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

Abstract

A method for determining the air flow rate in a cylinder of a low-load internal combustion engine, said engine having at least one cylinder, at least one intake valve and one exhaust valve, and one intake chamber per cylinder, each intake chamber having a pressure sensor. Said method comprising the following steps: - first measurement of a pressure (MAP) in the intake chamber after the intake valve is closed; - second measurement of a pressure (MAP_UP) in the intake chamber before the intake valve is opened; - under predetermined conditions of engine speed and air intake 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 rate entering the cylinder from said representative parameter and the engine speed.Figure from the summary: Figure 4.

Description

Title of the invention: Method for determining air flow in an internal combustion engine

[0001] This disclosure relates to a method for determining an air flow rate in an internal combustion engine. technical field

[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 other engine applications (lawnmower or other mobile motorized tool, stationary engine, etc.).

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

[0004] In an internal combustion engine, a mixture of fuel and air burns in at least one combustion chamber. In each chamber, combustion performs work that is mechanically recovered by a piston sliding in a cylinder and connected by a connecting rod to a crankshaft. To optimize combustion, both from a fuel consumption standpoint and from the standpoint of limiting pollutant emissions, it is necessary to precisely determine the quantity of air admitted into the engine.

[0005] Measuring the airflow in an engine is based, in particular, on pressure measurements at the engine's air intake. A measurement is taken by measuring the vacuum created upstream of the cylinder by the intake stroke, when air is drawn into the cylinder. This vacuum is representative of the incoming airflow. However, other parameters, such as atmospheric pressure, are also taken into account when estimating the airflow entering a cylinder. To estimate atmospheric pressure, the pressure upstream of the cylinder is measured before the intake valve opens. This measured pressure will be close to the atmospheric pressure outside the engine if the air intake, generally controlled by a throttle valve, is wide open and if the engine speed is not too high.Atmospheric pressure is then determined from, firstly, the pressure measured before the intake valve opens upstream of the cylinder and, secondly, the throttle opening value and the engine speed. For . To determine the airflow entering the cylinder, it is known to use a mapping that provides the flow value from the engine speed and a pressure quotient corresponding to the ratio between the pressure (vacuum) measured at the end of intake (preferably before opening an exhaust valve) and the ambient pressure obtained as previously indicated.

[0006] When the measured pressure value is relatively close to the ambient pressure value (low vacuum), a small measurement error in the pressure will have a relatively significant impact on the quotient. Under certain conditions, a measurement error of only 10 mbar (approximately 1000 Pa) can lead to an error in the airflow rate that can exceed 10%.

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

[0008] Finally, at low load, slow combustion can lead to instabilities that are reflected at the intake, particularly during valve overlap (when the intake and exhaust valves are open simultaneously), by modifying the intake pressure value by a few millibars (1 mbar is approximately 100 Pa). Summary

[0009] The present disclosure improves the situation. Its purpose is, in particular, to provide a solution for determining more accurately the airflow entering an engine, especially under low load conditions. Preferably, this method will allow for greater accuracy without having to modify the pressure measurements taken. Furthermore, advantageously, this method will not require the use of new components in an engine to be implemented.

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

[0011] According to this 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; - under predetermined conditions of engine speed and air intake 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 rate entering the cylinder from said representative parameter and the engine speed.

[0012] Whereas in the prior art the airflow rate is determined from the value of the vacuum created in the intake chamber, corrected by the value of atmospheric pressure, it is proposed here to take into account the pressure variation during the filling of the intake chamber, that is to say, a factor proportional to the air entering 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] Calculations and tests have shown that the use of this new parameter makes it possible to obtain greater accuracy in determining the air flow rate and, above all, to be less sensitive to variations in the air pressure measured in the intake chamber.

[0014] To enable the determination of 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 one exhaust valve and, on the other hand, an intake chamber per cylinder, each intake chamber being disposed between an air inlet with variable opening and at least one intake valve of said cylinder and further comprising a pressure sensor.

[0015] According to this disclosure, this process includes 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 atmospheric pressure AMP - under predetermined conditions of engine speed and air intake 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 an air flow entering the cylinder from said representative parameter and the engine speed; - outside the predetermined conditions above, determination of an air flow entering the cylinder from said corrected parameter and engine speed.

