EP1716331B1 - Method for synchronizing cylinders in terms of quantities of fuel injection in a heat engine - Google Patents

Description

The invention relates to a method for equalizing the differences in the injection quantity between the cylinders of an internal combustion engine, in which the injection quantity differences, which are present at an operating point in the lower speed range at the applicable there in regular driving injection parameter values by means of a cylinder-specific measurement method for detecting the rough running of the internal combustion engine determined and assigned to the low operating point, and in which for operating areas with higher loads and speeds for a selected injection parameter, an adaptation of the injection quantity differences is performed.

Such a method is already out of the DE 197 00 711 A1 known.

In a multi-cylinder internal combustion engine results in the injection of fuel into the combustion chambers by scattering in particular the mechanical properties of the injection device, such as the injectors for diesel engines with common rail, a systematic error. Due to manufacturing tolerances of said components and different wear (aging phenomena) different fuel quantities of the combustion in the individual cylinders are supplied with the same injection period and otherwise identical boundary conditions. The different fuel quantities lead to a different power output of the individual cylinders, which in addition to a Increase in rough running also leads to an increase in the amount of harmful exhaust gas components.

It is known to evaluate the rough running of an internal combustion engine in order to draw conclusions about the injection quantity in the various combustion chambers. For this purpose, z. B. measured with a speed sensor, the rotational acceleration of the crankshaft, wherein the rotational acceleration depends on the respective injection quantity. Thus, a large injection quantity in the affected combustion cycle causes a correspondingly large rotational acceleration of the crankshaft, whereas a small injection quantity only leads to a correspondingly smaller rotational acceleration. This uneven running is counteracted in known internal combustion engines in that the injection quantities in the individual combustion chambers are matched by a suitable control of the various injectors to each other. The control signals for the various injectors are in this case changed until all cylinders make the same contribution to the torque, which suggests a uniform injection quantity in the various combustion chambers.

This known anti-jerk control for cylinder equalization with respect to the injection quantities is limited in application to low load points under stationary operating conditions, for example idling. Deceleration or acceleration, as typically occurs in higher operating ranges, could be misinterpreted by the crankshaft speed sensor as an injection quantity differential.

However, limiting to a low operating point to determine the injection quantity differences is problematic, since these with at least one of the injection parameters, z. As injection pressure and injection time, vary. Accordingly, the injection quantity differences determined at a low operating point can not be used for equality in the entire operating range, eg. B. can be used as the global correction factors for a control parameter of the injectors, but must be adapted to the applicable at higher operating points injection parameters, but this is not readily possible because of the mentioned condition of steady-state operating conditions for the smooth running control.

In the above DE 197 00 711 A1 in which the injection period is subjected to cylinder-specific correction factors for cylinder equalization with respect to the injection quantity, it is proposed to adapt the correction factors determined at a low operating point to higher operating ranges by an adaptation factor f (p, t) dependent on the injection parameters pressure and injection time duration. The values of this adaptation factor are to be stored in a characteristic map and taken from this for adapting the correction factors during driving operation. Although the known method avoids an adaptation under transient operating conditions, but only with the aid of a predetermined characteristic map whose values can not optimally meet the real present, with the life of the vehicle variable dependency ratios of the injection quantity differences.

A similar method, in which the correction amounts are detected at an operating point for an injection parameter value and then transferred to the other operating points by calculation, is known from US Pat US 4,667,634A known. From the DE 198 55 939 A1 is also a method for cylinder equalization in which the adaptation values for the injection quantities are detected at an operating point for an injection parameter value and then adopted for all values of the injection parameter in the entire operating range. Finally, out of the DE 100 12 025 A1 a method for cylinder equalization, in which the necessary injection correction factors are determined and stored in several operating points. The cylinder equalization is carried out by means of a controller, the controller interventions directly correspond to the injection correction factors, the adaptation then takes place when the respective operating points in the regular operation, ie not in a special diagnostic cycle, actually achieved.

The invention is based on the object to provide a method of the type mentioned, which allows to determine the actual, injection-parameter-dependent systematic error with respect to the injection quantities with respect to a cylinder equalization in a simple manner.

This object is achieved by the features of claim 1. The dependent claims relate to advantageous developments and refinements of the invention.

