Method for determining air flow in internal combustion engine

Abstract

A method is disclosed for determining the flow of air into cylinders of an internal combustion engine under 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:-measuring the pressure (MAP) in the intake chamber for a first time after the intake valve has been closed; -measuring the pressure (MAPUP) in the intake chamber for a second time before the intake valve is opened; -determining a parameter characterizing a pressure change between the first pressure measurement value and the second pressure measurement value as a function of atmospheric pressure under predetermined engine speed and air inlet opening conditions; -determining the air flow into the cylinder using the characterization parameter and the engine speed.

Description

Technical Field

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

[0002] The technical field of the invention is therefore that of engine control for internal combustion engines. The present disclosure is particularly intended for motor vehicles or the like (motorcycles, trucks, etc.), but may also be used for another application of an engine (lawn mower or other mobile power tool, static engine, etc.).

[0003] More particularly, the present disclosure relates to an internal combustion engine operating in a four-stroke cycle and comprising a separate intake port for each cylinder, wherein a separate pressure sensor is upstream of each cylinder. In this case, the engine may be, for example, a single-cylinder engine. Background Art

[0004] In an internal combustion engine, a mixture of fuel and air is burned in at least one combustion chamber. In each chamber, the combustion provides work that is mechanically recovered by a piston that slides in a cylinder and is connected to the crankshaft via a connecting rod. In order to optimize the combustion in terms of consumption on the one hand and pollutant emissions on the other hand, the amount of air admitted into the engine should be accurately determined.

[0005] The measurement of the air flow in the engine is based in particular on the pressure measurement at the air intake in the engine. When air is sucked into the cylinder, the measurement is obtained by measuring the vacuum generated upstream of the cylinder until the intake phase. This vacuum represents the incoming air flow. However, when estimating the air flow into the cylinder, other parameters (in particular the atmospheric pressure) are also taken into account. In order to estimate the atmospheric pressure, the pressure upstream of the cylinder is measured before the intake valve opens. If the air inlet (usually controlled by the throttle) is wide open and if the engine speed is not too high, the measured pressure will be close to the atmospheric pressure outside the engine. Then, the atmospheric pressure is determined using the pressure measured upstream of the cylinder before the intake valve opens on the one hand and the throttle opening value and the engine speed on the other hand. In order to determine the air flow into the cylinder, it is known to use a cartographie that uses the engine speed and a pressure quotient to provide a flow value, which corresponds to the ratio between the pressure (vacuum) measured after the intake (preferably before opening the exhaust valve) and the ambient pressure obtained as indicated above.

[0006] If the measured pressure value is relatively close to the ambient pressure value (low vacuum), a small measurement error of the pressure will have a relatively large impact on the quotient. Under certain conditions, a measurement error of only 10 mbar (about 1000 Pa) will lead to an error of more than 10% in the air flow.

[0007] Furthermore, at low loads, the valve clearance will have a significant effect on the pressure measurement in the intake port. This effect can lead to an erroneous estimate of the air flow into the engine.

[0008] Finally, at low loads, slow combustion may lead to instabilities affecting the intake charge, especially when valve overlap occurs (when the intake and exhaust valves open simultaneously), thus changing the intake pressure value by several millibars (1 mbar is roughly 100 Pa). Summary of the invention

[0009] The present disclosure aims to improve this situation. The present disclosure is particularly intended to provide a solution to more accurately determine the air flow into the engine, especially under low load conditions. Preferably, this method will provide greater accuracy without having to modify the pressure measurement implemented. In addition, advantageously, implementing this method will not require the use of new components in the engine.

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

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

[0012] - first measurement of the pressure in the intake chamber (MAP) after the intake valve has closed;

[0013] - A second measurement of the pressure in the intake chamber before the intake valve opens (MAP_UP);

[0014] - determining a parameter characterizing the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure under predetermined engine speed and air inlet opening conditions;

[0015] - Using said characteristic variable and the engine speed, determining the air flow into the cylinder.

[0016] While in the prior art the air flow is determined using the value of the vacuum created in the intake chamber (this value being corrected by the value of the atmospheric pressure), it is proposed here to take into account the pressure variation when the intake chamber is filled, i.e. a coefficient proportional to the air entering this chamber and to be transferred to the combustion chamber. The calculated parameter is also a function of the atmospheric pressure, since the air entering the intake chamber is at the atmospheric pressure upstream of the inlet.

[0017] Calculations and tests have shown that the use of this novel parameter ensures greater precision in determining the air flow and, in particular, less sensitivity to variations in the air pressure measured in the intake chamber.