[0016] In this process, the corrected parameter corresponds for example to the ratio between the first pressure measurement (MAP) and atmospheric pressure, that is: 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 representing 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 rate from the corrected parameter and a second determination of air flow rate from the parameter representing the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure, and an alert is created when the flow rate values ​​obtained, on the one hand, by the first determination of air flow rate, and, on the other hand, by the second determination of air flow rate, diverge beyond a predetermined tolerance range.

[0018] This advantageous variant makes it possible to detect abnormal engine operation corresponding for example to a camshaft misalignment 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 intake, 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 crossover point, that is to say 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 top dead center of combustion.

[0021] According to a preferred embodiment, the parameter representing the pressure variation between the first pressure measurement and the second pressure measurement as a function of 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 atmospheric pressure AMP and the first measured pressure, that is to say: PQ_LL = (MAP_UP - MAP) / (AMP - MAP).

[0022] For the processes proposed above, it is advantageously assumed that: - atmospheric pressure AMP is determined periodically as a function of a second pressure measurement in an engine intake chamber and engine speed; and / or - The value of the air flow rate 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 described above when this program is executed by a processor, in particular an electronic control unit of an internal combustion engine.

[0024] According to another aspect, a non-transient, computer-readable recording medium is proposed on which such a program is recorded. Brief description of the drawings

[0025] Other features, details and advantages will become apparent from reading the detailed description below and from analyzing the accompanying 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 curve of variation of flow measured for a given regime in using a first parameter. Fig. 3

[0028] [Fig.3] shows a curve of variation of flow measured for a given regime in using a second parameter. Fig. 4

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

[0030] This description relates to a four-stroke internal combustion engine with one intake chamber per cylinder. As is known to those skilled in the art, an internal combustion engine has one or more cylinders, each containing a combustion chamber. Each combustion chamber is associated with at least one intake valve to control the flow of gases entering the combustion chamber and at least one exhaust valve to control the flow of gases exiting the combustion chamber. At least one air intake with adjustable flow (generally by a device called a butterfly valve or "throttle") supplies the engine with fresh air. Knowing the airflow entering the engine is important for determining as precisely as possible the amount of fuel to inject in order to optimize combustion. limit both fuel consumption and pollutant emissions.

[0031] The following description applies to a four-stroke engine in which each cylinder has an associated intake chamber, that is, a separate space between an air inlet (for example, a throttle body) and the cylinder's intake valve(s). Each intake chamber is equipped with a pressure sensor. The case of a single-cylinder engine or a single cylinder of a multi-cylinder engine will be considered hereafter.

[0032] In a four-stroke engine, a complete work cycle is completed in two engine revolutions, or 720°CRK, as illustrated in [Fig. 1], which shows a pressure variation in the intake chamber during one engine cycle. [Fig. 1] represents a set of curves, each illustrating the pressure variation (on the y-axis) with respect to the angular position of the engine (on the x-axis). Each curve corresponds, for example, to a different air intake (throttle) opening, with the engine speed N being the same for each curve.

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

[0034] In the remainder of this description, for the sake of simplicity, we will refer only to a single intake valve and a single exhaust valve, and we will consider that the airflow into the engine is regulated by a butterfly valve mounted in a throttle body. This does not exclude embodiments with multiple intake valves and / or multiple exhaust valves and / or with another airflow regulation system, which are also included in this description.

[0035] It is proposed here, as already known, to take an initial pressure measurement (MAP value) when the piston reaches bottom dead center, after air has been admitted into the cylinder, that is, 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 taken when the intake valve is closed. This measurement is taken to measure the pressure in the intake chamber when it is close to its (absolute) minimum value, preferably when the value is at its minimum or when this value begins to increase again.

[0036] A second pressure measurement (MAP_UP value) is taken just before the crossover phase, when the intake valve is still closed. This second measurement is usually taken because this pressure is quite close to atmospheric pressure, and it is known that, based on the pressure measurement, and depending on the load and engine speed conditions, pressure learning can be performed. atmospheric and to obtain a good estimate of atmospheric pressure. Atmospheric pressure is subsequently referred to as AMP. As atmospheric pressure varies little (it changes with altitude), the AMP estimate is usually made periodically, when predetermined conditions are met (for example, an estimate is avoided at low load or high engine speed).

