WO2024041960A1

WO2024041960A1 - Method for determining an air flow rate in an internal combustion engine

Info

Publication number: WO2024041960A1
Application number: PCT/EP2023/072649
Authority: WO
Inventors: Xavier Moine
Original assignee: Vitesco Technologies GmbH
Priority date: 2022-08-23
Filing date: 2023-08-17
Publication date: 2024-02-29
Also published as: FR3139161A1

Abstract

The invention relates to a method for determining the air flow rate in a cylinder of an internal combustion engine at low load, the engine comprising at least one cylinder, at least one intake valve and one exhaust valve and one intake chamber per cylinder, each intake chamber comprising a pressure sensor. The method comprises the following steps: • - first measurement of a pressure (MAP) in the intake chamber after closure of the intake valve; • - second measurement of a pressure (MAP_UP) in the intake chamber before opening of the intake valve; • - under predetermined engine speed and air inlet opening conditions, determining a parameter representative of the variation in pressure between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure; • - determining a flow rate of air entering the cylinder on the basis of the representative parameter and of the engine speed.

Description

Method for determining an air flow rate in an internal combustion engine

Description

[0001] The present disclosure concerns a method for determining an air flow rate in an internal combustion engine.

Technical area

[0002] The technical field of the present invention is thus the field of engine control for an internal combustion engine. This disclosure is intended in particular for a motor vehicle or similar (motorcycle, truck, etc.) but can also be used for another application of an engine (mower or other mobile motorized tool, stationary engine, etc.).

[0003] The present disclosure relates more particularly to internal combustion engines operating on a four-stroke cycle and which include a separate intake for each cylinder with a separate pressure sensor upstream of each cylinder. This could, for example, be a single-cylinder engine.

Prior art

[0004] In an internal combustion engine, a mixture of fuel and air burns in at least one combustion chamber. In each chamber, combustion provides work which is recovered mechanically by a piston sliding in a cylinder and connected by a connecting rod to a crankshaft. To optimize combustion, on the one hand from a consumption point of view and on the other hand from a point of view of limiting polluting emissions, it is necessary to precisely determine the quantity of air admitted into the engine.

[0005] A measurement of an air flow in an engine is in particular based on pressure measurements at the level of the air intake into the engine. A measurement is made by measuring the depression created upstream of the cylinder by the intake phase, when air is drawn into the cylinder. This depression is representative of the incoming air flow. However, other parameters, such as atmospheric pressure, are also taken into account to estimate the air flow entering a cylinder. To estimate atmospheric pressure, we measure the pressure upstream of the cylinder before the intake valve opens. This measured pressure will be close to the atmospheric pressure prevailing outside the engine if the air inlet, generally controlled by a butterfly, is wide open and if the engine speed is not too high. The atmospheric pressure is then determined from, on the one hand, the pressure measured before opening of the intake valve upstream of the cylinder and, on the other hand, the throttle opening value and engine speed. To then determine the air flow entering the cylinder, it is then known to use a map which provides the flow value from the engine speed and a pressure quotient corresponding to the ratio between the pressure (depression) measured at the end of admission (preferably before opening an exhaust valve) and the ambient pressure obtained as indicated previously.

[0006] When the value of the measured pressure is relatively close to the value of the ambient pressure (low depression), a small measurement error on the pressure will have a relatively significant impact on the quotient. Under certain conditions, a measurement error of only 10 mbar (i.e. approximately 1000 Pa) can lead to an error in the air flow which can go beyond 10%.

[0007] Furthermore, in the case of low loads, valve clearance will have a significant influence on the pressure measurement in the intake. This influence subsequently results in an erroneous estimate of the air flow entering the engine.

[0008] Finally, at low load, slow combustion can lead to instabilities which have repercussions on the intake, particularly when the valves cross over (when the intake and exhaust valves are open at the same time) by modifying the pressure value at the inlet of a few millibars (1 mbar is approximately 100 Pa).

Summary

[0009] This disclosure improves the situation. Its particular aim is to provide a solution for knowing more precisely the air flow entering an engine, particularly under low load conditions. Preferably, this process will allow greater precision to be obtained without having to modify the pressure measurements carried out. Furthermore, advantageously, this process will not require the use of new components in an engine to be able to be implemented.

