IMPROVED METHOD FOR ESTIMATING AIR FILLING IN A SUPERCHARGED PETROL ENGINE

Abstract

The method is of the type in which the air filling (R_CYL) of the internal combustion engine (MT) is estimated by means of an acoustic coefficient (CA) applied to a gas pressure (PR) in an air intake distributor of the engine. According to the invention, the method includes controlling the evolution of the acoustic coefficient in a transitional zone between an atmospheric zone and a supercharged zone according to a law that takes into account an opening position (PP) of a throttle body (PD) of the internal combustion engine. Fig. 3

Description

Title of the invention: IMPROVED METHOD FOR ESTIMATING THE AIR FILLING IN A SUPERCHARGED PETROL ENGINE

[0001] The invention relates generally to the control of internal combustion engines of the gasoline type. More particularly, the invention relates to an improved method for estimating the air filling of the cylinders of a supercharged gasoline internal combustion engine.

[0002] The estimation of the fresh air charge in the cylinders of a turbocharged gasoline engine is performed for a given engine speed and valve timing. The acoustic variation in the engine's air intake manifold is considered in two distinct zones, namely, an atmospheric zone and a turbocharged zone. In the prior art, the transition from one zone to the other occurs gradually depending on a pressure threshold and a pressure level in the air intake manifold.

[0003] Fig. 1 illustrates an example of a CBR curve, according to a prior art model, giving a normalised fresh air filling RN as a function of the average pressure PRa (in millibar “mb”) in the air intake distributor.

[0004] In this model, in an atmospheric zone ZA and a supercharged zone ZS of the CBR curve, the relationships between the filling RN and the mean pressure PRa are represented by straight sections whose slopes are acoustic coefficients CAA and CAS applied respectively in the zones ZA and ZS.

[0005] A transition factor FAT, varying between zero (0) and one (1) from a pressure threshold PS and as a function of the pressure PRa, determines the shape of the CBR curve in a transition zone ZT between the atmospheric zone ZA and the supercharged zone ZS. The pressure threshold PS, PS=f(RPM, CAL, PABP), is a function of the engine speed RPM, the valve timing CAL, and the pressure upstream of the throttle body of the internal combustion engine. The pressure threshold PS is given by the following equation: PS = Pini*PABP / P0, where Pini, Pini=f(RPM, CAL), is an initial pressure threshold value that is a function of the engine speed RPM and the valve timing CAL, and PO is the atmospheric pressure. The width of the transition zone DP, DP=f(RPM), is a function of the engine speed RPM. The transition factor FAT is represented by the following equality: FAT = (PRa - (Pini*PABP / P0)) / DP.

[0006] Generally, in prior art designs, several pressure thresholds in the air intake distributor must be taken into consideration, as these depend on numerous engine settings, such as those of the actuators Variable valve timing (VVT), turbocharger, exhaust enthalpy, and other factors are all taken into account. Given the large number of engine settings, this can result in a lack of robustness in prior art models for accurately accounting for all these settings, to the detriment of the accuracy of fresh air load estimation in certain engine operating conditions.

[0007] Simulations and tests carried out by the inventing entity on a turbocharged gasoline engine revealed insufficient representativeness of the physical phenomenon of intake acoustic variation by prior art models. Thus, in the atmospheric zone, the acoustics in the air intake distributor are considered invariant with respect to the position of the throttle body.

[0008] By way of illustration and with regard to the comments above, Figure 2 shows measurement readings of the evolution of the air intake acoustics EA1 as a function of the average pressure PRa (in millibars “mb”) in the air intake distributor. The evolution of the air intake acoustics EA1 is given by the following equation: EA1 = 100*(PR(FA) - PRa) / PRa, where PR(FA) is the instantaneous pressure and PRa is the average pressure in the air intake distributor when the intake valve is closed.

[0009] The measurements in [Fig. 2] were taken in a turbocharged engine with a double camshaft phaser, with a fixed engine speed of 1800 rpm. The measurement point cloud, visible in [Fig. 2], groups several measurements of EAl=f(PRa) corresponding to intake valve timing angles from +35.25 degrees to -42.75 degrees, for a lift of 1 mm.

[0010] The measurements in [Fig. 2] show the absence of a direct relationship between the evolution of the air intake acoustics EA1 and the average pressure PRa in the air intake distributor. Furthermore, in the atmospheric zone ZA, an evolution of the acoustics appears that is not taken into account by the prior art models.

[0011] It is desirable to propose an improved method not presenting the aforementioned disadvantages of the prior art, for a more precise estimation of the air filling of the cylinders of the supercharged gasoline internal combustion engine and allowing a simplification of calibration tests and a reduction in the time required to carry them out.

