IT201600073400A1 - METHOD TO CHECK THE UNBALANCE IN THE AIR-FUEL REPORT OF THE CYLINDERS OF AN INTERNAL COMBUSTION ENGINE - Google Patents

Description

"METHOD FOR CHECKING THE UNBALANCE IN THE AIR-FUEL RATIO OF THE CYLINDERS OF AN INTERNAL COMBUSTION ENGINE"

TECHNIQUE SECTOR

The present invention relates to a method for controlling the unbalance in the air-fuel ratio of the cylinders of an internal combustion engine.

ANTERIOR ART

As is known, an internal combustion engine, preferably a two-cylinder engine for a motorcycle, comprises a plurality of injectors, each of which injects the fuel into a respective cylinder which is connected, through a respective intake valve, to a supply duct to the inside of which flows a combustive fluid which passes through an intake manifold and to an exhaust duct through a respective exhaust valve.

Each injector is connected to a fuel supply circuit which provides a feed pump which draws the fuel from a tank and feeds it under pressure to the injector through a feed channel. The exhaust duct feeds the exhaust gases produced by combustion to an exhaust system, which emits the gases produced by combustion into the atmosphere. The internal combustion engine then comprises a control unit, which supervises the operation of the internal combustion engine and is made to drive, in particular, the injectors.

To comply with some legal requirements and, in particular, to allow the emissions of a motorcycle to be kept within acceptable limits, it is desirable that the control unit is also able to detect the air-fuel ratio of the cylinders to recognize any imbalances. in the air-fuel ratio of the cylinders or to recognize those situations in which the air-fuel ratio in one or more cylinders is different from the air-fuel ratio of the remaining cylinders, for example due to a malfunction of the specific cylinder, or a leak of the intake manifold, or a problem with the injector associated with the specific cylinder, or even a malfunction in the law of motion of the respective cam of the camshaft.

Typically, the average air-fuel ratio between the cylinders is calibrated through tests carried out at the end of the line, but it is not possible to recognize any imbalances in the air-fuel ratio of the cylinders themselves during normal operation of the internal combustion engine.

DESCRIPTION OF THE INVENTION

The object of the present invention is to provide a method for controlling the unbalance in the air-fuel ratio of the cylinders of an internal combustion engine, which method is free of the drawbacks described above and is at the same time easy and economical to implement.

According to the present invention, a method is provided for controlling the unbalance in the air-fuel ratio of the cylinders of an internal combustion engine according to what is claimed by the attached claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described with reference to the attached drawings, which illustrate some non-limiting examples of implementation, in which:

Figure 1 is a schematic view of an internal combustion engine, in particular a two-cylinder engine for a motorcycle;

Figure 2 illustrates the progress of the stock as a function of the degrees of engine angle in the case in which the cylinders of the internal combustion engine of Figure 1 are balanced;

- Figures 3 and 4 illustrate the trend of the stock as a function of the degrees of engine angle in the case in which the cylinders of the internal combustion engine of Figure 1 are not balanced, i.e. in the case in which the air-fuel ratio in a cylinder is different from the air-fuel ratio of the other cylinder;

Figure 5 illustrates the trend of an unbalance index calculated by means of the method for detecting the unbalance in the air-fuel ratio of the cylinders of an internal combustion engine which is the object of the present invention;

Figures 6 and 7 illustrate the imbalance index of Figure 5 compared with a further indicator of the imbalance; And

Figure 8 is a block diagram illustrating the method for controlling the unbalance in the air-fuel ratio of the cylinders of an internal combustion engine object of the present invention.

PREFERRED EMBODIMENTS OF THE INVENTION

In Figure 1, the number 1 indicates as a whole an internal combustion engine, preferably for motorcycles, in particular a two-cylinder engine for a motorcycle.

The internal combustion engine 1 comprises a number of injectors 2 (of a known type and not described in detail), each of which injects the fuel into a respective cylinder 3 (only one of which is illustrated in Figure 1). The cylinder 3 houses a piston 4 mechanically connected by means of a connecting rod to a driving shaft 5 to transmit to the driving shaft 5 the force generated by combustion inside the cylinder 3. A phonic wheel is keyed to the driving shaft 5 (not shown ) provided with 24 teeth and coupled to a sensor, which is able to detect the time elapsed between the passage of two consecutive teeth.

