SE535076C2 - Method and apparatus for fuel adaptation or determination of fuel composition in an internal combustion engine - Google Patents

Abstract

The invention relates to a method and a device for operating an internal combustion engine with at least two cylinders which can be operated with fuel stored in a tank of varying fuel quality and / or stored fuel mixtures from a first and at least one second fuel in different mixing ratios and wherein different fuel qualities and / or fuel mixtures composition requires different air / fuel conditions to achieve a stable combustion and / or has different evaporation behaviors. According to the invention, it is provided that in a post-start phase of the internal combustion engine a cylinder individual variation of the fuel quantity is carried out at at least one first cylinder which is supplied to the cylinder towards a leaner or fatter air / fuel mixture and at least a second cylinder a corresponding variation is made towards a fatter or leaner air. / / fuel mixture and in connection therewith a difference of the running unevenness of both cylinders is evaluated, the influence of the variation on the difference of the running unevenness of both cylinders being evaluated and a fuel adaptation being carried out therefrom for all cylinders or the fuel composition being determined. (Figure)

Description

The arbitrary mixture of petrol and alcohol results in a wide range of variations of the fuel properties, especially of the stoichiometry and the evaporation properties.

DE 4117440 C2 discloses a method for adaptive setting of a fuel / air-fuel mixture for taking into account fuel properties during operation of an internal combustion engine which has a lambda control which produces a control factor RF and which has an adaptation integrator which produces an adaptation factor AF. with variable adaptation rate, which in addition to the control factor RF affects the setting of the fuel-air mixture.

This ensures that it is checked whether the lambda control wind amplitude exceeds a first threshold value and if so, the adaptation rate is set at an increased value until a predetermined condition is met, after which feedback is returned to a low adaptation rate.

The method makes it possible to drive combustion engines that can be operated with different fuels without disturbance. For example, in the case of a change of a petrol fuel to a fuel mixture of 85% ethanol and 15% petrol, the injection time must be extended by more than 20%, in order to obtain the same lambda value in the exhaust gas. According to the method described in the document DE 4117440 C2, a corresponding adaptation procedure is performed in addition.

Since in the case of a fuel change, in comparison with the equalization of the aging effect or the manufacturing effect, a strong correction of the injection times must be made and thus of the adaptation procedure the adaptation speed is significantly increased in the proposed process at an identified fuel change.

On the basis of the set adaptation value, the fuel-mixture ratio can be determined. Despite the increased adaptation rate, the process requires a sufficiently long turn-in time. If a strong change in the fuel-mixing ratio is caused by a refueling lead, this can lead to starting difficulties and to the ignition failing ("coughing"), which leads to increased exhaust emissions.

In addition to a change in the fuel-mixing ratio of an internal combustion engine running in Flex-Fuel operation, a variation in the fuel quality, for example even in pure petrol operation, can also lead to starting problems. In this case, the fuel quality is especially included in the fuel's regeneration properties. If the alcohol content is unknown, a distinction between the two causes is difficult. A constitution of the air / fuel mixture in response to poor starting behavior of the internal combustion engine is therefore not always suitable for Flex-Fuel use, as is known from pure petrol operation.

In another application from the applicant with file number DE 10 2007 035317 a method is known for operating an internal combustion engine with at least two cylinders which can be propelled with fuel stored in a tank of varying fuel quality and / or stored fuel mixtures from a first and at least one second fuel in different mixing ratios and wherein different fuel grades and / or fuel mixtures require different air / fuel ratios to achieve a stable combustion and / or exhibit a varying evaporation behavior. It is ensured that, in the case of at least one cylinder, a cylinder-individual variation of the fuel mixture supplied to the cylinder is carried out against a leaner and / or against a fatter air-fuel mixture, that the influence of the variation on the starting properties and / or the smoothness of the cylinder and / or internal combustion engine is evaluated. that when an improvement of the starting properties and / or smoothness is achieved, a fuel slide adaptation is carried out for all cylinders.

The process enables rapid identification and avoidance of starting problems in the event of a change in fuel quality or fuel composition with an effect on the flammability of the fuel mixture.

When using the procedure, however, it turns out that in practice problems can arise in an evaluation of the thread uniformity, which can lead to an incorrect interpretation of the thread uniformity values. On the one hand, therefore, very stable boundary conditions are required with respect to, for example, speed, load and / or temperature, which in practice cannot always be guaranteed. On the other hand, spreads, which can be traced back to manufacturing tolerances and / or aging of components, can distort the evaluation.

It is therefore the task of the invention to provide a method for providing an optimal air / fuel mixture especially for the post-start phase of an internal combustion engine in which a reliable evaluation of the running speed is guaranteed.