[0012] According to a first aspect, the invention relates to a method for estimating the air filling of the cylinders of a turbocharged gasoline internal combustion engine incorporating a throttle body in its air intake loop, the method being of the type in which the air filling is estimated by means of an acoustic coefficient applied to a gas pressure in an air intake distributor of the internal combustion engine. According to the invention, the method includes a control of the evolution of the acoustic coefficient in a transitional zone between an atmospheric zone and a supercharged zone according to a law taking into account a position of the opening of the throttle body.

[0013] According to a particular feature of the process, the control law for the evolution of the acoustic coefficient in the transient zone allows consideration of the opening position of the throttle body when it is between a maximum opening position and a minimum opening position which are defined according to an engine speed and a timing of the internal combustion engine.

[0014] According to another particular feature of the method, the control law of the evolution of the acoustic coefficient in the transient zone includes a transition factor determining this evolution as a function of the opening position of the throttle body and a timing of the internal combustion engine.

[0015] According to yet another particular feature of the process, the transition factor is determined from air intake acoustic measurements in the internal combustion engine as a function of the opening position of the throttle body for different distribution timings.

[0016] According to another aspect, the invention also relates to a computer comprising a memory storing program instructions for implementing the method as briefly described above. In a particular embodiment, the computer is an engine control computer for a vehicle.

[0017] In yet another aspect, the invention also relates to an assembly comprising a turbocharged gasoline internal combustion engine and a control unit, the internal combustion engine incorporating a throttle body in its air intake loop, wherein the control unit is a computer as described above. In yet another aspect, the invention also relates to a vehicle comprising an assembly as described above.

[0018] Other advantages and features of the present invention will become more apparent upon reading the detailed description below of a particular embodiment of the invention, with reference to the accompanying drawings, in which:

[0019] [Fig-1] [Fig.1] shows curves, according to the prior art, of the filling in fresh air of a supercharged petrol internal combustion engine as a function of the average pressure in the engine's air intake distributor and a transition factor between the so-called atmospheric zone and the so-called supercharged zone.

[0020] [Fig.2] Fig.2 represents a scatter plot of measurement readings of the evolution of the air intake acoustics in a supercharged gasoline internal combustion engine function of the average pressure in the engine air intake distributor, in accordance with the state of the art.

[0021] [Fig.3] The [Fig.3] is a block diagram of the principle relating to the implementation of the method according to the invention in a supercharged petrol internal combustion engine.

[0022] [Fig.4] Fig.4 represents a scatter plot of measurement readings of the evolution of the air intake acoustics in a supercharged petrol internal combustion engine as a function of the opening position of the throttle of the internal combustion engine, according to the method of the invention.

[0023] [Fig. 5] [Fig. 5] shows a scatter plot of several curves of a factor standardized transition for different intake valve timing angles, depending on the opening position of the internal combustion engine throttle, according to the method of the invention.

[0024] [Fig.6] Fig.6 schematically shows a control law conforming to method of the invention used for determining an acoustic coefficient applicable for calculating the estimated air filling of the internal combustion engine.

[0025] With reference to [Fig. 3], in the particular embodiment described herein, the method according to the invention is implemented in a vehicle control unit (CCM), such as an engine control unit, responsible for controlling a vehicle internal combustion engine (MT). In this embodiment, the internal combustion engine (MT) is a turbocharged, direct-injection gasoline engine.

[0026] An embedded software system SLE is contained in a MEM memory of the CCM computer and its function is the general control of the internal combustion engine MT. Data communications for the control of the internal combustion engine MT, between the embedded software system SLE and various actuators and sensors of the internal combustion engine MT, are typically carried out through a vehicle data communication network, for example a CAN bus.

[0027] The embedded software system SLE includes, in particular, software modules M0D1, M0D2, and M0D3. Software modules M0D1 and M0D2 are responsible, respectively, for implementing the fuel injection control strategy SU and the air intake loop control strategy SAA. Software module M0D3 is dedicated to calculating the estimated air filling of the internal combustion engine MT by implementing the method according to the invention. As shown in [Fig. 3], the estimated air filling information R_CYL is provided to software modules M0D1 and M0D2 for use by the SU and SAA control strategies. Software module M0D3 implements the method according to the invention by executing program code instructions using a processor (not shown) of the CCM computer.

[0028] As schematically represented in [Fig. 3], the MT internal combustion engine comprises an air intake loop essentially consisting of an air filter FA, an air flow meter DEB, a throttle body PD, a turbocharger TC, a lambda sensor SL, and exhaust gas recirculation circuits of the "high pressure" type with an EGR_HP valve and of the "low pressure" type with an EGR_BP valve. Heat exchangers ET1 and ET2 are provided for cooling the compressed air flow exiting the turbocharger TC and the exhaust gas flow exiting the EGR_BP valve, respectively.