Each cylinder 3 is connected by means of a respective intake valve 7 to an adduction duct 6 inside which flows a combustive fluid which passes through an intake manifold 6 * of the internal combustion engine 1 and to an exhaust duct 8 by means of a respective discharge valve 9. The flow of the combustion fluid entering the internal combustion engine 1 is preferably regulated by a control member 11 located downstream of a filter 10 and which varies the passage section of the adduction duct 6. The intake manifold 6 * is substantially defined along the supply duct 6 between the intake valve 7 and the control member 11.

Each injector 2 is connected to a fuel supply circuit which provides a feed pump 12 which draws the fuel from a tank 13 and feeds it under pressure to the injector 2 through a feed channel 14.

The exhaust duct 8 feeds the exhaust gases produced by combustion to an exhaust system, which emits the gases produced by combustion into the atmosphere and normally comprises at least one catalyst 15 (possibly provided with an anti-particulate filter). The internal combustion engine 1 then comprises a control unit 16, which supervises the operation of the internal combustion engine 1 and is designed to drive, in particular, the injectors 2.

Furthermore, the control unit 16 is connected to a sensor 17 (typically a switching probe or a linear oxygen probe of the UHEGO or UEGO type - of a known type and not described in detail) which measures the average air / fuel ratio of the gases. upstream of the catalytic converter 15.

The sensor 17 is housed along the exhaust duct 8 and is hit by the exhaust gases produced by both cylinders 3.

According to a preferred variant, a plurality of sensors 17 is provided, each associated with a number of cylinders 3. According to a possible embodiment, a sensor 17 is provided for each bank of cylinders 3 provided in the internal combustion engine 1.

According to a preferred variant, each sensor 17 is hit by the exhaust gases produced by a maximum number of cylinders 3 equal to four.

According to a preferred variant, the internal combustion engine 1 is of the irregular combustion type, ie the combustions are not equidistant from each other; for example, in the case of a two-cylinder engine, the exhaust phase of the combustion cycle of a cylinder II occurs 270 ° after the exhaust phase of the combustion cycle of a cylinder I and the exhaust phase of the combustion cycle of cylinder I occurs 450 ° after the exhaust phase of the combustion cycle of cylinder II.

The strategy used by the control unit 16 to detect the imbalance in the air-fuel ratio of the cylinders 3 using the information provided by the sensor 17 is described below.

Initially, the signal detected by the sensor 17 is processed in such a way as to select an angular observation window DW expressed in degrees of engine angle equal to a complete combustion cycle achieved through two turns of the engine shaft 5 scanning an angle equal to 720 °. The angular observation window DW is associated with the combustion of both the cylinder 3 indicated with I and of the cylinder 3 indicated with II. The angular observation window DW is recognized by the control unit 16 through the signal coming from the phonic wheel sensor keyed to the end of the motor shaft 5 of which it detects the rotation speed.

The control unit 16 is therefore arranged to recognize within the angular observation window W the maximum value ^ MAX-Ìmaximum value of the signal detected by the sensor 17, the minimum value λΜΙΝ_ι of the signal detected by the sensor 17 and their respective position at the inside of the angular viewing window DW.

An imbalance index ISi is then calculated through the difference between the maximum value ^ MAX-Ì of the signal detected by the sensor 17 and the minimum value AMIN-Ì of the signal detected by the sensor 17 expressed as follows:

ISi unbalance index for the i-th combustion cycle;

^ MAX-Ì maximum value of the signal detected by the sensor 17;

λ · ΜΐΝ-ί minimum value of the signal detected by the sensor 17;

the combustion cycle in question.

The imbalance index ISi is higher the greater the difference between the two maximum and minimum values ÀMAXe λΜΙΝ, i.e. the greater the unbalance in the air / fuel ratio between the two cylinders 3.

