Method and system for estimating the amount of fuel injected into a spark ignition internal combustion engine

Abstract

A method and a system for estimating the amount of fuel injected into a spark ignition internal combustion engine with which a lambda sensor is associated are described. Based on estimated values over time of a long-term adjustment factor (T) of the amount of fuel delivered by at least one injector apparatus from an amount of air in the combustion mixture estimated by the lambda probe, it is determined whether each of said values is reliable or unreliable as a function of the operating conditions of the engine at which the estimation took place, and the amount (mass) of fuel injected over time is estimated from the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered.

Description

[0001] Method and system for estimating the amount of fuel injected into a spark ignition internal combustion engine

[0002] The present invention concerns in general systems for controlling the propulsion of a vehicle and more specifically a method and system for estimating the amount of fuel injected into a spark ignition internal combustion engine according to the preamble of claim 1 and claim 10.

[0003] The EU Regulation 2017 / 1151 of the European Commission on the approval of motor vehicles has introduced rules regarding emissions from passenger and light commercial vehicles and obtaining information on vehicle repair and maintenance. In particular, a requirement was introduced for newly registered vehicles to be equipped with a system for storing vehicle consumption data. The system, known as OBFCM (On-Board Fuel Consumption Monitoring), defines standardized access to various vehicle operating information, such as fuel consumption, driving speed, etc. This standard allows to verify the real consumption of vehicles over time, without having to resort to sample tests. The data, stored in a control unit, are transmitted to a manufacturer's server on a regular basis, if the vehicle supports communication with the manufacturer and the updating of its systems in OTA mode, or during access to the manufacturer's workshops.

[0004] In general, all vehicles are required to record and report fuel consumption, distance travelled, the flow of fuel to the engine, and the vehicle speed. Fuel consumption is derived from a data indicative of the cumulative amount of injected fuel, and a deviation in consumption equal to 5% of the amount of fuel during the operational life of the vehicle is tolerated (i.e., a difference between actual consumption and estimated consumption equal to ± 5%).

[0005] Any leakage of the vehicle injection system may result in the aforementioned accuracy threshold of the consumption estimate being exceeded with respect to actual consumption.

[0006] It is therefore necessary to be able to accurately determine or estimate the amount of fuel injected during the operational life of the vehicle, as well as to ensure satisfactory accuracy in determining or estimating the amount of fuel injected from the production time of the vehicle throughout its operational life.

[0007] Disadvantageously, in spark ignition internal combustion engines the lambda probe, adapted to detect the presence of oxygen in the exhaust gases to maintain the air / fuel mixture ratio within the optimal efficiency range of the catalytic converter mounted on the vehicle's exhaust system, does not directly detect the amount of fuel injected so that the deviation from the optimal values of the amount of oxygen detected in the exhaust gases cannot necessarily be attributed to an error in the estimation of the amount of fuel injected, but could also be determined by an error in the estimation of the amount of air in the combustion mixture.

[0008] The prior art does not solve the problem of adjusting the estimate of the amount of fuel delivered as a function of the deviation of the behaviour of the injection system from the nominal behaviour if this deviation is greater than 5%, or it makes available complex algorithms for the correction of the deviation in the injection values whose learning time is so high that the deviation cannot be guaranteed to be compensated for by comparison with the conformity test conducted at the time of production of the vehicle, thus not satisfying the requirement that the performance in the accuracy of the estimate of the amount of fuel injected must be maintained in the permissible range from the time of production of the vehicle.

[0009] In light of what is currently known in the art, the present invention aims to provide an efficient and accurate solution for estimating the amount of fuel injected by the injector apparatuses of a vehicle for the detection of the consumption of the amount of fuel during the operational life of the vehicle, in order to ensure the timely calibration of the fuel injector apparatuses for compliance with a predetermined error tolerance threshold on the estimation of consumption, for example a tolerance threshold established by the regulations in force in a predetermined territory. A further object of the invention is to provide an accurate estimate of the amount of fuel injected by the injector apparatuses of a vehicle regardless of the degree of deviation of the behaviour of one or more injector apparatuses with respect to a comparison calibration condition referred to the production time of the vehicle. According to the present invention, this object is achieved thanks to a method for estimating the amount of fuel injected into an internal combustion engine having the characteristics recited in claim 1.