According to the invention, in a generic method in the low operating point, the selected injection parameter is set for adaptation to a value which deviates from the value applicable there in normal driving operation. Under the regular driving operation, it is understood that e.g. at low loads corresponding low injection pressures. On the other hand, the regular driving operation is deviated, if e.g. at low loads high injection pressures. Then, for this set injection parameter value, the injection quantity differences can be determined by means of the measurement of the rough running and learned as adaptation values assigned to the respective injection parameter value. During this adaptation, care must be taken to limit the dynamics of the operating point which is variable with the respectively set injection parameter value, since a changed injection parameter value would otherwise result in deceleration or acceleration not initiated by the driver of the vehicle, at least in a new operating point, ie non-stationary conditions during the adaptation, would say.

Particularly preferred is an embodiment of the method in which at least one second injection parameter is set such that the operating point remains at least approximately stationary in order to limit the dynamics of the low operating point during the adaptation. This can advantageously be achieved by adapting to successively higher values of the injection parameter selected injection pressure to limit the dynamics of the low operating point in each case a correspondingly shorter injection period is set. The second or further injection parameters are thus controlled here as auxiliary quantities such that the driver does not notice anything of the adaptation process. Since a few piston strokes are sufficient for adaptation, the engine control can easily be adjusted so that the driver can not cancel the stationary conditions during the critical adaptation phase, or only when exceeding a threshold in the desired performance requested by the driver via the gas.

In all embodiments of the method according to the invention there is the advantage that a low operating point can be selected for the adaptation, in which the highest sensitivity and / or reliability of the measurement of rough running is achieved, although a correct adaptation for high operating ranges is made. In particular, the low operating point in the idling range can be selected.

The learned adaptation values are used to calculate cylinder-specific correction factors with which, as a rule in the context of the smooth running control during the adaptation process and while driving, a control parameter of an injection device of the internal combustion engine is applied such that an equalization of the injection quantities takes place.

It has proved to be advantageous that the injection device for each cylinder is formed by an injector with a piezoelectric actuator, wherein the drive energy of the actuators is used as a driving parameter. It can therefore in particular for different values of the injection pressure an adaptation of the actuator stroke necessary for equality is carried out.

To detect the uneven running of the internal combustion engine, the rotational acceleration of the crankshaft of the internal combustion engine caused by the cylinder-specific different injection quantities can be evaluated. The determination of the adapted injection quantity differences or the adapted correction factors for equality can thus be based on a very accurate measurement methodology.

The inventive method also opens up the possibility that the absolute value of the associated injection quantity is determined at the stationary operating point set for adaptation with equivalent injection quantities from a stored torque model of the internal combustion engine. A diagnosis of the absolute value of the injection quantity is just for the diagnosis of small injection quantities, in particular of pre-injection amounts that are in the range of a few milligrams, crucial for compliance with the limits of exhaust emissions.

Figur 1

ein Flussdiagramm zur Durchführung der erfindungsgemäßen Einspritzmengengleichstellung,

Figur 2

ein Flussdiagramm zur Durchführung der bevorzugten Einspritzmengengleichstellung mittels Ladungszeitadaption.

The invention will be explained in more detail below with reference to the schematic drawing. Show it:

FIG. 1

a flow chart for performing the injection quantity equalization according to the invention,

FIG. 2

a flowchart for performing the preferred injection quantity equalization by means of charge time adaptation.

After start 1 of the injection quantity equalization, an initialization phase 2 is provided in the next step, in which the adaptation values stored in an earlier diagnostic cycle are loaded into an engine control unit (not shown). The initialization of a new diagnostic cycle can be done both after each startup of the internal combustion engine, as well as after certain, specifiable time or maintenance intervals.

After the end of the initialization 2, the activation conditions are checked in a passive diagnostic step 3. The aim is to wait until the preferred operating conditions for adaptation to a regular or deviating injection parameter value have been reached. These include, for example, the load, the speed or the coolant temperature. If necessary, the motor control must be changed so that in the subsequent adaptation, the dynamics of the temporal change of the selected for performing the adaptation cycle operating point is limited.

As soon as the activation conditions are fulfilled, the actual, active diagnostic cycle 4 is started. With the regular injection parameters 5 associated with the engine operating state (see injection parameter set in FIG FIG. 1 ) First, a rough running control 6 is performed. As a result, the injection quantities of the individual injectors of the internal combustion engine are matched to one another in the preferred, low operating point. On the other hand, at this point in the process, there is also the additional evaluation possibility that at the preferred, low operating point with the predetermined regular injection parameter values, an injection quantity known from the torque model is concluded, which must be given in accordance with the achieved torque.