For this reason, according to what is illustrated in Figure 5, the imbalance index ISi is subsequently compared with a threshold value TV to verify whether the i-th combustion cycle is balanced or not, i.e. to recognize those situations in which the air-fuel ratio in one cylinder 3 is different from the air-fuel ratio of the other cylinder 3.

The threshold value TV is determined in a preliminary tuning phase and as a function of the maximum imbalance index ISi determined during the test combustion cycles in which the air-fuel ratio of the cylinders 3 is balanced. According to a preferred variant, the maximum unbalance index ISi determined during the test combustion cycles in which the air-fuel ratio of the cylinders 3 is balanced is further increased by a safety margin Δ.

In the event that the imbalance index ISi is lower than the threshold value TV, the control unit 16 is arranged to recognize that the air-fuel ratio of the cylinders 3 in the combustion cycle just analyzed is balanced.

If the imbalance index ISi is higher than the threshold value TV, the control unit 16 is arranged to recognize that the air-fuel ratio of the cylinders 3 in the analyzed combustion cycle is unbalanced.

The control unit 16 is designed to recognize the occurrence of various conditions: the condition in which there is no imbalance in the air-fuel ratio of the cylinders 3, the condition in which there is a "lean" imbalance in the air-fuel ratio of a given cylinder 3 and finally the condition in which there is a "rich" imbalance in the air-fuel ratio of the given cylinder 3.

It is therefore necessary to recognize if the cylinder 3 indicated with II is richer or thinner than the cylinder 3 indicated with I. The control unit 16 then proceeds to identify the positions inside the angular observation window DW assumed respectively by the value ^ MAX-Ìmax of the signal detected by sensor 17 and from the minimum AMIN-Ìmin value of the signal detected by sensor 17.

Since the exhaust phase of the combustion cycle of the cylinder 3 indicated with II occurs 270 ° after the exhaust phase of the combustion cycle of the cylinder 3 indicated with I while the exhaust phase of the combustion cycle of the cylinder 3 indicated with I occurs 450 ° after the exhaust phase of the combustion cycle of the cylinder 3 indicated with II, the flow rate of exhaust gases emitted by the cylinder 3 indicated with I has a residence time near the sensor 17 which is less than the residence time in the vicinity of the sensor 17 of the cylinder 3 indicated with II.

According to what is illustrated in Figure 3, in fact, in the case in which the cylinder 3 indicated with II is thinner than the cylinder 3 indicated with I, the transition phase from the maximum AMAXJ value to the minimum value λΜΙΝ_ι of the signal detected by the sensor 17 and expressed through the motor angle ΘΜΑΧ-ΜΙΝ is faster than the transition from the value λ · ΜΐΝ-ίminimo to the value λMAX-Ìmaximum value of the signal detected by the sensor 17 and expressed through the motor angle ΘΜΙΝ-

MAX

Vice versa, according to what is illustrated in Figure 4, if the cylinder 3 indicated with II is richer than the cylinder 3 indicated with I, the transition phase from the minimum AMIN-Ìmin value to the AMAX-Ìmaximum value expressed through the engine angle ΘΜΙΝ -ΜΑΧis faster than the transition from the XMAX_ ± maximum value to the minimum λΜΙΝ_ι value of the signal detected by the sensor 17 expressed through the motor angle ΘΜΑΧ-ΜΙΝ ·

Therefore, in the case in which the cylinder 3 indicated with II is thinner than the cylinder 3 indicated with I, the absolute value of the distance expressed in degrees of engine angle between the point in which the maximum AMAX-Ì value is obtained and the point in which the minimum AMIN-Ì value is obtained in the angular observation window DW of the signal detected by the sensor 17, it results:

- less than half of the entire combustion cycle (i.e. less than 360 ° of engine angle) if the maximum AMAX-Ì value precedes the minimum AMAX-Ì value; or alternatively

- greater than half of the entire combustion cycle (i.e. greater than 360 ° of engine angle) if the minimum AMIN-Ì value precedes the maximum AMAX-Ì value.