[0010] A method is proposed for determining the air flow in a cylinder of an internal combustion engine during operation of the engine at low load, said engine comprising, on the one hand, at least one cylinder, each cylinder comprising at least one intake valve and one exhaust valve and, on the other hand, an intake chamber per cylinder, each intake chamber being arranged between an air inlet with variable opening and the at least one intake valve of said cylinder and further comprising a pressure sensor.

[0011] According to the present disclosure, this process comprises the following steps:

- first measurement of a pressure (MAP) in the intake chamber after closing the intake valve; - second measurement of a pressure (MAP_UP) in the intake chamber before opening of the intake valve;

- under predetermined conditions of engine speed and air inlet opening, determination of a parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure;

- determination of an air flow entering the cylinder from said representative parameter and the engine speed.

[0012] While in the prior art the air flow is determined from the value of the depression created in the intake chamber, corrected by the value of the atmospheric pressure, it is proposed to take into account here the pressure variation during filling of the intake chamber, that is to say a factor proportional to the air which enters this chamber and which will be transferred to the combustion chamber. The calculated parameter is also a function of atmospheric pressure because the air entering the intake chamber is at atmospheric pressure upstream of the inlet.

[0013] The calculations and tests showed that the use of this new parameter made it possible to obtain greater precision in determining the air flow rate and, above all, to be less sensitive to variations in the measured air pressure. in the intake chamber.

[0014] To make it possible to determine the air flow in the engine considered here, even when the engine is not operating at low load, the following method is proposed which is a method for determining the air flow in a cylinder of an internal combustion engine, said engine comprising, on the one hand, at least one cylinder, each cylinder comprising at least one intake valve and an exhaust valve and, on the other hand, a chamber admission per cylinder, each intake chamber being arranged between an air inlet with variable opening and the at least one intake valve of said cylinder and further comprising a pressure sensor.

[0015] In accordance with the present disclosure, this process comprises the following steps:

- first measurement of a pressure (MAP) in the intake chamber after closing the intake valve;

- second measurement of a pressure (MAP_UP) in the intake chamber before opening the intake valve;

- determination of a corrected parameter (PQ_AMP) corresponding to a corrected value of the first pressure measurement (MAP) as a function of the atmospheric pressure AMP

- under predetermined conditions of engine speed and air inlet opening, determination of a parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure and determination of a flow rate of air entering the cylinder from said representative parameter and the speed engine ;

- apart from the conditions predetermined above, determination of an air flow entering the cylinder from said corrected parameter and the engine speed.

[0016] In this process, the corrected parameter corresponds for example to the ratio between the first pressure measurement (MAP) and the atmospheric pressure, that is to say:

PQ_AMP = MAP / AMP.

[0017] According to an advantageous embodiment, the method comprises both the determination of the corrected parameter (PQ_AMP) and the determination of the parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure (PQ_LL), said method further comprises a first determination of air flow from the corrected parameter and a second determination of air flow from the parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure, and an alert is created when the flow values obtained, on the one hand, by the first determination of air flow, and, on the one hand, by the second determination of air flow, diverge beyond a predetermined tolerance range.

This advantageous variant makes it possible to detect abnormal operation of the engine corresponding for example to an offset of the camshaft of said engine.

[0019] To measure substantially the minimum pressure prevailing in the intake chamber, it is advantageously provided that the first pressure measurement (MAP) is carried out substantially at bottom dead center at the end of admission, that is to say in a range between -180°CRK and -90°CRK before the top dead center of combustion.

[0020] To also obtain the substantially maximum pressure prevailing in the intake chamber with the intake valve closed, it is advantageously proposed that the second pressure measurement (MAP_UP) is carried out before the crossing point, i.e. i.e. before the simultaneous opening of the intake and exhaust valves, in other words in a range between 270°CRK and 360°CRK after the top dead center of combustion, preferably between 300°CRK and 330°CRK after said combustion top dead center.