[0010] Particular embodiments are the subject-matter of the dependent claims, the content of which is to be understood as an integral part of the present description.

[0011] A further object of the invention is a system for estimating the amount of fuel injected into an internal combustion engine as claimed.

[0012] In summary, the present invention is based on the recognition that the data acquired by the lambda probe provides an accurate estimate of the deviation of the injected amount of fuel (in the combustion chamber in the case of direct injection or in an intake manifold in the case of indirect injection) with respect to an optimal reference condition in medium-high or high engine load condition where an error in the estimate of the amount of air in the combustion mixture is negligible.

[0013] The method and system for estimating the amount of fuel injected into a spark ignition internal combustion engine, which are the subject-matter of the invention, are therefore based on the selective acquisition of data acquired by the lambda probe and the consequent correction of the estimate of the injected amount of fuel on the basis of the data from the selected lambda probe, the data acquired by the lambda probe being selected under medium- high or high engine load conditions, i.e. medium-high or high torque delivered by the engine, for example a torque greater than 50% of the maximum torque deliverable by the engine.

[0014] Further characteristics and advantages of the invention will be set forth in more detail in the following detailed description of an embodiment thereof, given by way of non-limiting example, with reference to the accompanying drawings, wherein: figure 1 shows a plurality of graphs of errors in estimating the amount of air drawn in, as a function of the amount of air drawn in, for different operating parameters of a spark ignition internal combustion engine of a vehicle as a function of the engine load, according to a first simulation, obtained by injecting a positive error on the aforementioned parameters; figure 2 shows a plurality of graphs of errors in estimating the amount of air drawn in, as a function of the amount of air drawn in, for different operating parameters of a spark ignition internal combustion engine of a vehicle as a function of the engine load, according to a second simulation obtained by injecting a negative error on the aforementioned parameters; figure 3 shows a graph of estimation errors for a selected operating parameter of a spark ignition internal combustion engine of a vehicle as a function of the engine load, according to an experimental test during which a positive and negative error was injected on the pressure measurement signal of the intake manifold; and figure 4 is a block diagram of a system for estimating the amount of fuel injected into a spark ignition internal combustion engine of the invention.

[0015] The assumptions underlying the present invention are shown in figures 1 to 3.

[0016] More specifically, figure 1 shows six graphs indicative of the percentage error in the estimation of the amount of air in the combustion mixture by the electronics associated with the lambda probe in the case of positive variation (simulated error) of different operating parameters of the spark ignition internal combustion engine of a vehicle, in particular from left to right, from top to bottom the pressure trend at the intake manifold, the air temperature at the intake manifold, the relative position of the phase shifter that determines an early opening and / or a delayed closing of the intake and exhaust valves, the position of the exhaust gases recirculation valve (EGR), the temperature of the engine cooling water and the temperature of the exhaust gases brought into recirculation, in all cases depending on the relative load of the engine.

[0017] Each graph shows a cloud of error values associated with the operating parameter in a reference condition (indicated with R) and a cloud of error values associated with the same operating parameter in a condition of simulated variation (deviation) of the parameter (indicated with D), when it has increased by a predetermined simulation amount representative of the consequence of a deviation in the behaviour of the injector apparatus with respect to predetermined initial reference conditions (corresponding to manufacturing setting conditions). Each point of the point cloud is indicative of an engine operating condition, in terms of number of revolutions and relative load.

[0018] Similarly, figure 2 shows six graphs indicative of the percentage error in the estimation of the amount of air in the combustion mixture by the electronics associated with the lambda probe in the case of negative variation (simulated error) of the same operating parameters of the spark ignition internal combustion engine of a vehicle, as a function of the engine load, and in each graph there is a cloud of error values associated with the operating parameter in a reference condition (indicated with R) and a cloud of error values associated with the same operating parameter in a condition of simulated variation (deviation) of the parameter (indicated with D), when it has decreased by a predetermined simulation amount representative of the consequence of a deviation in the behaviour of the injector apparatus with respect to the predetermined initial reference conditions (corresponding to the manufacturing setting conditions).

[0019] The error tolerance thresholds of 5% are also shown in all graphs.

[0020] In some cases, respectively for the parameters of air temperature at the intake manifold, temperature of the engine cooling water and temperature of the exhaust gases brought into recirculation, the error values are substantially coincident between the reference condition and the simulated deviation condition. On the contrary, for the pressure parameters at the intake manifold, relative position of the phase shifter and position of the exhaust gases recirculation valve the error values change between the reference condition and the simulated deviation condition.