Thereafter, in step 7 (adaptation of the activation parameters), further injection parameters or injection parameter sets i are loaded and the uneven-running control is carried out with a determination of the injection quantity differences present at the set value of the selected injection parameter or with the equality by corresponding correction factors for a control parameter. For adaptation, a suitable drive parameter, such as, for example, the energy supplied to the actuators, is selected. The resulting adaptation values are added to the injection parameter set, ie primarily the injection parameters, such as the injection parameters. Injection pressure and injection period whose influence on the injection quantity differences to be recorded, assigned and stored so that they can be retrieved later, when driving with higher loads and speeds and the associated regular values of the selected injection parameter for direct injection amount equalization without diagnostic cycle. If the adaptation has been carried out for a sufficient number of interpolation points (typically five to ten), ie, for example, for all of the injection parameter values of the pressure set i = 1 to i = k, the end 8 of the adaptation or of the current diagnostic cycle is reached and the stored adaptation values can be obtained in Driving operation for equality of injection quantities can be used.

It has been found that the different injection quantities of injectors, which depend on the injection duration, can be easily adjusted to one another in such a way that the stroke of the actuators is changed. This means, for example, that an adaptation of the actuator stroke is carried out for different injection pressures selected as injection parameter values. On the other hand, as the injector control variable Of course, the drive energy used can also be used to vary the start of injection.

During each diagnostic cycle, the last stored adaptation values or correction factors are overwritten by the newly determined, whereby in particular the aging phenomena of the injection device which have occurred in the meantime and which possibly lead to changed variations with regard to the injection quantities into the different combustion chambers are taken into account.

This in FIG. 2 The illustrated method performs an initialization in step 11. The stored adaptation values are loaded. In step 12 it is checked whether the activation conditions are fulfilled. This means to understand whether constant operating conditions are present, such as constant load, constant speed, constant temperature of the coolant, etc. Thus, as shown in step 13, the diagnosis remains passive until the activation conditions are met in step 12. Then, in step 14, continue by loading the injection parameters for an initial charge / discharge time. For example, the initial charge / discharge time can be set to 200 μs. The injection parameters include the injection pressure, injector energy, type of injection, which means whether it is a pre-, main-, post-injection. Once these parameters have been loaded, the procedure is continued in step 15. The running disturbance regulation takes place cylinder-selectively, ie that for example for a four-cylinder engine first the cylinder Nr.1 is regulated. If the injection parameters for the injector of cylinder No. 1 are set, the injector of the second cylinder follows. The regulation may include the charge / discharge time, the injection pressure, the drive energy, and set the type of injection. In particular, the control can be performed at a defined (fixed) control duration (injection period) and defined (fixed) injection pressure, wherein the actuator energy is adjusted accordingly. With a rail pressure of, for example, 1500 bar and an injection quantity of 0.84 mg, activation times of less than 160 μs must be realized.

In step 16 it is checked whether with these variables the rough running is below a threshold value S. If this is not the case, then in step 17, the activation duration must also be changed. This is particularly necessary for "bad" manufactured injectors that poor or not cope with these short load / unload times. In such injectors and short discharge times, the amount of fuel injected is independent of the actuator energy. It sets up a kind of "quantity saturation" and the injection quantity can not be changed by increasing the actuator energy. This means that an injection adaptation in a defined operating state does not have to be carried out solely by energy adaptation, but by means of an extension of the activation duration, which thus extends the injection duration.

As a result of a successful cessation of exercise after step 16, the injection rates of the individual injectors are aligned. These injection parameters are stored for the associated charge / discharge time τ _i (step 18). In step 19, it is checked whether the charge / discharge time τ _{i is} greater than or equal to an extreme value. Here, the extreme value is for example 140 μs. In the above example, the initial value τ ₀ is 200 μs. It should be noted that the index i here is equal to zero. Since the condition established in step 19 is not satisfied, it continues in step 20. Before loading the next parameter set in step 14, the loading / unloading time is previously reduced by 10 μs in step 20. Thus, the charge / discharge time τ _{1 is} equal to 190 μs. In step 21, only the index is incremented by one. The existing injection parameters for τ ₁ are now loaded in step 14. As already described above, steps 15 to 19 follow. If all parameter sets are adjusted for the different charge / discharge times, the constant injection pressure (eg 1500 bar) can be set to a new other constant injection pressure (eg 1400 bar). As soon as the new pressure is applied in step 12, the actuator energy is determined according to steps 14 to 19 for each charge / discharge time of 200 to 140 μs. This can be done for different pressures. As soon as a sufficient number of measured values are available, the method ends in step 22. It should be noted that the step-by-step change of the charging / discharging time by 10 μs in step 20 has been given by way of example only. For a finer modeling, differences from one charge / discharge time to the next charge / discharge time of 1 μs are conceivable. This diagnosis according to the invention can be carried out very quickly, since only a few piston strokes are sufficient.

