DE10328789A1 - Method and device for pressure wave compensating control of an injection system of an internal combustion engine - Google Patents

Abstract

at a method and a device for controlling an at least two injection elements having injection system of an internal combustion engine, wherein the fuel metering into a first partial injection and at least a second partial injection is divided and wherein one to be injected by means of the at least two injection elements Fuel quantity determining control signal in response to a pressure wave influence the at least two partial injections are corrected is provided that for the at least two Einseititzelemente a collective pressure wave correction carried out and a collective correction function is determined that individual parameters of at least two injection elements are detected and that the collective correction function by means of the detected individual characteristics of the at least two injection elements is amplitude modulated.

Description

The The invention relates to a method and a device for controlling an injection system of an internal combustion engine according to the preambles of respective independent Claims.

In modern high-pressure fuel injection systems, in particular self-igniting internal combustion engines, the entire fuel quantities injected by injection valves (injectors) into combustion chambers of the internal combustion engine are each divided into a number of partial injections. These partial injections are often in a very close temporal distance from each other and usually consist of one or more temporally applied before a main injection actual pre-injection (s). A very common, in the DE 100 02 270 C1 described injection system of the type concerned here is the so-called "common rail injection system", in which fuel in a high pressure accumulator (rail) is cached before it is fed to the individual injectors.

The mentioned multiple partial injections allow improved mixture preparation and thus cause in particular lower exhaust emissions of the internal combustion engine, a reduced noise during combustion and an increased power output of the internal combustion engine.

at the said partial injections comes the accuracy of the respective Injection quantity large Meaning too. However, at the same time it is known that every injection by means of a said injector a brief onset of Fuel pressure in a arranged in the injection system supply line from the rail to the relevant injector, and in such Injector itself from a high-pressure connection adjacent to the rail to a nozzle needle of the injector means. Such a brief pressure drop causes after completion of the control of the injector, a preferred between occurring the rail and the injector fuel pressure wave. These Pressure wave leads in particular too unwanted Variations in the amount of fuel to be injected, in each case This pressure wave effect even with increasing stroke frequency the nozzle needle reinforced the injector, so that its attention in particular in future injection systems, where high-speed piezo actuators as injection actuators for nozzle needle control be used in the respective injector, even an even increasing Meaning.

A known per se approach to minimizing the pressure wave influence mentioned is to measure this outside the driving operation of a here affected internal combustion engine motor vehicle (off-line, so to speak) on a test bench and the results of this measurement, for example. In the default setting of the operating parameters of the internal combustion engine However, the model to be used in the calculation of the influence of such a pressure wave from partial injections on respective subsequent partial injections is very complex, as in this model a large number of operating parameters of the internal combustion engine, such as the injection quantity occurring in the rail Currently, the fuel pressure prevailing, the fuel temperature or the line geometries of the entire injection system ein.Es find these parameters input into the parameterization of the aforementioned, quasi "off-line" carried pressure wave enver measurement. The pressure wave correction itself then takes place by means of suitable changes in the actuation durations of the injectors, wherein a correction determined collectively for all injectors is applied to each individual injector. By means of this correction, the effect of a pressure wave on an injection of about +/- 4 mm ³ reduces to about +/- 1 ... 2 mm ³ .

As soon as however larger deviations of Injection quantities occur and / or a quantity equalization Injektor-individual drive times is made, the Amplitude of the triggered Pressure oscillations increase significantly, so that the aforementioned pressure wave correction means a rigid compensation function to a renewed deterioration the mixture preparation and thus ultimately to increased emissions and combustion noise leads. Because larger injection quantity differences to lead In addition, the end of injection deviates significantly from the respective setpoint. The pressure wave triggered by the respective injection end dominates the total occurring pressure oscillations, so that the aforementioned controlled Correction leads to significant injection quantity errors.

Advantages of the invention

Of the The present invention is therefore based on the object, a method and to develop a device of the type mentioned at the outset, that one opposite the prior art and in particular in the said operating situations the internal combustion engine improved the aforementioned pressure wave correction is possible.

The task is solved by the features the independent claims. Advantageous embodiments and further developments are the subject of the respective subclaims.

Of the Invention is based on the idea, the pressure wave correction for each Injector individually by means of an injector-individual amplitude modulation from for perform all injectors collectively determined correction data. With In other words, it proposes, in a first approximation, a collective pressure wave correction perform and the correction data determined in a second approximation by means of suitable amplitude modulation to the respective injectors individually adapt.

