an ion current probe for Detection of an ion current signal.

The invention is based on the drawing, the Embodiments of the invention, in the following description explained in more detail. Show it

Fig. 1 is a schematic representation of a reciprocating internal combustion engine with a control unit, one injector and means for adjusting the valve timing,

Fig. 2 is a diagram with a measured ion current signal and its integral, and other thermodynamic parameters of the combustion, and

Figure 3 is a diagram for comparison of the 50% -. Mass conversion point is calculated from an ion current integral and the 50% -Massenumsatzpunkts calculated from the heat curve or from the Vibe function.

In Fig. 1, a reciprocating internal combustion engine 1 is shown schematically. It comprises four cylinders 2 , in which pistons not shown are guided and which are closed by a cylinder head, not shown. Cylinder 2 , piston and cylinder head surround a combustion chamber 3 , in which the combustion of a fuel injected into the combustion chamber by a fuel injector 4 takes place. At least one fuel injector 4 , an inlet valve 5 , an outlet valve 6 and a spark plug 10 are arranged in the cylinder head per combustion chamber 3 . The fuel injector 4 is driven by an injection device 7 . The fuel injection times and possibly a load-pending timing are controlled by signals from a controller 9 by means of the injector 7 .

A variable valve control device 8 comprises an unillustrated actuator for the intake and exhaust valves 5 , 6 , which serves to vary the valve timing. This may be a mechanical, hydraulic or electric camshaft adjuster, wherein alternatively an electromagnetic valve control unit or any other variable valve control unit may be used. Depending on the system used, this may include one or more camshafts with phasing actuators, or switchable bucket tappets with variable valve lift limitation or roller articulated levers with variable articulation point as well as different cams with switching systems similar to the so-called VTEC system and at least one exhaust throttle valve.

In Otto engine operation, the ignition of the mixture takes place through the spark plug 10 , wherein an amount of air supplied to the combustion chamber 3 is controlled by an intake throttle valve, not shown. In HCCI operation, the mixture of retained exhaust gas, fuel and air is compressed, with combustion initiated by compression ignition.

The control unit 9 is used to control the internal combustion engine 1, ie it controls the spark plug, the opening and closing operation of the fuel injector 4 and the intake and exhaust valves 5, 6 by means of the variable valve control device. 8 In the operation of the internal combustion engine 1 , the mixture is ionized, wherein a degree of ionization of the mixture components as well as the temperature is dependent. Due to the degree of ionization, an ionic line can be measured.

The arranged in the combustion chamber 3 spark plug 10 is used in HCCI operation by applying an electrical voltage to the electrodes of the spark plug 10 for detecting an ionic current signal, which is supplied to the control unit 9 and used for determining the center of gravity of the combustion. Alternatively, the measurement of the ion current signal by an additional ion current probe in the combustion chamber 3 take place. The real-time signals supplied to the control unit 9 provide information about the position and the course of the combustion. The controller 9 compares the detected values such as the position of the 50% mass conversion point of the current combustion with values stored in a map, and effects the control of the fuel injector 4 and the variable valve control device 8 , taking into account the actual values, as necessary Adjust combustion in a subsequent combustion cycle. The control unit 9 controls z. B. in a non-optimal combustion process, the camshaft adjuster such that the retained in the combustion chamber 3 exhaust gas amount is changed, so that a different mixture temperature is adjusted, whereby the combustion position is optimized.

The above method makes it possible to determine the position of the 50% mass conversion point of the combustion by means of an integral of the ion current waveform with the aid of the spark plug 10 used as an ion current probe. The location of the 50% mass conversion point changes with respect to the crank angle when the combustion history changes, as shown in FIG . Is 50% of the energy supplied, z. B. as a calculated heating process implemented, so there is the 50% - mass conversion point. Fig. 2 illustrates the course of an ion current signal X in the combustion chamber 3 of the internal combustion engine 1 and a calculated from a measured cylinder pressure curve heat curve Y plotted against the crank angle K of the internal combustion engine 1. Recognize let the curves shown that the integral of the locally measured ion current very well correlated with the Heizverläufen, especially at 50% of the supplied energy, in Fig. 2 referred to as mass conversion M. Furthermore, the mass conversion M calculated by means of a Vibe_Function F is shown as a further comparison.