[0021] According to a preferred embodiment, the parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement in function of the atmospheric pressure is a quotient (PQ_LL) corresponding to a ratio between, on the one hand, the difference between the second measured pressure and the first measured pressure, and, on the other hand, the difference between the atmospheric pressure AMP and the first pressure measured, that is to say:

PQ_LL = (MAP_UP - MAP) / (AMP - MAP).

[0022] For the processes proposed above, it is advantageously expected that:

- the atmospheric pressure AMP is determined periodically as a function of a second pressure measurement in an intake chamber of the engine and the engine speed; and or

- the air flow value entering the cylinder is corrected according to the air temperature and/or the engine temperature and/or the atmospheric pressure.

[0023] According to another aspect, a computer program is proposed comprising instructions for implementing a method presented above when this program is executed by a processor, in particular an electronic control unit of a motor. internal combustion.

According to another aspect, a non-transitory recording medium, readable by a computer, on which such a program is recorded is proposed.

Brief description of the drawings

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the appended drawings, in which:

Fig. 1

[0026] [Fig. 1] shows pressure variations in an intake chamber of a cylinder as a function of the angular position of the corresponding engine.

Fig. 2

[0027] [Fig. 2] shows a flow variation curve measured for a given regime using a first parameter.

Fig. 3

[0028] [Fig. 3] shows a flow variation curve measured for a given regime using a second parameter.

Fig. 4

[0029] [Fig. 4] shows a flowchart for implementing a method according to the present disclosure. Description of embodiments

The present description is made in relation to an internal combustion engine, of the four-stroke type, for which there is one intake chamber per cylinder. In a manner known to those skilled in the art, an internal combustion engine comprises one or more cylinders, inside each of which there is a combustion chamber. Each combustion chamber is associated with at least one intake valve to manage gas flows entering the combustion chamber and at least one exhaust valve to manage gas flows leaving the combustion chamber. At least one air inlet with adjustable flow (generally by a device called a butterfly or “throttle” in English) makes it possible to supply the engine with fresh air. It is important to know the air flow entering the engine to most accurately determine the quantity of fuel to inject in order to optimize combustion to limit both fuel consumption and the emission of pollutants.

The following description is thus given for a four-stroke engine for which each cylinder is associated with an intake chamber, that is to say a separate space between an air inlet (for example a throttle body ) and the cylinder intake valve(s). Each intake chamber here is equipped with a pressure sensor. We will subsequently consider the case of a single-cylinder engine or only one cylinder of a multi-cylinder engine.

[0032] In a four-stroke engine, a complete work cycle is carried out over two engine revolutions, i.e. 720° CRK as illustrated in Figure 1 which illustrates a pressure variation in the intake chamber considered during a motor cycle. Figure 1 represents a set of curves which each illustrate the pressure variation (on the ordinate) relative to the angular position of the engine (on the abscissa). Each curve corresponds for example to a different air inlet opening (throttle), the engine speed N being the same for each curve.

[0033] In Figure 1, the position 0°CRK corresponds to the crossing top dead center, that is to say the passage through a top dead center of a piston sliding in the cylinder considered when the intake valves and exhaust are open. The 360°CRK position then corresponds to the top dead center of combustion.

[0034] In the remainder of the description, to simplify reading, we will only speak of a single intake valve, only a single exhaust valve and we will consider that the air flow at the engine inlet is regulated by a throttle mounted in a throttle body. This does not exclude embodiments with several inlet valves and/or several exhaust valves and/or with another air flow regulation system which are also included in the present description.

[0035] It is proposed here, as already known, to make a first pressure measurement (MAP value) when the piston arrives at its bottom dead center, after the admission of air into the cylinder, that is to say say at a position corresponding to 180°CRK, or close to this position, for example at +/- 30°CRK, preferably at +/- 20°CRK and even more preferably at +/- 10°CRK. This measurement is made when the inlet valve is closed. This measurement is made to measure the pressure in the intake chamber when it is close to its minimum (absolute) value, preferably when the value is minimum or when this value begins to increase again.