In a preferred embodiment of the method according to the invention will be first for all injectors the injection system collectively carried out a pressure wave correction and one for all Injectors representative first correction function determined. From a suitable sensor or an engine control unit Injector-specific parameters or operating variables are provided. When individual injector parameters come preferably the setting ratio Drain / inlet of a drain / inlet throttle or the opening pressure an injection nozzle an injector into consideration.

alternative can also in a conventional manner an actual quantity comparison of individual Injectors performed and the resulting injector-individual match data used in the manner mentioned as injector-specific parameters become.

In In another embodiment, the detected injector-specific Characteristics normalized and injector-individual values from the normalized correction quantities for the calculated amplitude modulation of the first correction function. Starting from the first correction function will then be for each Injector individually an amplitude modulated correction function calculated by means of finally the pressure wave correction of the activation times of the individual injectors can be done.

The Correction data of said for each injector individually calculated correction function preferably each transmitted in the form of control code to an engine control unit, which in this embodiment then the said pressure wave correction performs.

The The invention further relates to a device for controlling an injection system in particular in the aforementioned manner, which in a preferred Training means, by means of which a fuel quantity to be injected determining control signal in dependence from a pressure wave influencing of said partial injections is corrected, means for performing a collective pressure wave correction for the at least two injection elements and for determining a collective Correction function, means for recording individual characteristics of the at least two injection elements and amplitude modulation means the collective correction function by means of the detected individual Characteristics of the has at least two injection elements.

The method and the device according to the invention make it possible to individually correct the injection quantity behavior for multiple, temporally successive partial injections for each injector, in particular independently of the respectively prevailing pressure wave amplitude. In this case, even with stronger pressure oscillations, a precise and effective pressure wave correction is made possible by means of which very narrow injection quantity tolerances can be realized and in which the abovementioned operating characteristics of the internal combustion engine, in particular the emissions and the combustion noise, are likewise optimized. By virtue of the procedure according to the invention, the aforementioned scattering of the injection quantities of 1... 2 mm ^{3 can} even be reduced to 0.5... 1 mm ³ .

The Invention is preferred in one by means of high-speed piezoelectric actuators driven common-rail injection system with the advantages mentioned can be used, both in temporally successive applied Pre and main injections as well as applied accordingly successively individual pilot injections.

drawing

The Invention will be described below with reference to preferred embodiments and explained in more detail with reference to the drawing, from which further features, features and advantages of the invention emerge.

in the Show individual

1 a schematic representation of a known in the art common rail injection system;

2 a schematic, fragmentary view of a fuel injection valve for internal combustion engines in longitudinal section according to the prior art;

3 an injection scheme known in the prior art with a main injection and a pilot injection on the basis of corresponding control signals of an injection actuator, in particular for Il Lustration of the underlying in the invention pressure wave effect;

4a . 4b typical pressure waveforms in a in the 1 shown common rail injection system ( 4a ) as well as typical fuel flow curves for illustrating the pressure wave correction according to the invention ( 4b ); and

5 a flowchart for further illustrating the invention.

description

In the 1 For the understanding of the invention required components of a high-pressure-based fuel injection system are shown using the example of a common rail system. With 1 is a fuel tank called. The fuel tank 1 is to pump fuel through a first filter 5 as well as a prefeed pump 10 with a second filter 15 in connection. From the second filter 15 From the fuel passes via a line to a high-pressure pump 25 , The connecting line between the second filter 15 and the high pressure pump 25 also has a low pressure limiting valve 45 having connecting line with the reservoir 1 in connection. The high pressure pump 25 stands with a rail 30 in connection. The rail 30 is also referred to as (high pressure) memory and in turn is on fuel lines with different injectors 31 in pressure-conductive connection. Via a pressure relief valve 35 is the rail 30 with the fuel tank 1 connectable. The pressure relief valve 35 is by means of a coil 36 controllable.

The pipes between the outlet of the high-pressure pump 25 and the inlet of the pressure relief valve 35 are referred to as "high pressure area." In this area, the fuel is under high pressure.The pressure in the high pressure range is measured by means of a sensor 40 detected. The pipes between the fuel tank 1 and the high pressure pump 25 are referred to as "low pressure area".