[0021] As can be deduced from the graphs, the deviations that mostly influence the estimation of the amount of air in the combustion mixture by the electronics associated with the lambda probe are those that occur in the pressure at the intake manifold, and the values of the errors in the estimation of the amount of air in the combustion mixture are constantly lower than the 5% threshold only in a region of high engine load, for an amount of intake air equal to 85%.

[0022] This deduction is confirmed by the graph in figure 3, indicative of the percentage error in the estimation of the amount of air in the combustion mixture due to deviations in the pressure at the intake manifold as a function of the actual amount of air drawn in, in an experimental test conducted on the bench. The point cloud indicated with A shows the test result in a condition where the pressure at the intake manifold was forcibly increased by a predetermined test amount, the point cloud indicated with B shows the test result in a condition where the pressure at the intake manifold was forcibly decreased by a predetermined test amount. The point cloud indicated with R shows the error values associated with the pressure at the intake manifold in a reference condition, in the experimental test.

[0023] As can be noted, only for high or medium-high values of the engine load, i.e. the percentage of air drawn in, the error values are within the 5% threshold.

[0024] The aforementioned simulations and tests are based on predetermined models of the amount of injected fuel and the amount of combustion mixture air that reach the lambda probe, which can be simplified into linear models characterized only by a respective gain coefficient and a respective offset. In particular, if the pressure at the intake manifold is taken as a reference, the amount of fuel injected can be modelled by the formula: amount of fuel injected = (injection time - injection offset) * injector gain where the injection time is the time during which the electronics controls the injector actuation solenoid, the injection offset is the time elapsed from the start of the solenoid control to the time when the fuel begins to flow, and the injector gain is the ratio between the injected amount and the injection time excluding the injection offset transient phase.

[0025] The amount of air can be modelled by the formula: air amount = (intake duct pressure - partial pressure of the residual inert gas)

[0026] * gain

[0027] The models are advantageously stored on a stand-alone computer (e.g., a computer of a design office) to conduct the simulations separately from an engine control unit.

[0028] At medium or high engine loads the injection offset and the partial pressure of the residual inert gas are negligible so that a deviation in injector gain can be determined from measuring the oxygen concentration in the exhaust gases at the lambda probe.

[0029] This condition is verified, in a subsequent process validation step, through conformity tests conducted on a real vehicle representative of a predetermined propulsion system, including a predetermined engine model, a predetermined lambda probe and a predetermined engine control logic.

[0030] Based on the assumption demonstrated in the preceding discussion, that the data acquired by the lambda probe provide an accurate estimate of the deviation of the injected amount of fuel with respect to an optimal reference condition under high or medium-high load conditions where an error in the estimation of the amount of air in the combustion mixture is less than a predetermined threshold and therefore considered negligible, figure 4 shows a block diagram of a system 1 for estimating the amount of fuel injected in a spark ignition internal combustion engine of the invention.

[0031] Reference numeral 10 denotes a processing module for the estimation of a long-term adjustment factor (LTFT - Long Term Fuel Trim) of the amount of fuel delivered by at least one injector apparatus of a spark ignition internal combustion engine of a vehicle, according to the known art. This module is arranged to determine an adjustment of the amount of fuel delivered by at least one injector apparatus with respect to a reference condition from a plurality of signals or input data that include a first signal or data SI indicative of the concentration of oxygen in the exhaust gases detected by the lambda probe, a second signal or data S2 indicative of the engine rotational speed and a third signal or data S3 indicative of the engine load or of the torque delivered by the engine.