On the contrary, in the case in which the cylinder 3 indicated with II is richer than the cylinder 3 indicated with I, the absolute value of the distance expressed in degrees of engine angle between the point where the maximum AMAX-Ì value is obtained and the point in where we have the minimum value λΜΙΝ_ι in the angular observation window DW of the signal detected by the sensor 17 results:

- greater than half of the entire combustion cycle (i.e. greater than 360 ° of engine angle) if the maximum ÀMAXJ value precedes the minimum λΜΙΝ_ι value; or alternatively

- less than half of the entire combustion cycle (i.e. less than 360 ° of engine angle) if the minimum λΜΙΝ_ι value precedes the maximum ÀMAXJ value.

It is therefore also necessary to define a state of the unbalance, that is to define the sign of the unbalance towards the cylinder 3 indicated with II or towards the cylinder 3 indicated with I, in addition to the unbalance index ISi.

Figures 6 and 7 illustrate the result of some experimental tests conducted through an indicator which assumes a value of zero if the two cylinders 3 are balanced (i.e. if the imbalance index ISi is lower of the threshold value TV), assumes a value equal to - 1 in the case in which the cylinder 3 indicated with II is thinner than the cylinder 3 indicated with I and assumes a value equal to 1 in the case in which the cylinder 3 indicated with II is more of the cylinder 3 indicated with I. In addition to the indicator just described, the imbalance detected by two sensors predisposed to measure the air / fuel ratio of the exhaust gases exiting from a respective cylinder 3 is also illustrated. The indicator correctly recognizes both the cases in which the two cylinders 3 are balanced (figures 6 and 7), and the cases in which the cylinder 3 indicated with II is leaner than the cylinder 3 indicated with I (figure 6), and the cases in which the cyl or 3 indicated with II is richer than cylinder 3 indicated with I (figure 7).

Once it has been recognized whether in the combustion cycle analyzed the cylinder 3 indicated with II is richer or leaner than the cylinder 3 indicated with I, the control unit is predisposed to correct the quantity of fuel injected into the cylinder 3 indicated with II, according to what better described in the following discussion (with reference to figure 8).

According to a further variant, the above description finds advantageous application also in the case of an internal combustion engine 1 of the regular combustion type, ie in which the combustions are equidistant from each other. In the event that the imbalance index ISi is higher than the threshold value TV, the control unit 16 is set up to recognize that the air-fuel ratio of the cylinders 3 in the combustion cycle just analyzed is unbalanced, but to recognize whether the cylinder 3 indicated with II is richer or thinner than the cylinder 3 indicated with I it is not possible to proceed as described in the preceding discussion. In this case, the control unit is set up to step up the quantity of fuel injected into any one of the cylinders 3. In this way, knowing the combustion sequence of the cylinders 3 and knowing the cylinder 3 affected by the step increase of the quantity of fuel injected, it is possible to observe the angular observation window DW to verify, in subsequent combustion cycles, the effect produced by the step increase of the quantity of fuel injected into cylinder 3. In the case of a two-cylinder engine, when the The imbalance index ISi remains higher than the threshold value TV for a certain number of combustion cycles that follow, then the control unit 16 is arranged to correct the quantity of fuel injected into the other cylinder 3.

Furthermore, according to a preferred variant, in the case of a switching-type probe 17 during the transient phases in which it operates with a title in a neighborhood of 1, alternating lean combustion cycles with rich combustion cycles to optimize the operation of the catalyst 15 , it is possible to disable the strategy used by the control unit 16 to detect the imbalance in the air-fuel ratio of the cylinders 3 to avoid false recognitions.

According to a preferred variant, in order to avoid false recognitions, the control unit 16 is also configured to recognize the state of the unbalance, that is to recognize the sign of the unbalance towards the cylinder 3 indicated with II or towards the cylinder 3 indicated with I , in addition to the imbalance index ISi, only in the case in which the state of the imbalance is maintained for a given number N of combustion cycles. In other words, a combustion cycle must have proceeded from N-1 combustion cycles with the same state of the imbalance to be taken into account by the control unit 16. Since it has been verified that the unbalance of the cylinders 3 is mainly caused by dirtying and / or aging of components of the injection system, it is assumed that the unbalance of the cylinders 3 cannot change sign very quickly. Clearly, the greater the number N of combustion cycles considered, the more robust is the recognition of the unbalance of the cylinders 3, but at the same time, the slower the recognition of the unbalance of the cylinders 3, and vice versa.