A controller 60 acts on the high pressure pump 25 with a drive signal AP, the injectors 31 each with a drive signal A and / or the pressure relief valve 35 with a drive signal AV. The control 60 processes different signals from different sensors 65 characterizing the operating state of the internal combustion engine and / or of the motor vehicle which is driven by this internal combustion engine. Such an operating state is, for example, the rotational speed N of the internal combustion engine.

That in the 1 shown injection system works as follows: The fuel, which is in the fuel tank 1 is, by means of the feed pump 10 through the first filter 5 and the second filter 15 promoted through. If the pressure in the low pressure range rises to impermissibly high values, the low pressure limiting valve opens 45 and gives the connection between the output of the feed pump 10 and the reservoir 1 free.

The high pressure pump 25 promotes the amount of fuel Q1 from the low pressure area to the high pressure area. The high pressure pump 25 builds in the rail 30 a very high pressure. Usually, maximum pressure values of about 30 to 100 bar are achieved in injection systems for spark-ignited internal combustion engines and maximum pressure values of about 1000 to 2000 bar in the case of self-igniting internal combustion engines. By means of injectors 31 The fuel can thus be metered under high pressure to the individual combustion chambers (cylinders) of the internal combustion engine.

By means of the sensor 40 the pressure P in the rail or in the entire high pressure range is detected. By means of the controllable high-pressure pump 25 and / or the pressure relief valve 35 the pressure is regulated in the high pressure area.

As pre-feed pump 10 Usually electric fuel pumps are used. For higher flow rates, which are particularly required for commercial vehicles, also several parallel feed pumps can be used.

In the 2 is one of the DE 100 02 270 C1 outstanding piezoelectrically driven injection valve (injector) 101 shown in more detail in a sectional drawing. The injection valve 101 has a piezoelectric unit 104 for actuating one in a bore 113 a valve body 107 axially displaceable valve member 103 on. The injection valve 101 also has one to the piezoelectric unit 104 at adjoining actuator piston 109 and one to a valve closure member 115 adjacent actuating piston 114 on. Between the pistons 109 . 114 is a working as a hydraulic transmission hydraulic chamber 116 arranged. The valve closure member 115 acts with at least one valve seat 118 . 119 together and separates a low pressure area 120 from a high pressure area 121 , An only schematically indicated electrical control unit 112 provides the driving voltage for the piezoelectric unit 104 , depending on the prevailing pressure levels in the high pressure area 121 , In the high pressure area 121 of the injection valve 101 are also an outlet throttle 130 and an inlet throttle 131 arranged. The setting ratio drain / inlet of these two throttle 130 . 131 is by means of a control valve 132 set.

In the 3 are typical Ansteuersignalverläufe for a in the 2 shown injector in the case of a main injection 200 and a temporally preceding pilot injection 205 shown. The five signal curves shown represent different timing drive states in which the time interval between the two drive signals 200 . 205 , as seen from top to bottom, is gradually reduced to a minimum delta_t_min. In the present case, it is now assumed that the temporal distance delta_t_start resulting from the application is selected such that one through the pilot injection 205 caused pressure wave in the rail to the control of the main injection 200 has subsided again. Corresponding values are already known per se in the form of empirical values. It is further assumed that the time difference delta_t_min between the injections shown in the lowermost curve corresponds to a minimum time interval at which the time required by the pilot injection 205 already effected pressure wave to a measurable change in an operating characteristic, preferably to a change in torque of the internal combustion engine leads.

It is understood that in the 3 shown two injections serve only for illustrative purposes and therefore the method and the device according to the invention are also applicable to the temporal application of multiple injections, which of course may affect individual, temporally adjacent pilot injections due to pressure waves in the manner described herein.

The above-mentioned pressure wave effect can be determined by the 3 explain as follows. Is the pre-injection, VE ' 205 sufficiently far in time from the main injection, HE ' 200 removed, in the present case with the distance delta_t_start, so the pressure wave triggered by them is up to the main injection 200 already decayed and thus no longer has an effect on the amount of fuel injected during the main injection. This time interval is, inter alia, because of the known pressure-dependent shaft speed substantially dependent on the currently present in the rail rail pressure. An empirically determined suitable output value for delta_t_start is> 2 ms. If now the said time interval is varied by the start of the control of the main injection remains constant, but the pilot injection is brought closer to the main injection in time, so there is a influence on the main injection from a certain distance, since due to the pressure wave, the pressure in particular in the region of the nozzle needle is increased at the time of opening and during the opening of the nozzle needle either due to a wave crest of the pressure wave or lowered due to a wave trough. This results in a quantity or torque effect that can be sensed, for example, by means of a speed signal of the internal combustion engine. Alternatively, the sensing of the quantity effect in a conventional manner via a lambda probe or its control is possible.