[0032] The output of the processing module 10, i.e. the values assumed over time by the estimated adjustment factor T of the fuel amount, is provided in input to a module 12 for estimating the amount (mass) of fuel injected over time through a selection module 14 arranged to forward a weighted estimate G of the adjustment factor of the amount of fuel received from the processing module 10 to the module 12 as a function of the value of a consensus binary data E present at a second consensus input. This weighted estimate of the adjustment factor of the amount of fuel is hereinafter referred to as the deviation factor G of the amount of fuel. The consensus binary data E is indicative of enabling or disabling the learning of the adjustment factor of the amount of fuel by the module 12 for estimating the amount of fuel (mass) injected over time as a function of the operating conditions of the engine in which the adjustment factor T of the amount of fuel was estimated. Specifically, the consensus binary data E is generated by a verification module 16 of the current operating conditions of the engine. The module 16 receives in input the signal or data S2 indicative of the engine rotational speed and the signal or data S3 indicative of the engine load that is of the torque delivered by the engine and stores a (or is arranged to consult an associated) pre-calibrated selection map (for example, a two-dimensional search table) that associates with each pair of values of engine rotational speed and engine load a value "0" or "1" of the consensus binary data, where "0" means unreliable value of the long-term adjustment factor (T) of the amount of fuel delivered, for the purpose of estimating the amount of fuel injected, and "1" means reliable value of the long-term adjustment factor (T) of the amount of fuel delivered for the purpose of estimating the injected amount of fuel, as a result of the determination that the adjustment factor T of the amount of fuel delivered is correctly estimated from the concentration of oxygen in the exhaust gases when the values of the errors in estimating the amount of air in the combustion mixture are less than a predetermined threshold, for example a threshold of 5% as determined by the foregoing considerations. More generally, the threshold is selected as a function of a compromise between calculation speed and accuracy on the estimate.

[0033] The pre-calibrated selection map is calibrated based on the results of the simulations and bench tests conducted as described with reference to figures 1-3, further validated by vehicle tests and with different sets of injectors.

[0034] The module 12 for estimating the amount (mass) of fuel injected over time is arranged to calculate an estimation of the amount (mass) F of fuel injected over time as a function of a second signal or input data S4 indicative of the injection time or - alternatively - indicative of the reference injection flow rate.

[0035] In the operation of a propulsion system of a vehicle, including a spark ignition internal combustion engine, a lambda probe adapted to detect the presence of oxygen in the exhaust gases and an engine control unit arranged to maintain the air / fuel mixture ratio within the optimal efficiency range of the catalytic converter mounted on the exhaust system of the vehicle, the system 1 for estimating the amount of fuel injected into a spark ignition internal combustion engine, conveniently integrated into the engine control unit or possibly made in a dedicated processing unit, is calibrated and operates as follows.

[0036] In a first initialization step, at the first engine start, at the engine start after reprogramming or at the resetting of the adaptive parameters of the lambda probe, which occurs following the replacement in the workshop of components of the injection system, the deviation factor G of the amount of fuel is set to a predetermined factory value and stored in a non-volatile memory associated with the engine control unit or the dedicated processing unit.

[0037] At each vehicle start, the system 1 is awakened and the deviation factor G of the amount of fuel is loaded from the memory into the module 12 for estimating the amount (mass) of fuel injected over time.

[0038] For the entire time in which the engine is running, a weighted estimate of the adjustment factor T of the amount of fuel is calculated, where the weight of the unreliable adjustment values of the amount of fuel is "0" and the weight of the reliable adjustment values of the amount of injected fuel is "1" as represented by the consensus binary data E generated by the verification module 16 of the current operating conditions of the engine, according to the pre-calibrated selection map that associates each pair of engine rotational speed and engine load values with a value "0" or " 1" of the consensus binary data E. The weighted estimate of the adjustment factor T of the amount of fuel is assumed as the value of the deviation factor G of the amount of fuel. This value is finally saved in the non-volatile memory associated with the engine control unit or with the dedicated processing unit when the engine operation is stopped. In an alternative embodiment, for the entire time that the engine is running, the value of the deviation factor G of the amount of fuel is updated to a filtered value of the adjustment factor T of the amount of fuel, when the consensus binary data E generated by the verification module 16 of the current operating conditions of the engine assumes value "1" (i.e. the adjustment values of the amount of injected fuel are considered reliable), or the value of the deviation factor G of the amount of fuel is maintained at the previous value when the consensus binary data E generated by the verification module 16 of the current operating conditions of the engine assumes value "0" (i.e. the adjustment values of the amount of injected fuel are considered unreliable). In the case of reliable adjustment values of the amount of injected fuel, the value of the adjustment factor T of the amount of fuel is filtered with a low-pass filter to eliminate spurious variations that may be due to over-elongations or under-elongations of the mixture titre caused by transient manoeuvres.

[0039] Of course, without prejudice to the principle of the invention, the embodiments and details of construction can vary widely with respect to what has been described and illustrated purely by way of non-limiting example, without departing from the scope of protection of the invention defined by the appended claims.