It is further the task of the invention to provide a device for carrying out the procedure. 10 15 20 25 30 535 C175 Description of the invention The object concerning the process is solved according to the invention by carrying out at least a first cylinder a cylinder-individual variation of the fuel mixture which is supplied to the cylinder against a leaner or against a fatter mixture of air / fuel at at least a first cylinder. in the case of at least one second cylinder, a corresponding variation is carried out against a fatter or a leaner air / fuel mixture and from this a fuel adaptation is carried out for all cylinders or the fuel composition is determined, in connection with the variation of the air / fuel mixture in the first and the second cylinder, a difference between the gait uniformity of the two cylinders is evaluated, whereby the input of the variation on the difference between the gait uniformity of the two cylinders is evaluated and that a fuel adaptation is performed for all cylinders or that the fuel composition is determined therefrom.

The task of the device is solved by the combustion engine having a control-1 evaluation unit, with which a cylinder-individual variation of the amount of fuel supplied to the cylinders can be given (controlled) against a leaner or against a fatter air / fuel mixture and with which a fuel adaptation can be performed for all cylinders. or the fuel composition can be determined, the control / evaluation unit being designed in such a way that a difference between the smoothness of the cylinders which are involved in the mixture variation can be evaluated.

With the inventive method and the device for carrying out the process, an optimal air / fuel mixture can be specified, especially in the post-start phase, before a reliable feedback from the Iambda probe is available in this phase, whereby it can be reliably and accurately identified if the mixture is too lean. or too fat. This applies to petrol-powered internal combustion engines as well as to Flex-Fuel applications, as described earlier. Accordingly, it is assumed that differences in gait uniformity values or gait uniformity care between at least two different cylinders are used and not absolute gait uniformity values. Thus, the above-mentioned disadvantages regarding unstable boundary conditions resp. spreads are largely eliminated. A further advantage results from the fact that when evaluating the difference of the smoothness or the smoothness from only two cylinders, a clearer and above all earlier feedback to the mixture can be derived than would be possible in an evaluation of the total smoothness. ten.

In a preferred method variant, it is provided that the cylinder-individual variation of the air / fuel mixture of the first cylinder and of the second cylinder is carried out at a constant target lambda value taken together for both cylinders. The target lamb care can then be time-dependent, depending on the load and operating phase.

The variation of the air / fuel mixture of the first cylinder and the second cylinder can then be carried out continuously or also periodically, typically a variation of up to about 10% is disturbed against the average value of the air / fuel mixture of the first cylinder and the second cylinder. . In addition, the variation of the air-I fuel mixture can also be switched between both cylinders, whereby the hitherto grease-driven cylinder becomes a lean-driven cylinder and the hitherto lean-driven cylinder becomes a grease-driven cylinder. This has the advantage that cylinder individual differences (different adjustment) can be filtered out. In a further method variant, it may be provided that the cylinder-individual variation of the air / fuel mixture of the first cylinder is carried out symmetrically with the cylinder-individual variation of the air / fuel mixture of the second cylinder. This offers on the one hand the advantage that through the variation the lambda value remains constant for the total combustion engine. On the other hand, the variation of the air / fuel mixture can easily be given control-technically by switching characters for the two partial cylinders. In an alternative method variant, while maintaining the principle for evaluating the difference of the walking smoothness, it can be provided that the cylinder-individual variation of the air / fuel mixture of the first cylinder is carried out by means of a cylinder-individual variation of the air / fuel mixture of your second cylinders of combustion engines. , whereby for all participating cylinders taken together a constant target lambda value is set.

It is also conceivable that the cylinder-individual variation of the air-mixture mixture is carried out at your cylinder pairs, whereby for all participating cylinder pairs taken together a constant target lambda value is set. Here, too, the maintenance of the evaluation principle with respect to the difference of the walking smoothness is taken care of for the participating cylinder pairs.

In carrying out the method variant, it has proved advantageous when the value k = 1 is set as the target lambda value. This is derived from the course of the walking smoothness depending on the lambda value. The curve is similar to a "bathtub" and has a pronounced rise at a value from k = 1. The walking unevenness increases rapidly for a value k> 1. In general, therefore, the cylinders are driven around a value k = 1, a cylinder being driven at a value k> 1 and the second involved cylinder at k <1, which is very easy to realize and also relatively insensitive with respect to magnitudes of the smoothness.

The evaluation procedure further ensures that the walking evenness difference is compared with a predetermined threshold value resp. with a setpoint for the gait evenness difference and depending on the result of the comparison, the total mixture is made leaner or fatter, with which a simple and robust adjustment of the mixture preparation can be realized. In addition, a corresponding control circuit, for example in the form of a P1 control, is provided which is correspondingly realized technically in the device or realized with a corresponding software.