In the 4a are typical pressure waveforms p_Injektor in the range of an injector in the 1 shown common rail injection system over time. The preinjection applied by a time prior to a main injection (or possibly a pilot injection) consists of two parts: a primary pressure oscillation 320 and a secondary pressure oscillation 330 , Starting from a pressure p_Rail prevailing within the rail 300 becomes the primary pressure vibration 320 by opening in the 2 shown switching valve 103 at the time, t1 ' 305 and is caused by the ratio of the flow restrictor / intake throttle of a throttle check valve (so-called "A / Z value"). On the other hand, the secondary pressure vibration is based on the opening 310 and closing 315 the nozzle needle of an injector at the times, t2 'and' t3 '. Due to the closing of the nozzle needle at the time t3 ', in the present case there is additionally a short-term pressure overshoot 325 ,

The mentioned throttle check valves serve in the present case for throttling the fuel flow in the Injectors. They limit the flow in a manner known per se in one direction and allow free return in the opposite direction. Depending on the installation position of the check valve the throttling effect can take place in the inlet or outlet. The modification from inlet to outlet control, for example, by turning the check valve 180 ° around one predetermined axis.

In the 4b are typical fuel flow curves m_Einspr shown in the injection to illustrate the pressure wave correction according to the invention. In the diagram, the instantaneous injection quantity is plotted in an injector over the difference time t_diff. The difference time t_diff is defined by the time interval between the descending edge of the present rectangular injection quantity profile and the rising edge of a subsequent correspondingly rectangular injection quantity profile. The solid line 400 represents the time course of the already mentioned, in a conventional manner determined collective mean value of the injection quantity of all injectors. In contrast represent the two dashed line shown 405 . 410 two scaled by means of the amplitude modulation described herein sets of quantities, which directly to correct the injection quantities of the two be be taken on the basis of impacted injectors. In the present example, the quantity curve corresponds 405 an amplitude reduction with respect to the central course 400 and the quantity flow 410 a corresponding increase in amplitude and serves, as already stated, only for illustrative purposes.

The actual pressure wave correction of the control data or control signals of the individual injectors finally takes place in a manner known per se by means of suitable changes in the activation periods. In the 4b is for illustration in addition to the periodically variable flow rates 405 . 410 a center line m_mittig located. At this value, which represents the volume curves not influenced by the aforementioned pressure wave, the oscillation curves shown have been previously normalized, so that only the relative changes with respect to this center line have to be taken into account. At time t1 ', the quantity curves describe 405 . 410 For the two injectors with respect to the center line in the middle a undershoot behavior. Therefore, the drive durations at this time are for the one with the curve 410 corresponding injector accordingly the arrow 415 to correct upward. Accordingly, the present invention substantially less correction for the with the curve 405 corresponding injector according to the arrow 420 , At time t2 ', the conditions are reversed insofar as the corrections due to the local overshoot behavior have to take place with the opposite sign. This is done at the curve 410 a correction according to the arrow 425 and at the bend 405 a turn much smaller correction according to the arrow 430 ,

The 5 shows a flow chart, by means of which the inventive method will be illustrated in more detail. For each of the injectors of the injection system, which are only schematically indicated here, a collective pressure wave correction is initially carried out in a manner known per se 500 , This collective pressure wave correction provides for assumed assumed with respect to a pressure wave centrally controlled injectors a first (collective) correction function f _K , which depends essentially on the parameters injection mass Δm_Einspr and Ansteuerdauer .DELTA.t. This correction function is still normalized according to an embodiment for the subsequent further processing to the mean value of the injection quantity m_mit 505 which corresponds to the value not influenced by the pressure wave. The normalized correction function f _K , norm is buffered in the form of a correction matrix in a control unit of the internal combustion engine 510 ,

In step 515 Injector-specific parameters are recorded. Here, either in a conventional manner, an actual quantity comparison is performed and the resulting data taken as Ken sizes. Alternatively, the individual control data of the injectors, the ratio A / Z (drain / inlet throttle) of the respective injector or the opening pressure p_Opening of an injection nozzle of the respective injector are used as such characteristic. The determined raw data of the individual injector parameters are then normalized to the already mentioned mean value m_mit 520 and transmitted in the form of a control code to said control unit 525 and there also cached. The values of the normalized correction function buffered there are preferably amplitude-modulated or amplitude-scaled by means of the detected individual injector parameters. It goes without saying, however, that the correction function can also be changed in another way by means of the cited parameters, for example by weighted scaling or the like.