Claims

CLAIMS1. A method, implemented by means of electronic processing means, for estimating the amount of fuel injected into a spark ignition internal combustion engine with which a lambda sensor is associated, characterised by comprising the steps of: estimating over time values of a long-term adjustment factor (T) of the amount of fuel delivered by at least one injector apparatus of said spark ignition internal combustion engine from an amount of air in the combustion mixture estimated by said lambda sensor; determining, for each of said values of the estimated long-term adjustment factor (T) of the amount of fuel delivered, whether it is reliable or unreliable as a function of the operating conditions of the engine at which the estimation of the adjustment factor (T) of the amount of fuel delivered took place; and estimating the amount (mass) of fuel injected over time from the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered.

2. The method according to claim 1, wherein the values of the long-term adjustment factor (T) of the amount of fuel delivered are further estimated based on an engine rotational speed and a torque supplied by the engine.

3. The method according to any one of the preceding claims, wherein the engine operating conditions according to which a value of the long-term adjustment factor (T) of the amount of fuel delivered is marked as reliable or unreliable include an engine rotational speed and a torque supplied by the engine.

4. The method according to any one of the preceding claims, wherein a value of the long-term adjustment factor (T) of the amount of fuel delivered is marked as reliable for engine operating conditions wherein an error in estimating the amount of air in the combustion mixture is less than a predetermined threshold.

5. The method according to any one of the preceding claims, wherein the amount (mass) of fuel injected over time is further estimated as a function of the injection time or the reference injection rate.

6. The method according to any one of the preceding claims, wherein the estimation of the amount (mass) of fuel injected over time from the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered includes, for the time in which the engine is running, a weighted estimate of the long-term adjustment factor (T) of the amount of fuel delivered, where the weight of the unreliable values of the long-term adjustment factor (T) of the amount of fuel delivered is ‘0’ and the weight of the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered is ‘1’.

7. The method according to any one of claims 1 to 5, wherein estimating the amount (mass) of fuel injected over time from the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered includes, for the time in which the engine is running, calculating filtered values of the long term adjustment factor (T) of the amount of fuel delivered for reliable values of said long term adjustment factor (T) of the amount of fuel delivered, and retaining the previous value of the long term adjustment factor (T) of the amount of fuel delivered for unreliable values of said long term adjustment factor (T) of the amount of fuel delivered.

8. The method according to claim 7, wherein said filtered values of the long-term adjustment factor (T) of the amount of fuel delivered are filtered with a low-pass filter to eliminate spurious variations.

9. The method according to any one of the preceding claims, comprising an initialization step in which the long-term adjustment factor (T) of the amount of fuel delivered is set to a predetermined factory value, said initialization step being implemented at the first engine start, at the engine start after reprogramming or at the resetting of the adaptive parameters of the lambda sensor.

10. A system for estimating the amount of fuel injected into a spark ignition internal combustion engine with which a lambda sensor is associated, comprising: a processing module (10), arranged for the estimation over time of values of a longterm adjustment factor (T) of the amount of fuel delivered by at least one injector apparatusof said spark ignition internal combustion engine from an amount of air in the combustion mixture estimated by said lambda sensor; a verification module (16) of the current operating conditions of the engine, arranged to determine, for each of said values of the estimated long-term adjustment factor (T) of the amount of fuel delivered, whether it is reliable or unreliable as a function of the operating conditions of the engine at which the estimation of the adjustment factor (T) of the amount of fuel delivered took place, and to output a respective consensus binary data element (E) indicative of an unreliable value of the long-term adjustment factor (T) of the amount of fuel delivered or a reliable value of the long-term adjustment factor (T) of the amount of fuel delivered; a module (14) for selecting said long-term adjustment factor (T) of the amount of fuel delivered, arranged to provide a weighted estimate (G) of said long-term adjustment factor (T) of the amount of fuel delivered as a function of said consensus binary data element (E); and a module (12) for estimating the amount (mass) of fuel injected over time, adapted to receive in input said weighted estimate (G) of the long-term adjustment factor (T) of the amount of fuel delivered and arranged for calculating the estimate of the amount (mass) (F) of fuel injected over time from the reliable values of the long-term adjustment factor (T) of the amount of fuel delivered.

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