It can then be provided that a value for the smoothness of the grease driven cylinder / the grease driven cylinders is subtracted from the value of the walking smoothness of the lean driven cylinder / cylinders and is compared with the threshold value and if this threshold value is exceeded the total mixture is made fatter and if the threshold value is exceeded, the total mixture is made leaner. This evaluation can be realized in a short time within the control / evaluation unit without large consumption of hardware and / or software. It is used here that a forecast of the current lambda value is possible due to the course of the gait uniformity in dependence on the lambda value and the previously determined difference for the gait uniformity of the cylinders and correspondingly a mixing operation can be performed. If the threshold value is not exceeded and the negated threshold value is not exceeded, it can be assumed that the current lambda value is in the vicinity of the target lambda value, usually k = 1. 10 15 20 25 30 535 075 The functionality of the method with the previously described the process variants can be implemented in the control / evaluation unit or in a superior engine control device of the internal combustion engine as hardware and / or software. A software implementation has the advantage that the parameters can be changed quickly through a software update if new knowledge is available.

A preferred use of the process as previously described provides for the adaptation of operating parameters of an internal combustion engine to the composition of a gasoline / ethanol fuel mixture and / or a gasoline / methanol fuel mixture and / or gasoline / ethanol / methanol fuel mixture and / or a diesel. / biodiesel fuel blending. Especially in Flex-Fuel applications, this method can be used to determine the ethanol content of the petrol. The method can also be used to advantage for plausibility (reasonableness assessment) of an ethanol sensor. The method can also be used in a system without a sensor, which takes place, for example, in an ethanol content determination with the aid of a start / water flow adaptation. It is used here that the gait unevenness, especially in the post-start phase, depends very strongly on the ethanol content resp. the methanol content of the fuel mixture due to the specific evaporation properties. This makes it possible, among other things, to distinguish ethanol content errors from the usual multiplicative fuel errors.

An equally preferred use of the method provides for the adaptation of operating parameters of the internal combustion engine to a present gasoline grade.

The invention is explained in more detail below with the aid of an exemplary embodiment illustrated in the figures. It shows: Fig. 1 in schematic illustration a fl fate diagram for the process and Fig. 2 in schematic illustration a diagram for gait roughness depending on a lambda value or an ethanol content.

Fig. 1 shows a fate diagram 1 for the inventive procedure. After a start 10 of the procedure, it is next checked in a reading 20 for the connection conditions, if all connection conditions are met. These can be, for example, fixed waiting times between periodically carried out mixing operations or operating parameters, with which a conclusion can be drawn about a disturbance-free operation of the internal combustion engine. If the reading conditions are not met, a repeat is performed until all conditions are met. It may also be ensured that the procedure is stopped further. If all the conditions are met, in a function block, the thinning / greasing 30 takes place in a targeted thinning of the air / fuel mixture for a first cylinder of the internal combustion engine. A second cylinder is offered in the assumed example a greased air / fuel mixture, whereby powering and constitution of the air / fuel mixture for both cylinders of the internal combustion engine shall be carried out symmetrically in the assumed process example. Preferably, a value of x = 1 is maintained over all cylinders.

The connection is determined in a smoothness evaluation block 40 by a difference of the roughness roughness between the two cylinders participating in the process. Thereby, the difference of the gait uniformity is formed by subtracting a value for the gait uniformity of a cylinder operated with a lean air / fuel mixture from a value of the gait uniformity of a cylinder driven with a pre-greased air / fuel mixture. The smoothness difference (AL) formed in this way is first compared in a reading block 50 with a threshold value (S). If the threshold value (S) is exceeded, which is checked with a reading 51, the total mixture is greased (mixture greasing 60). If the ignored threshold value (-S) is exceeded, which is checked with a reading 52, the total mixture is emaciated (emaciated) (mixture emaciation 70). If the threshold value (S) at reading 51 is not exceeded and the negated threshold value (-S) is not exceeded at reading 52, it can be assumed that a lambda value 112 is in the vicinity of A = 1. In this case there is no total mixture fattening or total mixture emaciation. regression takes place at the beginning of the procedure and the steps after reading 20 are repeated or the process is stopped, for example if a time lapse is determined. In a further reading 80, it can be arranged that with the aid of this reading it is checked whether a period end has been reached. This reading is especially necessary in a periodic use of the method. If this is not the case, the difference of the smoothness is further determined in the smoothness evaluation block 40 and corresponding to the comparison with the threshold value (reading block 50), the total mixture is fattened or emaciated (mixture greasing 60 or mixture emaciation 70). If the end of the period has been reached, a further reading 90 is performed to check whether the end condition has been reached. This can, for example, be the case when the lambda control is active in the after-start phase of the internal combustion engine resp. fully delivers reliable values from the lambda probe. If this is the case, the procedure is stopped (end 100). If this is not the case, the system performs a renewed passage of the process step beginning with reading 20.