[0037] Typically, the incoming airflow is calculated from the MAP value, since this corresponds to the pressure drop created in the intake chamber by the air entering the combustion chamber and is therefore representative of the quantity of air entering the combustion chamber. This value is then corrected for atmospheric pressure, which influences how the intake chamber fills with air through the throttle body. The following ratio is then calculated:

[0038] PQ_AMP = MAP / AMP

[0039] It is then known how 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, a value which is multiplied by the atmospheric pressure AMP to obtain a first air flow rate: debl. The latter is thus given by a function g:

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

[0041] The debl value 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 method of determining the air flow entering the cylinder leads, in certain engine configurations and under certain conditions, to dispersions as illustrated in [Fig. 2]. This figure shows a curve in a coordinate system with PQ_AMP values ​​on the x-axis and a flow rate obtained from this quotient on the y-axis.

[0043] It can be seen in [Fig. 2] that a small variation in PQ_AMP, i.e., the measured MAP pressure value, for example 1%, leads, for certain values ​​of PQ_AMP, to much larger variations, up to 10 or 12% in the example given, in the calculated airflow rate. This leads to instability in the airflow rate values ​​obtained under certain conditions.

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

[0045] There are different ways to define the low load of the motor. In a known manner, for the electronic control of a motor, a setpoint torque is determined from which instructions are established to obtain the delivery of the Expected 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 the motor can deliver. The motor can be considered to be 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.

[0046] The load limit can also be defined for a given engine speed N by the TPS opening value of the throttle regulating the air intake. It is thus possible to determine a two-input table N and TPS that indicates which load (setpoint torque) corresponds to a TPS opening of the throttle at engine speed N, or to define a function f giving a limiting throttle opening as a function of engine speed N such that when the TPS opening of the throttle is less than or equal to this limiting throttle opening f(N), then the engine can be considered to be operating at low load.

[0047] Under low load conditions, it is proposed to determine a pressure quotient that no longer depends primarily on the vacuum measured in the vacuum chamber as a function of atmospheric pressure, but rather considers the pressure variation during the filling of the intake chamber, while also taking atmospheric pressure into account. This pressure variation is proportional to the quantity of air that fills the intake chamber and is subsequently transferred to the combustion chamber.

[0048] Thus, it is 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)

[0052] 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.

[0053] Figure 3 corresponds to Figure 2 but uses the coefficient PQ_LL. This coefficient is a combination of four pressure values. If these four pressure values ​​have the same error (for example, 1%), the value of the coefficient PQ_LL remains virtually unchanged in most cases (compared to the value of this coefficient obtained with the exact values). It is observed here that the resulting curve is essentially a straight line with a relatively shallow slope, so that the flow rate deb2 or DEB varies almost linearly with PQ_LL; that is, a small variation in PQ_LL results in a variation in the determined flow rate in roughly the same proportions. It has been found that most often, when using the coefficient PQ_LL, if the error in the pressure measurement is on the order of 1% (or x%) the error on the determined flow rate is less than 1% (or x%) compared to the actual flow rate.

[0054] The [Fig.4] is a logic diagram that summarizes a preferred embodiment of a process as described above.

[0055] 180°BTDC: MAP

[0056] At approximately 180°CRK corresponding to the top dead center of combustion of the cylinder considered, 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 top dead center of combustion, the intake chamber has been able to refill with fresh air, and the pressure inside it tends to equalize with the external pressure (atmospheric pressure AMP) since the only opening in the intake chamber is its air inlet, where the throttle body is located. The measurement taken 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 merely illustrative.

[0060] As mentioned above, the atmospheric pressure AMP is determined when conditions are favorable. This pressure is not generally determined at each engine cycle because it is an external factor that varies only (very) slowly compared to the other values ​​used for engine regulation. Using this atmospheric pressure value, AMP, stored or possibly updated, for example following the measurement of the MAP_UP pressure, 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 the opening of the air intake is determined. If the current opening value of the throttle valve (TPS) is less than the limit value f(N), the engine is considered to be operating at low load. Therefore, TPS is compared to f(N):

[0063] TPS <= f (N) ?