In the case of the internal combustion engine 1 , the ion current signal X measured in the combustion chamber 1 has a characteristic profile which correlates directly with the combustion process, ie the heat release of the internal combustion engine 1 . This detected signal is used directly to determine a position of the 50% mass conversion point of the current combustion, resulting in a very short reaction time with regard to the regulation of a subsequent cycle in order to achieve the fastest possible adaptation of the operating parameters. There is an integration of the ion current signal X instead. The ion current waveform is summed or integrated, the integral maximum or the total corresponding to a 100% conversion of the fuel mass that has participated in the combustion in each cycle. The processing of the signal in a control unit takes place within a very short time, whereby the internal combustion engine 1 can always be operated at an optimum operating point. This means that a complex control unit is not needed.

According to FIG. 2, the course of the ion current integral Xi at the time of the 50% mass conversion point has a deviation Δ compared with the calculated heating curve Y. This deviation is due to the position of the ion current probe 10 in the combustion chamber 3 . In order to determine the actual position of the 50% mass conversion point, the time determined by the ion current probe 10 is corrected by a correction value which corresponds to the deviation Δ. This results in the actual location of the 50% mass conversion point, which can be used to control combustion in terms of combustion and heat release. The internal combustion engine 1 is controlled within a short period if necessary so that it can be optimally operated at the respective operating point.

In determining the location of the 50% mass point of a certain combustion cycle will be measured values of a used immediately preceding the combustion cycle. As a result, a very fast control is achieved. To one to achieve more accurate regulation are alternatively in the Determining the location of the 50% mass point multiple preceding combustion cycles, preferably 5 to 20 or 10 to 30 cycles used. In that case, d. H. in the Using several previous combustion cycles, finds a moving average takes place in which an average of the previous cycles is formed.

Fig. 3 shows the correlation of the detected 50% - mass conversion points K _f, the Vibe a function are calculated using, and those 50% mass conversion points K _x that are determined from the ion current signal. The correlation shows that the heat release of the internal combustion engine 1 can be determined from the ion current signal. Thus, a control of the combustion processes with regard to the start of combustion, heat release and location of the 50% mass conversion point is made possible. As further control variables z. As load, speed, combustion chamber wall temperature, intake air temperature, and / or intake air pressure serve.

Claims (12)

1. A method for operating an internal combustion engine with a direct fuel injection, in which
the supply of combustion air into a combustion chamber is controlled via at least one inlet valve,
the removal of exhaust gas from the combustion chamber is controlled via at least one outlet valve,
an ion current signal is detected with an ion current probe arranged in the combustion chamber,
determining from an ion current waveform a position of the 50% mass conversion point at an operating point,
characterized in that
the determined position of the 50% mass conversion point is changed by a correction value stored in a motor control and operating point-dependent, so that a distortion or deviation of the determined position of the 50% mass conversion point caused by the position of the ion current probe in the combustion chamber is compensated. 2. The method according to claim 1, characterized in that for Determine the location of the 50% mass point Mass conversion point of an immediately preceding Combustion cycle is used. 3. The method according to claim 1, characterized in that the Determination of the location of the 50% mass conversion point Mass sales points of several previous ones Combustion cycles are used. 4. The method according to claim 3, characterized in that at determining the location of the 50% mass point several preceding combustion cycles a sliding one Averaging is taking place. 5. The method according to any one of claims 1 to 4, characterized characterized in that the course of combustion of a subsequent combustion cycle to achieve a optimal combustion in each operating point based the determined location of the 50% mass conversion point so that operating parameters such as characteristics of an im Brennraum formed mixture by a variation of Valve timing and / or a fuel injection Adjusted accordingly. 6. The method according to any one of claims 1 to 5, characterized characterized in that by the variation of Valve timing and / or an adjustment of Injection strategy during the subsequent combustion cycle a change of a retained in the combustion chamber Exhaust gas quantity takes place. 7. The method according to any one of claims 1 to 6, characterized characterized in that the variation of the valve timing by adjusting the phase position of one or more Camshafts done. 8. The method according to any one of claims 1 to 6, characterized characterized in that the variation of the valve timing by an electromagnetic or hydraulic Valve control takes place. 9. The method according to any one of claims 1 to 8, characterized characterized in that the adaptation of Operating parameters over several combustion cycles extends. 10. The method according to any one of claims 1 to 9, characterized in that the internal combustion engine optionally with Compression ignition is operated. 11. The method according to any one of claims 1 to 10, characterized characterized in that arranged in the combustion chamber Ion current probe for detecting the ion current signal as Spark plug is designed. 12. The method according to any one of claims 1 to 10, characterized characterized in that arranged in the combustion chamber Ion current probe for detecting the ion current signal as Glow plug is configured.