In Fig. 2, a diagram 110 is illustrated for the course of a value of the walking smoothness 11 1 in dependence on a lambda value 112. The 'bathtub-like' can / course has a strong increase at an x = 1. At small lambda values 112, considerably below k = 1, the walking unevenness 111 also increases very strongly. Ideally, the differential smoothness 116 is relatively low at a target lambda value 113 (here k = 1), since the smoothness of the cylindrically driven cylinder 111 and the corresponding fat-driven cylinder 118 differs only slightly in this curve section. A total lambda value 119 for the two cylinders involved in the mixing variation corresponds to the target lambda value 113 (rake = 1).

If a large differential uniformity is detected in the case of too lean mixture 114, an engagement of grease mixture 120 takes place. ensure that the walking uniformity 111 is evaluated in dependence on an ethanol content 140 instead of the lambda value 112.

With the method and the device for carrying out the method, an optimal mixture can be set in the post-start phase, whereby a reliable and robust evaluation of the gait unevenness is applied.

Claims (12)

10 15 20 25 30 535 076 10 Patent claims Method for operating an internal combustion engine with at least two cylinders that can be operated with fuel stored in a tank of varying fuel quality and / or stored fuel mixtures from a first and at least a second fuel in different mixing ratios and wherein different fuel grades and / or fuel mixtures of different composition requires different air / fuel conditions to achieve a stable combustion and / or exhibits a varying evaporation behavior, whereby in a post-start phase of the combustion engine a cylinder-individual variation of the amount of fuel supplied to a cylinder is carried out at at least a first cylinder or against a leaner a fatter lu fi / fuel mixture and in the case of at least one second cylinder a corresponding variation is carried out against a fatter or leaner air / fuel mixture and from this a fuel adaptation is carried out for all cylinders or the fuel composition is determined characterized in connection with the variation of air / fuel the landing in the first and the second cylinder, a difference between the smoothness of the two cylinders is evaluated, whereby the variation in the difference in the difference between the smoothness of both cylinders is evaluated and a fuel adaptation is performed for all cylinders or the fuel composition is determined. Method according to Claim 1, characterized in that the cylinder-individual variation of the air / fuel mixture of the first cylinder and the second cylinder is carried out at a constant target lambda value (113) taken together for both cylinders. Method according to claim 1 or 2, characterized in that the cylinder-individual variation of the air / fuel mixture of the first cylinder is performed symmetrically to the cylinder-individual variation of the air / fuel mixture of the second cylinder. Method according to claim 1 or 2, characterized in that the cylinder-individual variation of the air / fuel mixture of the first cylinder is carried out by means of a cylinder-individual variation of the air / fuel mixture of andra your second cylinders of the internal combustion engine, wherein for all participating cylinders taken together, a constant target lambda value (113) is set. 10 15 20 25 30 535 076 ll Method according to Claim 1 or 2, characterized in that the cylinder-individual variation of the air / fuel mixture is carried out at cylinder your cylinder pairs, a constant target lambda value (113) being set for all participating cylinder pairs taken together. Method according to one of Claims 1 to 5, characterized in that the value 7t = 1 is set as the target lambda value (1 13). Method according to one of Claims 1 to 6, characterized in that the difference in gait unevenness is compared with a predetermined threshold value and that, depending on the result of the comparison, the total mixture is made leaner or fatter. Method according to Claim 7, characterized in that a value of the gait uniformity of grease-driven cylinders / of the grease-driven cylinders is subtracted from the value of the gait of a lean-driven cylinder / of the lean-driven cylinders and is compared with the threshold value and if this threshold value is exceeded, the total mixture is made fatter and if the negated threshold value is exceeded, the total mixture is made leaner. Use of the method according to any one of claims 1-8 for adapting operating parameters of an internal combustion engine to the composition of a petrol / ethanol-fuel mixture and / or a petrol / methanol-fuel mixture and / or petrol / ethanol / methanol-fuel mixture and / or a diesel / blood diesel fuel mixture. Use of the method according to any one of claims 1-8 for adapting operating parameters of the internal combustion engine to a present petrol grade. Device for operating an internal combustion engine according to the method according to any one of claims 1-8 with at least two cylinders which can be driven by fuel stored in a tank of varying fuel quality and / or stored fuel mixtures from a first and at least a second fuel in different mixing ratios and wherein different fuel grades and / or fuel mixtures of different composition require different air / fuel conditions to achieve a stable combustion and / or exhibit a varying evaporation behavior, the combustion engine having a control / evaluation unit with which a cylinder individual variation of the amount of fuel supplied to the cylinders can be specified against a leaner or against a fatter air / fuel mixture and a fuel slide adaptation can be performed for all cylinders or the fuel composition can be determined characterized in that the control / evaluation unit is designed in such a way that a difference between the gait uniformity of the cylinders involved v id the mixture variation is evaluated. Device according to claim 11, characterized in that the functionality of the method according to claims 1-8 is implemented in the control / evaluation unit or a superior engine control device of the internal combustion engine.