[0018] In order 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 into the cylinders of an internal combustion engine, the 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, comprising an intake chamber per cylinder, each intake chamber being arranged between a variable-opening air inlet and the at least one intake valve of the cylinder and additionally comprising a pressure sensor.

[0019] According to the present disclosure, the method comprises the following steps:

[0020] - first measurement of the pressure in the intake chamber (MAP) after the intake valve has closed;

[0021] - A second measurement of the pressure in the intake chamber before the intake valve opens (MAP_UP);

[0022] - determining a correction parameter (PQ_AMP) corresponding to a correction value of the first pressure measurement (MAP) corrected as a function of the atmospheric pressure AMP;

[0023] - determining a parameter characterizing the pressure variation between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure under predetermined engine speed and air inlet opening conditions, and determining the air flow into the cylinder using said characterizing parameter and the engine speed;

[0024] - In addition to the above predetermined conditions, the air flow into the cylinder is determined using the correction parameter and the engine speed.

[0025] In this method, the correction parameter corresponds, for example, to the ratio between the first pressure measurement (MAP) and the atmospheric pressure, namely:

[0026] PQ_AMP=MAP / AMP.

[0027] According to an advantageous embodiment form, the method involves the following two steps: determining a correction parameter (PQ_AMP) and determining a parameter (PQ_LL) characterizing the pressure variation between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure,

[0028] The method further includes determining the air flow rate a first time using the correction parameter and determining the air flow rate a second time using a parameter characterizing a change in pressure between the first pressure measurement and the second pressure measurement as a function of atmospheric pressure; and

[0029] When the flow value obtained by the first determination of the air flow on the one hand and the flow value obtained by the second determination of the air flow on the other hand differ by more than a predetermined tolerance range, an alarm is generated.

[0030] This advantageous variant makes it possible to detect abnormal operation of the engine, such as a camshaft deviation of said engine.

[0031] In order to measure essentially the minimum pressure prevailing in the intake chamber, provision is advantageously made that a first pressure measurement value (MAP) is taken essentially at the intake end bottom dead center, ie in the range between -180° C. RK and -90° C. RK before combustion top dead center.

[0032] In order to also obtain the maximum pressure prevailing in the intake chamber when the intake valve is closed, it is advantageously proposed that a second pressure measurement value (MAP_UP) is acquired before the overlap point, i.e. before the intake valve and the exhaust valve open simultaneously, i.e. in the range between 270°C RK and 360°C RK after combustion top dead center, preferably in the range between 300°C RK and 330°C RK after said combustion top dead center.

[0033] According to a preferred embodiment form, the parameter characterizing 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 the 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.:

[0034] PQ_LL=(MAP_UP-MAP) / (AMP-MAP).

[0035] For the method proposed above, it is advantageous to propose:

[0036] - periodically determining the atmospheric pressure AMP as a function of a second pressure measurement in the intake chamber of the engine and the engine speed; and / or

[0037] - Correction of the value of the air flow into the cylinder as a function of the air temperature and / or the engine temperature and / or the atmospheric pressure.

[0038] According to another aspect, a computer program is proposed, comprising instructions for implementing the method as described above when the program is executed by a processor, in particular an electronic control unit of an internal combustion engine.

[0039] According to another aspect, a non-transitory computer-readable recording medium having such a program recorded thereon is provided. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] Other features, details and advantages will become apparent upon reading the following detailed description and from examining the accompanying drawings, in which:

[0041] Figure 1 The pressure variation in the cylinder intake chamber as a function of the angular position of the corresponding engine is shown.

[0042] Figure 2 A curve showing the change in flow rate measured for a given speed using a first parameter is shown.

[0043] Figure 3 A curve showing the change in flow rate measured for a given speed using a second parameter is shown.

[0044] Figure 4 A logic diagram for implementing a method according to the present disclosure is shown. DETAILED DESCRIPTION

[0045] The present description relates to a four-stroke internal combustion engine for which there is one intake chamber per cylinder. As known to those skilled in the art, an internal combustion engine comprises one or more cylinders, each of which comprises a combustion chamber. Each combustion chamber is associated with at least one intake valve for managing the airflow entering the combustion chamber and at least one exhaust valve for managing the airflow leaving the combustion chamber. At least one adjustable flow air inlet (usually controlled by a device called a throttle) is used to supply fresh air to the engine. It is important to know the air flow entering the engine in order to determine as accurately as possible the amount of fuel to be injected in order to optimize combustion, and thereby limit both fuel consumption and pollutant emissions.