According to a further variant, it is possible to use the signal detected by the sensor 17 processed in such a way as to select an angular observation window DW 'expressed in degrees of engine angle equal to a multiplicity of complete combustion cycles. An imbalance index ISi is then calculated for each complete combustion cycle inside the angular observation window DW '; the control unit 16 is then configured to calculate the average value IS of the imbalance indices calculated for the same observation angular window DW 'and compare it with a threshold value VT to recognize any imbalances in the air-fuel ratio of the cylinders 3. In alternatively, the control unit 16 proceeds by discarding the maximum ISMAX value and the minimum ISMIN value between the imbalance indices ISi calculated for the same angular observation window DW ', calculating the average value of the remaining unbalancing indices and comparing this average value with a threshold TV value to recognize any imbalances in the air-fuel ratio of the cylinders 3.

As illustrated in Figure 8, in block 100 the control unit 16 determines by means of maps stored inside the control unit 16 itself the theoretical flow rate of fuel to be injected into each cylinder 3 at each engine cycle under ideal conditions ( that is, in the case in which the air-fuel ratio of the cylinders 3 is balanced). The theoretical flow rate of fuel to be injected into each cylinder 3 is used to determine the actual flow rate of fuel to be injected into each cylinder 3 together with two other contributions. In particular, the sensor 17 located downstream of the cylinders 3 measures the average air / fuel ratio of the exhaust gases which is used inside a closed loop controller 110 which provides the first contribution to determine the actual average flow rate of fuel to be injected. in each cylinder 3.

The sensor 17 located downstream of the cylinders 3 also provides the unbalance index ISi and the unbalance status of the single cylinder 3 according to what is described in the preceding discussion which are used inside a closed loop controller 120 which provides the second contribution to determine the effective flow rate of fuel to be injected into each cylinder 3.

The unbalance index ISi and the unbalance status of the single cylinder 3 are then used to correct adaptive MAPSi maps of the cylinders 3 in the case in which quasi-stationary or slow transient operating conditions are verified, that is to say in the case in which the speed of rotation of the internal combustion engine 1 is included within a defined interval for a defined time interval; if the load index is included within a defined range of values, for a defined time interval; if the temperature of the internal combustion engine 1 falls within a defined range of values, for a defined time; in the case in which the first derivative in time of the speed of the internal combustion engine 1 is lower than a threshold value, for a defined time; and in the event that no malfunction has been diagnosed with the sensor 17, the fuel injection system or the air system. In particular, an adaptive MAPSi map is provided for each individual cylinder 3 comprising a number of cells defined as a function of the operating conditions, identified by the rotation speed of the internal combustion engine 1 expressed in rpm and by the load index of the combustion engine. internal.

In the event that the difference between the actual fuel flow rate and the theoretical fuel flow rate to be injected into each cylinder 3 at each engine cycle is greater than a limit LV value, the control unit 16 is set up to recognize a malfunction. a component between the sensor 17, the fuel injection system or the air system of the affected cylinder 3 and for generating a malfunction warning signal. The limit LV value is determined in a preliminary tuning phase taking into consideration the maximum aging and dirty effects to which the sensor 17, the fuel injection system or the air system of the cylinder 3 concerned may be subjected.

The method for detecting and controlling the imbalance in the air-fuel ratio of the cylinders 3 of an internal combustion engine 1 described up to now has several advantages. First of all, this method allows you to quickly and reliably determine if there is an imbalance in the air-fuel ratio of the cylinders 3 without the need to install additional components, without the need to make any type of model of the air system, but only through the information coming from the sensor 17 already provided in the internal combustion engine 1, only by calibrating a few simple parameters. Furthermore, this method also makes it possible to identify which cylinder 3 is characterized by a richer or leaner air-fuel ratio than the remaining cylinders 3.