[0036] A second pressure measurement (MAP_UP value) is carried out just before the crossover phase, when the inlet valve is still closed. This second measurement is usually carried out because this pressure is quite close to the atmospheric pressure and it is known to carry out from the measurement of this pressure, depending on the load and operating conditions, to learn the atmospheric pressure and to obtain a good estimate of atmospheric pressure. Atmospheric pressure is hereinafter called AMP. As the atmospheric pressure varies little (it changes with altitude), the estimation of AMP is usually made periodically, when predetermined conditions are met (for example we avoid making an estimation at low load or at high speed) .

[0037] Usually, the incoming air flow rate is calculated from the MAP value, since this corresponds to the depression created in the intake chamber by the entry of air into the combustion chamber. and is therefore representative of the quantity of air entering the combustion chamber. This value is then corrected by atmospheric pressure which affects how well the intake chamber fills with air through the throttle body. We then calculate the following quotient:

[0038] PQ_AMP = MAP / AMP

[0039] It is then known to determine from a two-dimensional map, the input variables being the engine speed N on one side and the quotient PQ_AMP on the other side, to determine a value which is multiplied by the atmospheric pressure AMP to obtain a first air flow: deb1. The latter thus given by a function g:

[0040] deb1 = g (N, PQ_AMP) * AMP

The value deb1 is then preferably corrected by a coefficient K as a function of the air temperature (TA) and/or the engine temperature (TM) to obtain the desired flow rate: DEB. [0042] This way of determining the air flow entering the cylinder leads in certain engine configurations and in certain conditions to dispersions as illustrated in Figure 2. This figure shows a curve in a reference frame with values of PQ_AMP in abscissa and a flow rate obtained from this quotient on the ordinate.

[0043] We note in Figure 2 that a small variation in PQ_AMP, that is to say in the measured MAP pressure value, for example 1%, leads for certain values of PQ_AMP to much greater variations, going in the example given up to 10 or 12%, of the calculated air flow. This leads to instability in the air flow values obtained under certain conditions.

[0044] It is then proposed here, when the conditions leading to such instability are met, to determine the air flow rate differently. Therefore, when the engine is operating at low load, another method of determining the air flow entering the cylinder is described below.

[0045] There are different ways of defining the low engine load. In known manner, for the electronic control of a motor, a target torque is determined from which instructions are established to obtain the delivery of the planned torque. The motor can be considered to be operating at low load if the set torque is less than a given value, for example a percentage of the maximum torque that can be provided by the motor. We can consider that the motor is operating at low load if the set torque is less than, for example, 50% of the maximum torque. Another limit (for example set between 25% and 60%) can also be considered.

The load limit can also be defined for an engine speed N given by the opening value TPS of the throttle regulating the air inlet. It is thus possible to determine a table with double input N and TPS which indicates to which load (set torque) corresponds a TPS opening of the throttle at speed N or define a function f giving a limiting throttle opening as a function of speed N such that when the throttle opening TPS is less than or equal to this limiting throttle opening f(N), then we can consider that the engine is operating at low load.

[0047] Under low load conditions, it is proposed to determine a pressure quotient which no longer depends essentially on the depression measured in the depression chamber as a function of atmospheric pressure but which considers the pressure variation during filling of the vacuum chamber. the intake chamber while also taking into account the atmospheric pressure. This pressure variation is proportional to the quantity of air which fills the intake chamber and which will then be transferred into the combustion chamber. [0048] It is therefore proposed to take the following quotient:

[0049] PQ_LL = (MAP_UP - MAP) / (AMP - MAP)

[0050] A function h then gives, from this quotient PQ_LL and the engine speed, a flow rate value deb2:

[0051] deb2 = h (N, PQ_LL)

The value deb2 is then preferably corrected by a coefficient K as a function of the air temperature (TA) and/or the engine temperature (TM) to obtain the desired flow rate: DEB.

Figure 3 is a figure corresponding to Figure 2 but using the coefficient PQ_LL. This coefficient is a combination resulting from four pressure values. If these four pressure values are affected by the same error (for example 1%), the value of the coefficient PQ_LL is almost unchanged in most cases (compared to the value of this coefficient obtained with the exact values). We note here that the curve obtained is substantially a straight line of relatively low slope so that the flow rate deb2 or DEB varies substantially linearly with PQ_LL, that is to say that a small variation on PQ_LL leads to a variation on the determined flow rate substantially in the same proportions. It has been noted that most often, with use of the PQ_LL coefficient, if the error in the pressure measurement is of the order of 1% (or x%), the error in the determined flow rate is less than 1% (or x%) compared to the actual flow.