In summary, the method according to the invention makes it possible to diagnose the injection quantity differences or the injection quantity itself at a preferred, low operating point at which the highest sensitivity and reliability of the rough-running control exists. At this operating point, the diagnosis and adaptation then also take place for injection parameter values which apply to other operating points during driving operation. It is done at the low operating point so both a compensation of the injection quantity differences between the individual injectors as well as a calibration of the injection quantity to the associated, in the diagnostic cycle artificially set values of the selected injection parameter, wherein an undesirable movement of the adaptation operating point by the opposite setting of other injection parameter values is prevented or limited. Preferably, an injection quantity equalization by energy control of the injector drive parameter is dependent on, in particular, the injection parameter pressure.

Optionally, it is possible at the adjusted operating point on the basis of knowledge of the engine operating state (temperature of coolant, active consumers) to read the absolute value of the injection quantity from the torque model and to use it for the exact calibration of the injection quantity / injection duration map.

Claims (13)

1. Method for synchronising, between the cylinders of an internal combustion engine, the differences in the quantity of fuel injected, in which the differences in the quantity of fuel injected which exist at an operating point in the lower engine-speed range with the injection parameter values valid at that point under normal operating conditions are determined by means of a method of measuring individual cylinders to record irregularities in the running of the internal combustion engine and are assigned to the low operating point and in which, for operating ranges with higher loads and engine speeds, an adaptation of the differences in the quantity of fuel injected is carried out for a chosen injection parameter,
   characterised in that
   at the low operating point the chosen injection parameter is set for adaptation (4, 5, 6, 7) to different values which deviate from the value applicable at that point under normal operating conditions, and in that for the set values the differences in the quantity of fuel injected are determined in each instance by means of measurement of the irregularities in the running of the engine and are learned as adaptation values which are assigned to the respective injection parameter value, wherein during the adaptation (4, 5, 6, 7) the movement of the operating point, which changes with the injection parameter value set in each case, is limited.
2. Method according to claim 1,
   characterised in that, in order to limit the movement of the low operating point during adaptation (4, 5, 6, 7), at least one second injection parameter is set such that the operating point remains at least approximately stationary.
3. Method according to claim 2,
   characterised in that, in the process of adaptation (4, 5, 6, 7) to successively higher values of the injection pressure chosen as an injection parameter, a correspondingly shorter injection period is set in order to limit the movement of the low operating point.
4. Method according to claim 2,
   characterised in that, in the process of adaptation (4, 5, 6, 7) to successively lower values of the injection pressure chosen as an injection parameter, a correspondingly longer injection period is set in order to limit the movement of the low operating point.
5. Method according to any one of claims 2 or 3, characterised in that the injection pressure is changed gradually by a defined amount.
6. Method according to any one of the preceding claims,
   characterised in that for the adaptation (4, 5, 6, 7) a low operating point is selected at which the maximum sensitivity and/or reliability of measurement of the irregularity in the running of the engine is achieved.
7. Method according to any one of the preceding claims,
   characterised in that the low operating point is chosen in the idling range.
8. Method according to any one of the preceding claims,
   characterised in that the learned adaptation values serve to calculate cylinder-specific correction factors, which are applied to an activation parameter of an injection device of the internal combustion engine such that a synchronisation of the quantities of fuel injected occurs.
9. Method according to claim 8,
   characterised in that the injection device for each cylinder is formed by an injector with a piezoelectric actuator, wherein the activation energy of the actuators is used as an activation parameter.
10. Method according to claim 9,
    characterised in that, for a defined loading/unloading time of the injector, the actuator energy is adapted correspondingly.
11. Method according to claim 10,
    characterised in that the loading/unloading time of the main injection is set to an initial value (τ₀) and is gradually changed to an extreme value, wherein with each step the actuator energy is adapted correspondingly.
12. Method according to any one of the preceding claims,
    characterised in that, in order to record the irregularity in the running of the internal combustion engine, the angular acceleration of the crankshaft of the internal combustion engine caused by the differing quantities of fuel injected in individual cylinders is analysed.
13. Method according to claim 12,
    characterised in that, at the stationary operating point set for adaptation (4, 5, 6, 7) with synchronised quantities of fuel injected, the absolute value of the associated quantity of fuel injected is determined from a stored model of the torque of the internal combustion engine.

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