[0029] The air filter FA filters the incoming fresh air stream AIR. The air flow meter DEB measures the flow rate of the incoming fresh air stream AIR. The turbocharger TC increases the pressure of the incoming fresh air stream AIR for air boosting. Cooling the compressed air stream by the heat exchanger ET1 allows for improved air filling of the cylinders of the internal combustion engine MT.

[0030] The PD throttle body allows the quantity of fresh air admitted into the cylinders of the MT internal combustion engine to be metered according to an opening position PP of the throttle.

[0031] According to the method of the invention, the throttle position information PP is provided to the M0D3 software module to be used for estimating the air filling R_CYL, as will become clearer later. Pressure information PR and temperature information TE in the intake manifold of the internal combustion engine MT are provided by measuring sensors and are also used for estimating the air filling R_CYL.

[0032] In the process of the invention, the estimation of the air filling R_CYL uses the following equations 1) to 3):

[0033] 1) R_CYL = MA / MO = (Mtot-MB) / M0,

[0034] 2) MB = MBres + MBrea, and

[0035] 3) Mtot = ((CA*PRa)*VCFA) / (R*TE),

[0036] in which MA is the mass of fresh air in the cylinder, Mtot is the total mass of gas in the cylinder, MO is the reference mass at normal temperature and pressure conditions for a unit volume, MB is the total mass of gas burned in the cylinder, MBres is the residual mass of burned gas in the cylinder in the absence of valve overlap, MBrea is the mass of burned gas internally re-aspirated into the cylinder with valve overlap, PRa is the average pressure in the air intake distributor, CA is an acoustic coefficient associated with the average pressure PRa, VCFA is the volume of the cylinder at the closing of the intake valve, TE is the temperature of the gases in the air intake distributor and R is a specific air constant.

[0037] According to the method of the invention, an estimate of the total mass of gas Mtot in the cylinder is first made from equality 3) to then obtain the mass of fresh air MA in the cylinder, and consequently the filling with air R_ CYL, from equality 1) and 2).

[0038] In the present invention, unlike the prior art in which the transition factor applied to the acoustic coefficient (cf. FAT, CAA and CAS in [Fig.1]) is determined as a function of a pressure threshold and the average pressure in the air intake distributor, the transition factor of the invention, designated FT, which is applied to the acoustic coefficient CA, is determined as a function of the opening position PP of the throttle valve.

[0039] With further reference to [Fig.3], the M0D3 software module dedicated to calculating the estimated air filling R_CYL includes in particular a function F30 and a function F31.

[0040] The function F30 is responsible for determining the value of the transition factor FT to be applied to the acoustic coefficient CA as a function of the throttle opening position PP. In the invention, the transition factor FT is therefore a function of the opening position PP, FT=f(PP).

[0041] The function F31 is responsible for calculating the air filling estimate R_CYL and uses for this purpose the equations 1) to 3) detailed above. The calculation of the air filling estimate R_CYL uses information provided by measuring sensors, such as the opening position PP of the throttle valve, the pressure PR and the temperature TR of the gases in the air intake distributor and the engine speed RPM, and information provided by maps according to the operating and adjustment conditions (valve timing) of the MT engine, such as the burnt masses MBres and MBrea, the VCFA volume, the reference mass MO and the constant R.

[0042] Figure 4 shows measurement readings of the evolution of the acoustics of Air intake EA2 as a function of the throttle opening position PP. The evolution of the air intake acoustics EA2 is given by the following equation: EA2 = 100*(PR(FA) - PRa) / PRa, where PR(FA) is the instantaneous pressure and PRa is the average pressure in the air intake manifold at the intake valve closing. The measurements in [Fig. 4] were taken under conditions similar to those in [Fig. 2] relating to the prior art, namely, in a turbocharged engine with a dual camshaft phaser, at a fixed engine speed of 1800 rpm. The scatter plot of measurements, visible in [Fig. 4], groups several measurements of EA2=f(PP) corresponding to intake valve timing angles from +35.25 degrees to -42.75 degrees, for a 1 mm lift.

[0043] The readings in [Fig.4] show the existence of a direct relationship between the evolution of the air intake acoustics EA2 and the opening position PP of the throttle valve and therefore validates the approach of the invention consisting of using the PP position for estimating the air filling.