[0054] Figure 4 is a flowchart which summarizes a preferred embodiment of a method as described above.

[0055] 180°BTDC: MAP

[0056] At approximately 180° CRK corresponding to the top dead center of combustion of the cylinder in question, a pressure measurement in the intake chamber is carried out and gives a first measured pressure value MAP.

[0057] 300°ATDC: MAP_UP

[0058] At approximately 300° CRK, after the top dead center of combustion, the intake chamber was able to fill again with fresh air and the pressure inside it tends to balance with the external pressure (atmospheric pressure AMP) since the only opening of the intake chamber is its air inlet at which the butterfly is located. The measurement carried out gives a second measured pressure value MAP_UP.

[0059] As indicated above, the values of 180°CRK and 300°CRK are indicative data which depend on the engine and are not limiting but simply illustrative. As indicated above, the atmospheric pressure AMP is determined when the conditions for doing so are favorable. This pressure is generally not determined at each engine cycle because this pressure is an external data which only varies (very) slowly compared to the other values used for regulating an engine. Using this atmospheric pressure value, AMP, stored or possibly updated, for example following the measurement of the pressure MAP_UP, the pressure quotient PQ_AMP is determined:

[0061] PQ_AMP = MAP / AMP

[0062] From the known data N corresponding to the engine speed which is continuously measured, a limit value f (N) for opening the air inlet is determined. If the current throttle opening value TPS is lower than the limit value f (N), the motor is considered to be operating at low load. We therefore compare TPS to f (N):

[0063] TPS <= f (N)?

[0064] If TPS is less than or equal to the limit value (response 1), then the motor operates at low load and the quotient PQ_LL is calculated:

[0065] PQ_LL = (MAP_UP - MAP) / (AMP - MAP)

This illustrative quotient of the derivative of the pressure prevailing in the intake chamber is then used with the value of the engine speed to determine:

[0067] h (N, PQ_LL)

[0068] where h is a function making it possible to determine an air flow from the engine speed N and the quotient PQ_LL

[0069] If, on the other hand, TPS is greater than the value f (N), we consider that the motor is operating at normal or high load, and a flow rate calculation is carried out from a ratio given by a function g:

[0070] g (N, PQ_AMP)

[0071] By multiplying this ratio by the atmospheric pressure AMP which has already been introduced into the flowchart, an air flow rate is obtained.

[0072] Two parallel channels thus make it possible to obtain a value corresponding to an air flow rate, depending on whether or not the motor is operating at low load. This flow value is preferably corrected by a factor K which depends on the air temperature TA and/or the engine temperature TM.

[0073] After correction, we then obtain the desired value: [0074] DEB

[0075] the air flow entering the cylinder considered.

[0076] It is proposed in a variant embodiment to measure the air flow both with the function g and also with the function h. We then obtain for the same pressure measurements under the same conditions (speed, atmospheric pressure, etc.) two flow values: DEB_g and DEB_h.

[0077] These two flow values are naturally different but should normally be close to each other since they correspond to the same air flow entering the engine.

[0078] These flow values can be compared in different ways.

[0079] We can for example divide the largest of these values by the smallest: MAX (DEB_g; DEB_h) / MIN (DEB_g; DEB_h).

An alert can be created for example if this coefficient exceeds a value of 1.05 (i.e. 5%).

[0080] We can also compare the difference in absolute value between these two values with either the maximum value or the minimum value of these two values:

| DEB_g - DEB_h | / MIN (DEB_g; DEB_h) or

| DEB_g - DEB_h | / MAX (DEB_g; DEB_h)

An alert can be created for example if the first or second of these coefficients exceeds 0.05 (i.e. 5%).

[0081] Those skilled in the art know different ways of comparing two values relatively.

[0082] If these values are too far from each other and cause an alert, then a fault can be diagnosed, such as for example an offset of a camshaft. This makes it possible to detect dispersion from one engine to another.