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

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

[0066] This illustrative quotient of the derivative of the pressure prevailing in the intake chamber is then used with the engine speed value to determine:

[0067] h (N, PQ_LL)

[0068] where h is a function allowing the determination of an air flow rate from the regime engine N and the quotient PQ_LL

[0069] If, on the other hand, TPS is greater than the value f (N), the motor is considered to be operating at normal or high load, and a flow rate calculation is performed 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 logic diagram, 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 the engine is operating at low load or not. This flow rate value is preferably corrected by a factor K which depends on the air temperature TA and / or the engine temperature TM.

[0073] After correction, the desired value is obtained:

[0074] DEB

[0075] the air flow entering the cylinder in question.

[0076] In an alternative embodiment, it is proposed to measure the air flow rate both with the function g and also with the function h. We then obtain, for the same pressure measurements under the same conditions (engine regime, atmospheric pressure, ...), two flow rate values: DEB_g and DEB_h.

[0077] These two flow rate 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 rate values ​​can be compared in different ways.

[0079] For example, we can 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] The difference in absolute value between these two values ​​can also be compared with either the maximum or the minimum value of these two values: I DEB_g - DEB_h I / MIN (DEB_g; DEB_h) or I DEB_g - DEB_h I / 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] A person skilled in the art knows different ways of comparing two values ​​in a relative manner.

[0082] If these values ​​are too far apart and trigger an alert, then a fault can be diagnosed, such as a camshaft misalignment. This allows for the detection of variations from one engine to another. Industrial application

[0083] The present technical solution can be applied in particular in motor control to improve the accuracy of this control.

[0084] The proposed method, and the corresponding means for implementing this method, make it possible to better determine the airflow entering the engine at low load. It is then possible to optimize fuel consumption and limit the emission of pollutants.

[0085] The proposed solution has the advantage, for measurements made at low load, of being insensitive to a delayed measurement due to the pressure sensor since the coefficient used is a coefficient of two pressure values ​​each time.

[0086] Still for low loads, it is noted that the quotient used allows (compared to the use of the quotient for normal or high loads): - to be less sensitive to errors in determining atmospheric pressure, - to be less sensitive to variations in the engine, such as valve clearance or an inaccurate angular position of the engine, - to be less sensitive to combustion instabilities.

[0087] 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] This disclosure is not limited to the proposed embodiment examples and variants described above, which are only examples, but encompasses all variants that a person skilled in the art may consider within the framework of the protection sought.

Claims

Demands

1. A method for determining the air flow rate 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, an intake chamber per cylinder, each intake chamber being disposed between a variable opening air inlet and at least one intake valve of said cylinder and further comprising a pressure sensor, the method being characterized in that it 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 the ratio between the first pressure measurement (MAP) and atmospheric pressure (AMP), i.e.: 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 the air flow entering the cylinder from the parameter representing the pressure variation between the first pressure measurement and the second pressure measurement as a function of 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 determination of air flow, and, on the other hand, by the second determination of air flow, diverge beyond a predetermined tolerance range.

2. The method according to claim 1, wherein: - during engine operation 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), - during normal or high load engine operation, 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).

3. A method according to any 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 intake, i.e. in a range between -180°CRK and -90°CRK before top dead center of combustion.

4. A method according to any one of claims 1 to 3, characterized in that the second pressure measurement (MAP_UP) is carried out before the crossover point, 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 top dead center of combustion.

5. A method according to any one of claims 1 to 4, characterized in that the parameter representing the pressure variation between the first pressure measurement and the second pressure measurement as a function of 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 atmospheric pressure AMP and the first measured pressure, that is to say: PQ_LL = (MAP_UP - MAP) / (AMP - MAP).

6. A method according to any 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.

7. A method according to any one of claims 1 to 6, characterized in that the value of the air flow rate entering the cylinder is corrected as a function of the air temperature and / or the engine temperature and / or the atmospheric pressure.

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

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