[0044] With reference also to [Fig. 5], the transition factor FT applicable in the present invention is obtained here by normalizing the curves of the readings in [Fig. 4] to have a change between zero (0) and one (1) on the abscissa and ordinate. The transition factor FT is given by the following equation:

[0045] FT = [[100*(PR(FA) - PRa) / PRa] - MIN[100*(PR(FA) - PRa) / PRa]] / [MAX[100* (PR(FA) - PRa) / PRa] - MIN[100*(PR(FA) - PRa) / PRa]]

[0046] In [Fig. 5], PPn is the standardized opening position of the throttle valve. The scatter plot appearing in [Fig. 5] groups several curves FT=f(PPn, CAL) corresponding to intake valve timing angles CAL from +35.25 degrees to -42.75 degrees, for a lift of 1 mm.

[0047] A control law LC according to the method of the invention, for determining the acoustic coefficient CA, is represented in a simplified manner in [Fig. 6]. As can be seen in [Fig. 6], the control law LC essentially comprises three maps CTmin, CTmax and CTft and two calculation blocks B1 and B2.

[0048] The calculation block B1 is responsible for providing the normalized opening position PPn of the throttle valve. Block B1 receives as input the opening position PP provided by the throttle body position sensor PD and outputs the normalized opening position PPn, which varies between zero (0) and one (1). The range of PP opening position to be considered by block B1 is defined by maximum opening positions Pmax and minimum opening positions Pmin provided respectively by the CTmax and CTmin maps as a function of engine speed and valve timing CAL.

[0049] The CTft mapping provides, as a function of the normalized opening position PPn and the distribution calibration CAL, the value of the transition factor FT to be applied for the calculation of the acoustic coefficient CA by the block B2. The transition factor FT varies between zero (0) and one (1), as indicated previously.

[0050] Block B2 calculates the acoustic coefficient CA for the calculation of the air filling R_CYL using the following equality:

[0051] CA = (CAs- CAa)*FT + CAa = (CAa*Ks - CAa)*FT + CAa

[0052] in which CAa is the acoustic coefficient in the atmospheric zone, CAs is the acoustic coefficient in the supercharged zone and Ks is a proportionality coefficient between CAa and CAs.

[0053] In the atmospheric zone, the transition factor FT is equal to zero, FT=0, and the acoustic coefficient CA is equal to CAa. In the supercharged zone, the factor of The transition factor FT is equal to one, FT=1, and the acoustic coefficient CA is equal to CAs. In the transition zone, the acoustic coefficient CA is between CAa and CAs depending on the value of the transition factor FT=f(PPn, CAL).

[0054] The invention is not limited to the particular embodiment described herein by way of example. A person skilled in the art may, depending on the applications of the invention, make various modifications and variations falling within the scope of the invention's protection.

Claims

Demands

1. A method for estimating the air filling (R_CYL) of the cylinders of a supercharged gasoline internal combustion engine (MT) incorporating a throttle body (PD) in its air intake loop, said method being of the type in which said air filling (R_CYL) is estimated by means of an acoustic coefficient (CA) applied to a gas pressure (PRa) in an air intake distributor of said internal combustion engine (MT), this acoustic coefficient being the slope of a straight section representing the relationship between a normalized filling (RN) and an average pressure (Pra) in the air intake distributor, characterized in that it comprises a control of the evolution of said acoustic coefficient (CA) in a transitional zone (ZT) between a so-called atmospheric zone (ZA) and a so-called supercharged zone (ZS) according to a law (LC) taking into account an opening position (PP) of said throttle body (PD),said law (LC) for controlling the evolution of said acoustic coefficient (CA) in said transition zone (ZT) comprising a transition factor (FT) determining said evolution as a function of said opening position (PP, PPn) of said throttle body (PD) and a valve timing (CAL) of said internal combustion engine (MT), said transition factor (FT) being determined from intake air acoustic measurements (EA2) in said internal combustion engine (MT) as a function of said opening position (PP) of said throttle body (PD) for different valve timings (CAL).

2. Method according to claim 1, characterized in that said law (LC) of control of the evolution of said acoustic coefficient (CA) in said transitional zone (ZT) allows a consideration of said opening position (PP, PPn) of said throttle body (PD) when it is between a maximum opening position (Pmax) and a minimum opening position (Pmin) which are defined as a function of an engine speed (RPM) and a valve timing (CAL) of said internal combustion engine (MT).

3. Computer (CCM) comprising a memory (MEM) storing program instructions (M0D3) for the implementation of the method according to any one of claims 1 to 2.

4. Computer according to claim 3, characterized in that said computer is an engine control computer (ECC) of a vehicle.

5. Assembly comprising a supercharged petrol internal combustion engine (MT) and a control computer (CCM), said internal combustion engine (MT) incorporating a throttle body (PD) in its air intake loop, characterized in that said control computer is a computer (CCM) according to claim 3 or 4.

6. Vehicle comprising an assembly (MT, CCM) according to claim 5.

Images