[0046] Therefore, the following description relates to a four-stroke engine in which each cylinder is associated with an intake chamber (i.e. a separate space between the air inlet (e.g. throttle housing) and the intake valve(s) of the cylinder). In this case, each intake chamber is equipped with a pressure sensor. The following description relates to a single-cylinder engine or to a single cylinder of a multi-cylinder engine.

[0047] In a four-stroke engine, a complete working cycle is performed within two engine revolutions (i.e., 720°C RK), such as Figure 1 As illustrated in , the figure illustrates the pressure variation in the intake chamber in question during one engine cycle. Figure 1A set of curves is shown, each curve illustrating the pressure variation (on the Y axis) relative to the angular position of the engine (on the X axis). Each curve corresponds, for example, to a different (throttle) air inlet opening, the engine speed N being the same for each curve.

[0048] exist Figure 1 In the example, the position 0°C RK is the overlap top dead center, i.e. when the piston sliding in the cylinder in question passes the top dead center with the inlet and exhaust valves open. Thus, the position 360°C RK is the combustion top dead center.

[0049] In order to simplify the rest of the description, reference is made to only one intake valve and only one exhaust valve, and the air flow into the engine is considered to be regulated by a throttle mounted in a throttle housing. This does not exclude embodiments with several intake valves and / or several exhaust valves and / or with another system for regulating the air flow, which are also covered by the description.

[0050] As is already known, it is proposed here that a first pressure measurement value (value MAP) is taken when the piston reaches the bottom dead center (i.e. at a position corresponding to 180°C RK) or otherwise close to this position (e.g. at ±30°C RK, preferably at ±20°C RK and more preferably at ±10°C RK) after the air is admitted into the cylinder. This measurement is made when the intake 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 this value is minimum or when this value starts to increase again.

[0051] While the intake valve is still closed, a second pressure measurement is taken just before the overlap phase (value MAP_UP). This second measurement is usually taken because this pressure is fairly close to atmospheric pressure, and it is known to use measurements of this pressure as a function of load and speed conditions to perform training related to atmospheric pressure and obtain a good estimate of atmospheric pressure. Atmospheric pressure is referred to as AMP in the following. Since atmospheric pressure varies very little (varies with altitude), AMP is usually estimated periodically when predetermined conditions are met (e.g., avoiding estimates at low loads or at high speeds).

[0052] Usually, the value MAP is used to calculate the intake air flow, since this is the vacuum created in the intake chamber by the air entering the combustion chamber and therefore characterizes the amount of air entering the combustion chamber. This value is then corrected by the atmospheric pressure, which affects the way the inlet chamber is filled with air through the throttle housing. The following quotient is then calculated:

[0053] PQ_AMP=MAP / AMP

[0054] It is known to use two-dimensional cartography (where the input variables are, on the one hand, the engine speed N and, on the other hand, the quotient PQ_AMP) to determine a value which is multiplied by the atmospheric pressure AMP to obtain the first air flow: deb1. The latter is thus obtained by the function g:

[0055] deb1=g(N,PQ_AMP)*AMP

[0056] The value deb1 is then preferably corrected with a coefficient K which is a function of the air temperature (TA) and / or the engine temperature (TM) to obtain the desired flow rate: DEB.

[0057] This method of determining the air flow into the cylinder leads to dispersion in certain engine configurations and under certain conditions, such as Figure 2 This figure shows a curve in a reference frame, where the value of PQ_AMP is on the X-axis and the flow rate obtained using this quotient is on the Y-axis.

[0058] like Figure 2 As shown in , a small change in PQ_AMP (i.e. a small change in the measured pressure value MAP, for example 1%) for some values ​​of PQ_AMP results in a much larger change in the calculated air flow, ranging up to 10% or 12% in the example given. This causes instability in the air flow values ​​obtained under certain conditions.

[0059] Therefore, it is proposed herein to determine the air flow in a different manner when the conditions causing such instability are met. Therefore, another method for determining the air flow into the cylinder when the engine is operating at low load is described below.

[0060] There are different ways to define low engine load. In a known manner, for the electronic control of the engine, a set point torque is determined and used to set up a command to obtain the desired torque output. If the set point torque is less than a given value (e.g. a certain percentage of the maximum torque that can be supplied by the engine), the engine can be considered to be operating at a low load. For example, if the set point torque is less than 50% of the maximum torque, the engine can be considered to be operating at a low load. Another limit (e.g. between 25% and 60%) can also be envisaged.