From the transmitted data of the normalized injector parameter, a fixed or variable scaling factor is calculated in the controller 530 and rescaling the normalized correction function f _K , norm for each individual injector by means of the scaling factor 535 , from which a new correction function F _K , norm, inj.-indiv. results. Finally, using the new correction function F _K , norm, inj. Indiv. the already described actual pressure wave correction of the control data of the individual injectors made 540 ,

The The above-described method can be either in the form of a circuit in a specially designed control unit or implemented in the form of a control code in the engine control unit itself. Such a device has control or computing means, by means of first of all a pre-described collective pressure wave correction for the injection elements carried out and from said first correction function is determined. By suitable storage means becomes the first correction function buffered in the form of a correction matrix in said control unit. Furthermore, sensor means for detecting individual characteristics of the Injection provided. Alternatively, these characteristics of the engine control unit supplied, provided the described actual quantity adjustment is taken as a basis. Next are computational or control means to the above Conversion of the first correction function provided by means of the detected characteristics. The device finally includes Arithmetic or control means, by means of which a current amount of fuel to be injected correcting control signal of the injectors accordingly becomes.

Claims (11)

Method for controlling a Einspritzsys having at least two injection elements Tems an internal combustion engine, wherein a fuel metering is divided into a first partial injection and at least a second partial injection and wherein a determined by means of the at least two injectors fuel quantity determining control signal in response to a pressure wave influencing the at least two partial injections is corrected, characterized in that for at least a collective pressure wave correction is performed and a first correction function is determined that individual characteristics of the at least two injection elements are detected and that the first correction function is converted by means of the detected individual characteristics of the at least two injection elements in a second correction function, by means of which the control of at least two injection elements is pressure wave corrected. Method according to claim 1, characterized in that that the conversion of the first correction function by means of the detected individual characteristics of the at least two injection elements in the second correction function by amplitude scaling or amplitude modulation of the first Correction function is performed. Method according to claim 1 or 2, characterized that the individual characteristics of the at least two injection elements of one for the at least two injection elements each carried out Actual quantity adjustment to be formed. Method according to one of the preceding claims, characterized characterized in that the individual characteristics of the at least two injection elements through the relationship a drain / inlet throttle of the respective injection element and / or by the opening pressure an injection valve of the respective injection element formed become. Method according to one of the preceding claims, characterized in that the first correction function takes the form of a correction matrix in a control unit the internal combustion engine is cached. Method according to one of the preceding claims, characterized characterized in that the determined individual characteristics of the transmit at least two injection elements in the form of a control code to a control unit of the internal combustion engine become. Device for controlling at least two injection elements having injection system of an internal combustion engine, wherein a Fuel metering in a first partial injection and at least a second split injection is split and wherein means are provided are, by means of which a the amount of fuel to be injected determining control signal dependent on from a pressure wave influencing the at least two partial injections is corrected, characterized by means for performing a collective pressure wave correction for the at least two injection elements and for determining a first correction function, by means for detecting individual characteristics of the at least two injection elements and by means for converting the first correction function by means of the detected individual characteristics of the at least two injection elements in a second correction function, by means of which the control of at least two injection elements is pressure wave corrected. Device according to claim 7, characterized in that in that the means for converting the first correction function is a Amplitude scaling or amplitude modulation of the first correction function cause. Apparatus according to claim 7 or 8, characterized that the means for recording individual characteristics of the at least two injection elements with means for performing a Actual quantity adjustment for the at least two injection elements work together. Apparatus according to claim 7 or 8, characterized that the means for recording individual characteristics of the at least two injection elements cooperate with means which the ratio a drain / inlet throttle of the respective injection element and / or the opening pressure provide an injection valve of the respective injection element. Device according to one of claims 7 to 10, characterized by means for buffering the first correction function in the form of a correction matrix in a control unit of the internal combustion engine.