Experimental tests have shown that the method described up to now guarantees good performances, in terms of reliability and precision of the determination of the unbalances in the air-fuel ratio, at all rotation speeds without excessively compromising the computational burden of the control unit 16.

1.- Method for checking the unbalance in the air-fuel ratio of the cylinders (3) of an internal combustion engine (1); wherein the internal combustion engine (1) comprises a plurality of cylinders (3) connected to an exhaust duct (8) which supplies the exhaust gases produced by combustion in the cylinders (3) to an exhaust system; and at least one sensor (17) housed along the exhaust duct (8) to be hit by the exhaust gases produced by the plurality of cylinders (3) and able to measure the air / fuel ratio of the exhaust gases; the method involves the steps of:

determining the theoretical flow rate (riii) of fuel to be injected into each cylinder (3) and at each cycle if the air-fuel ratio of the cylinders (3) is balanced;

detecting the signal coming from the sensor (17); determining the average air / fuel ratio of the exhaust gases through the signal coming from the sensor (17);

calculating an indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) through the signal coming from the sensor (17); And

determine the effective flow rate (mreai) of fuel to be injected into each cylinder (3) in

Claims (1)

CLAIMS 1.- Method for checking the unbalance in the air-fuel ratio of the cylinders (3) of an internal combustion engine (1); wherein the internal combustion engine (1) comprises a plurality of cylinders (3) connected to an exhaust duct (8) which supplies the exhaust gases produced by combustion in the cylinders (3) to an exhaust system; and at least one sensor (17) housed along the exhaust duct (8) to be hit by the exhaust gases produced by the plurality of cylinders (3) and able to measure the air / fuel ratio of the exhaust gases; the method involves the steps of: determining the theoretical flow rate (riii) of fuel to be injected into each cylinder (3) and at each cycle if the air-fuel ratio of the cylinders (3) is balanced; detecting the signal coming from the sensor (17); determining the average air / fuel ratio of the exhaust gases through the signal coming from the sensor (17); calculating an indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) through the signal coming from the sensor (17); And determine the effective flow rate (mreai) of fuel to be injected into each cylinder (3) as a function of the theoretical fuel flow rate (iti), the average air / fuel ratio of the exhaust gases and the indicator (ISi) of the unbalance in the air ratio - fuel of cylinders (3). 2. A method according to Claim 1, wherein the average air / fuel ratio of the exhaust gases detected by the sensor (17) is used inside a first closed loop controller (110). 3.- Method according to Claim 1 or 2, in which the step of calculating an indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) through the signal coming from the sensor (17) provides for: selecting a first angular observation window (DW) expressed in degrees of engine angle within the signal detected by the sensor (17), in which the first angular observation window (DW) is equal to at least one complete combustion cycle; recognize within the first angular observation window (DW) the maximum (AMAX-Ì) value and the minimum (AMIN-Ì) value of the signal detected by the sensor (17); calculating the indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) through the difference between the maximum value (AMAX-Ì) and the minimum value (λΜιΝ_ι) of the signal detected by the sensor (17); comparing the indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) with a threshold value (TV); And recognize the presence of an imbalance in the air-fuel ratio of the cylinders (3) if the indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) is higher than the threshold value (TV). 4.- Method according to one of the preceding claims, in which the indicator (ISi) of the unbalance in the air-fuel ratio of the cylinders (3) detected by the sensor (17) is used inside a second controller (120) in closed loop. 5.- Method according to one of the preceding claims and comprising the further step of correcting adaptive maps (MAPSi) of the cylinders (3) in the event that quasi-stationary or slow transient operating conditions are verified as a function of the indicator (ISi ) of the unbalance in the air-fuel ratio of the cylinders (3) detected by the sensor (17). 6. A method according to one of the preceding claims, and comprising the further step of calculating the difference between the actual fuel flow rate (mreai) and the theoretical fuel flow rate (riu) to be injected into each cylinder (3); And recognize a malfunction in the event that said difference is greater than a limit value (LV). 7.- Method according to Claim 6, in which the limit value (LV) is determined in a preliminary setting phase taking into account the maximum aging and dirty effects to which the sensor (17), the system fuel injection system and the cylinder air system (3).