[0061] It is also possible to define a load limit given by the opening value TPS of the throttle valve regulating the air intake for the engine speed N. This makes it possible to determine a two-entry table (N and TPS) indicating the load (set point torque) corresponding to the throttle valve opening TPS at the speed N, or to define a function f giving the limiting throttle valve opening as a function of the speed N, so that when the throttle valve opening TPS is less than or equal to this limiting throttle valve opening f(N), the engine can be considered to be operating at a low load.

[0062] Under low load conditions, it is proposed to determine a pressure quotient which no longer depends essentially on the vacuum measured in the vacuum chamber as a function of the atmospheric pressure, but takes into account the pressure change when the intake chamber is filled, also taking the atmospheric pressure into account. This pressure change is proportional to the amount of air that fills the intake chamber and is then transferred to the combustion chamber.

[0063] Therefore, it is proposed to obtain the following quotient:

[0064] PQ_LL=(MAP_UP-MAP) / (AMP-MAP)

[0065] The function h then uses this quotient PQ_LL and the engine speed to give the flow value deb2:

[0066] deb2=h(N,PQ_LL)

[0067] The value deb2 is then preferably corrected with a coefficient K which is a function of the air temperature (TA) and / or the engine temperature (TM) to obtain the desired flow rate: DEB.

[0068] Figure 3 is corresponding to Figure 2 , but using the coefficient PQ_LL. This coefficient is a combination derived from the 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 in most cases almost unchanged (compared to the value of this coefficient obtained using the exact value). It should be noted here that the curve obtained is essentially a straight line with a relatively shallow slope, so that the flow rate deb2 or DEB varies essentially linearly with PQ_LL, that is, a small change in PQ_LL causes a change in the determined flow rate in essentially the same proportion. It has been found that using the coefficient PQ_LL, if the error in the pressure measurement is approximately 1% (or x%), the error in the determined flow rate tends to be less than 1% (or x%) compared to the actual flow rate.

[0069] Figure 4 is a logic diagram outlining a preferred embodiment of the method as described above.

[0070] 180° BTDC: MAP

[0071] At approximately 180° C. RK, which corresponds to combustion top dead center of the cylinder in question, a pressure measurement in the intake chamber is taken and gives a first measured pressure value MAP.

[0072] 300°ATDC: MAP_UP

[0073] At about 300°C RK after combustion top dead center, the intake chamber has been able to refill with fresh air and the pressure therein 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 valve is located. The acquired measurement gives a second measured pressure value MAP_UP.

[0074] As indicated above, the values ​​of 180° C. RK and 300° C. RK are indicative data depending on the engine and are not limiting but merely illustrative.

[0075] As indicated above, the determination of the atmospheric pressure AMP is performed when the conditions are favorable for doing so. This pressure is usually not determined at each engine cycle, since this pressure is an external reference that changes (very) slowly compared to other values ​​used to regulate the engine. The pressure quotient PQ_AMP is determined using this atmospheric pressure value AMP, which has been stored or potentially updated, for example after measuring the pressure MAP_UP:

[0076] PQ_AMP=MAP / AMP

[0077] The limit opening value f(N) of the air supply is determined using a known reference N corresponding to the engine speed, which is measured continuously. If the current throttle opening value TPS is less than the limit value f(N), the engine is considered to be operating at low load. Therefore, TPS is compared with f(N):

[0078] TPS<=f(N)?

[0079] If TPS is less than or equal to the limit value (response 1), the engine is operated at low load, and the quotient PQ_LL is calculated:

[0080] PQ_LL=(MAP_UP-MAP) / (AMP-MAP)

[0081] This quotient of the pressure derivative in the plotted intake chamber is then used with the engine speed value to determine:

[0082] h(N,PQ_LL)

[0083] Wherein h is a function for determining the air flow rate using the engine speed N and the quotient PQ_LL.

[0084] On the other hand, if the TPS is greater than the value f(N), the engine is considered to be operating at normal or high load, and the flow calculation is performed using the ratio given by the function g:

[0085] g(N,PQ_AMP)

[0086] By multiplying this ratio by the atmospheric pressure AMP, which is already included in the logic diagram, the air flow rate is obtained.

[0087] Therefore, two parallel approaches are used to obtain a value corresponding to the air flow, depending on whether the engine is operating at low load or not. This flow value is preferably corrected with a factor K, which depends on the air temperature TA and / or the engine temperature TM.

[0088] After correction, the expected value is obtained:

[0089] DEB

[0090] The amount of air entering the cylinder in question.

[0091] In a variant embodiment, it is proposed to measure the air flow using both function g and function h. This then generates, for the same pressure measurement under the same conditions (engine speed, atmospheric pressure, etc.), two flow values: DEB_g and DEB_h.

[0092] These two flow values ​​are naturally different, but should generally be close to each other since they correspond to the same air flow into the engine.