Industrial application

[0083] This technical solution can be applied in particular in motor control to improve the precision of this control.

[0084] The proposed method, and the corresponding means for implementing this method, make it possible to better understand the air flow entering the engine at low load. It is then possible to optimize fuel consumption and limit the release of polluting materials. [0085] The proposed solution has the advantage, for measurements made at low load, of being insensitive to an offset measurement due to the pressure sensor since the coefficient used is a coefficient of two pressure values each time.

[0086] Still for low loads, we note that the quotient used allows (compared to the use of the quotient for normal or high loads):

- to be less sensitive to an error in determining the atmospheric pressure,

- to be less sensitive to variations in the engine, such as for example valve clearance or an inaccurate angular position of the engine,

- to be less sensitive to combustion instabilities. As indicated, however, this quotient can only be used for low engine loads and for engines comprising an intake chamber and a corresponding pressure sensor per cylinder.

[0088] The present disclosure is not limited to the proposed embodiments and the variants mentioned above, only by way of example, but it encompasses all the variants that those skilled in the art could consider in the context of of the protection sought.

Claims

[Claim 1] Method for determining the air flow in a cylinder of an internal combustion engine, said engine being characterized by a speed value (N) and comprising, on the one hand, at least one cylinder, each cylinder comprising at least one intake valve and one exhaust valve and, on the other hand, one intake chamber per cylinder, each intake chamber being arranged between an air inlet with variable opening and the at least an intake valve of said cylinder and further comprising a pressure sensor, the method being characterized in that it comprises the following steps:

- determination of a corrected parameter (PQ_AMP) corresponding to the ratio between the first pressure measurement (MAP) and the atmospheric pressure (AMP), that is to say: PQ_AMP = MAP / AMP,

- determination of a parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure (PQ_LL),

- a first determination of the air flow entering the cylinder from the corrected parameter (PQ_AMP) and the engine speed (N),

- a second determination of air flow entering the cylinder from the parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure (PQ_LL) and the engine speed (N ),

- creation of an alert when the flow values obtained, on the one hand, by the first air flow determination, and, on the one hand, by the second air flow determination, diverge beyond 'a predetermined tolerance range.

[Claim 2] Method according to claim 1, in which:

- during operation of the engine at low load, the value of the air flow entering the cylinder corresponds to the air flow value determined from said representative parameter (PQ_LL) and the engine speed (N),

- when operating the engine at normal or high load, the value of the air flow entering the cylinder corresponds to the air flow value determined from the corrected parameter (PQ_AMP) and the engine speed (N) .

[Claim 3] Method according to one of claims 1 to 2, characterized in that the first pressure measurement (MAP) is carried out substantially at bottom dead center at the end of admission, that is to say in a range between -180°CRK and -90°CRK before the top dead center of combustion.

[Claim 4] Method according to one of claims 1 to 3, characterized in that the second pressure measurement (MAP_UP) is carried out before the crossing point, that is to say before the simultaneous opening of the valves intake and exhaust, in other words in a range between 270°CRK and 360°CRK after the top dead center of combustion, preferably between 300°CRK and 330°CRK after said top dead center of combustion.

[Claim 5] Method according to one of claims 1 to 4, characterized in that the parameter representative of the pressure variation between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure is a quotient (PQ_LL ) corresponding to a ratio between, on the one hand, the difference between the second measured pressure and the first measured pressure, and, on the other hand, the difference between the atmospheric pressure AMP and the first measured pressure, i.e. -say: PQ_LL = (MAP_UP - MAP) / (AMP - MAP).

[Claim 6] Method according to one of claims 1 to 5, characterized in that the atmospheric pressure AMP is determined periodically as a function of a second pressure measurement in an intake chamber of the engine and the engine speed.

[Claim 7] Method according to one of claims 1 to 6, characterized in that the value of air flow entering the cylinder is corrected as a function of the air temperature and/or the engine temperature and /or atmospheric pressure.

[Claim 8] Non-transitory recording medium readable by a computer on which is recorded a program for implementing a method according to one of claims 1 to 7 when this program is executed by a processor, in particular a unit electronic control of an internal combustion engine.