[0093] These flow values ​​can be compared in different ways.

[0094] For example, the larger of these values ​​can be divided by the smaller:

[0095] MAX(DEB_g;DEB_h) / MIN(DEB_g;DEB_h).

[0096] For example, if the coefficient exceeds a value of 1.05 (ie, 5%), an alarm may be generated.

[0097] You can also compare the absolute difference between two values ​​to the maximum or minimum of the two values:

[0098] |DEB_g–DEB_h| / MIN(DEB_g;DEB_h)or

[0099] |DEB_g–DEB_h| / MAX(DEB_g;DEB_h)

[0100] If the first or the second of these coefficients exceeds 0.05 (ie 5%), an alarm may be generated, for example.

[0101] Those skilled in the art are aware of different ways to make a relative comparison between two values.

[0102] If the values ​​differ too far from each other and trigger an alarm, a fault such as camshaft drift can be diagnosed. This is used to detect dispersion from one engine to another.

[0103] Industrial Applications

[0104] The technical solution can be applied in particular to engine control in order to improve the precision of such control.

[0105] The proposed method and the corresponding means for implementing the method improve the determination of the air flow into the engine at low loads. This makes it possible to optimize fuel consumption and limit pollutant emissions.

[0106] For measurements taken at low loads, the proposed solution has the advantage of being insensitive to offset measurements of the pressure sensor, since the coefficients used are those of two pressure values ​​at a time.

[0107] Furthermore, for low loads, the quotient used ensures (compared to using the quotient for normal or high loads):

[0108] - less sensitive to errors in determining atmospheric pressure,

[0109] - less sensitivity to changes in the engine (such as valve clearance or incorrect angular position of the engine),

[0110] -Less sensitive to combustion instabilities.

[0111] However, as indicated, this quotient is only applicable for low engine loads and for engines including one intake chamber and corresponding pressure sensor per cylinder.

[0112] The present disclosure is not limited to the embodiments presented and to the alternatives described above, which are provided by way of example only, but covers all alternatives that a person skilled in the art can envisage within the scope of the protection sought.

Claims

1. A method for determining the air flow into a cylinder of an internal combustion engine, the engine being characterized by an engine 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, comprising an intake chamber per cylinder, each intake chamber being arranged between a variable-opening air inlet and the at least one intake valve of the cylinder and additionally comprising a pressure sensor, The method is characterized in that it comprises the following steps: - measuring the pressure in the intake chamber (MAP) for the first time after the intake valve has closed; - measuring the pressure in the intake chamber a second time before the intake valve opens (MAP_UP); - determining a correction parameter (PQ_AMP) corresponding to the ratio between the first pressure measurement (MAP) and the atmospheric pressure (AMP), namely: PQ_AMP=MAP / AMP, - determining a parameter (PQ_LL) characterizing the pressure change between the first pressure measurement and the second pressure measurement as a function of the atmospheric pressure, - using said correction parameter (PQ_AMP) and said engine speed (N) to determine for the first time the air flow into said cylinder, - determining a second time the air flow into the cylinder using the parameter characterizing 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), - generating an alarm when the flow value obtained by the first determination of the air flow on the one hand and the flow value obtained by the second determination of the air flow on the other hand differ by more than a predetermined tolerance range.

2. The method according to claim 1, wherein: - during low-load engine operation, the value of the air flow into said cylinder corresponds to the value of the air flow determined using said characteristic value (PQ_LL) and said engine speed (N), - During normal load or high load operation of the engine, the value of the air flow into the cylinder corresponds to the value of the air flow determined using the correction value (PQ_AMP) and the engine speed (N).

3. The method according to any one of claims 1 and 2, characterized in that The first pressure measurement (MAP) is obtained substantially at the bottom dead center of the intake port end, ie in the range between -180°C RK and -90°C RK before the top dead center of combustion.

4. The method according to any one of claims 1 to 3, characterized in that The second pressure measurement value (MAP_UP) is acquired before the overlap point, i.e. before the intake valve and the exhaust valve open simultaneously, i.e. in the range between 270°C RK and 360°C RK after combustion top dead center, preferably in the range between 300°C RK and 330°C RK after combustion top dead center.

5. The method according to any one of claims 1 to 4, characterized in that The parameter characterizing 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 the 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.: PQ_LL=(MAP_UP-MAP) / (AMP-MAP).

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

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

8. A non-transitory computer-readable recording medium having a program recorded thereon, the program being used to implement the method according to any one of claims 1 to 7 when the program is executed by a processor, in particular an electronic control unit of an internal combustion engine.

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