EP1931868A1 - Method for estimating instantaneous speed produced by each of the cylinders of an internal combustion engine - Google Patents

Abstract

The invention concerns a method for estimating in real time the instantaneous speed produced by each of the cylinders of an internal combustion engine, based on a measurement of the instantaneous speed at the end of the engine transmission system. The method consists in constructing a physical model representing in real time the dynamics of the transmission system based on the crankshaft angle and coefficients of a serial Fourier decomposition of the instantaneous speed produced by each of the cylinders; in determining in real time said coefficients based on a coupling between the model and an adaptive type non-linear estimator; deducing therefrom said coefficients of the instantaneous speed produced by each of the cylinders. The average torque produced by each cylinder may also be deduced therefrom. The invention is applicable to engine controls.

Description

METHOD OF ESTIMATING THE INSTANT REGIME PRODUCED BY EACH OF THE CYLINDERS OF AN INTERNAL COMBUSTION ENGINE

The present invention relates to a method for estimating in real time the instantaneous speed produced by each cylinder of an internal combustion engine from the instantaneous speed sensor located at the end of the transmission.

The knowledge of the instantaneous regime for each cylinder makes it possible to estimate the average torque produced by each cylinder.

STATE OF THE ART Estimating the average torque produced by each cylinder is important for all vehicles, whether they are petrol engines or diesel engines. In the first case, it conditions a good combustion of the mixture when the richness is close to one, and therefore sensitive to cylinder-to-cylinder difference problems. In the second case, the interest of the knowledge of the couple allows a rebalancing to obtain an optimum operation. In particular, catalysts using a NOx trap lose their effectiveness over time. In order to return to optimum efficiency, the torque of each of the cylinders must be kept identical for a few seconds, then return to normal operation at a lean mixture. The DeNOx catalysis depollution therefore requires precise control of the cylinder-by-cylinder torque.

To do this, an instantaneous speed sensor is placed at the end of the transmission. This measurement is very distorted by the transmission and is noisy. In order to control in a more precise way, and especially individual, the injection of the masses of fuel in the cylinders, a reconstruction of the cylinder to cylinder torque is indispensable. The implementation of a digital couplometer under each cylinder is unthinkable on vehicle given their cost. The method according to the invention proposes to define an estimator operating from the measurement at the end of the transmission chain to estimate the instantaneous speed under each of the cylinders.

The method of the invention relates to a method for estimating in real time the instantaneous speed produced by each of the cylinders of an internal combustion engine comprising at least one transmission system connected to the cylinders and a sensor that realizes in real time. a measurement (x _} ) of the instantaneous speed at the end of said transmission system. The method comprises the following steps: a) constructing a physical model representing in real time the dynamics of said transmission system as a function of: said measurement (xj), coefficients of a Fourier series decomposition of said instantaneous regime produced by each cylinders, and as a function of damping and a natural frequency characterizing said transmission system; b) the coefficients of said Fourier series decomposition are determined in real time by coupling said model with an adaptive type nonlinear estimator; c) real time estimation of the instantaneous regime produced by each of the rolls, from said Fourier coefficients.

We can also estimate in real time the average torque of each of the cylinders from the estimation of these coefficients.

The method according to the invention can be applied to an engine control to adapt the fuel masses injected into each of the cylinders, in order to adjust the average torque produced by each of the cylinders. Other characteristics and advantages of the method according to the invention will appear on reading the following description of nonlimiting examples of embodiments, with reference to the appended figures and described below.

Brief presentation of the figures

- Figure 1 illustrates the estimation of the instantaneous speed under the cylinders by the method according to the invention, on an operating point of 1250tr / min average load.

- Figure 2 illustrates the estimation of the average cylinder to cylinder torque by the method according to the invention, on an operating point of 1500tr / min.

Detailed description of the method

The method according to the invention makes it possible to estimate the instantaneous speed produced by each of the cylinders of an internal combustion engine comprising at least one transmission system connected to the cylinders. At the end of this transmission system, a sensor realizes a measurement of the instantaneous speed in real time. This signal is noted Xu A measurement of the instantaneous speed under the cylinders deformed by the transmission shaft is therefore achieved. The first step of the invention is therefore to "reverse" the effects of the transmission to obtain the relevant information, that is to say the instantaneous regime produced by each of the cylinders. This relevant information is a periodic signal that we note Xo-

The method consists mainly of the following four steps:

1-we establish, in an angular scale (that is to say according to the crank angle and not time), a physical model representing in real time the dynamics of the transmission system;

2- the instantaneous regime produced by each of the cylinders is characterized by quasi-invariant parameters over time, such as the coefficients of its Fourier decomposition;

3- we couple the physical model with a nonlinear estimator of adaptive type; 4-real time estimation of the instantaneous regime produced by each of the cylinders from the adaptive type nonlinear estimator.

1- Physical model of the dynamics of the transmission system

To estimate the signal Xo, that is to say the instantaneous regime under the cylinders, a physical model of the dynamics of the transmission system is first defined. To do this, we consider that this system behaves like a system of the second order which consists of two parameters: ω: the natural frequency of the transmission in the rotating repository

ζ: the damping of the transmission

Thus, and placing itself in the angular scale, the dynamics of the transmission shaft is written:

d ² (X ₁ - x ₀ ) _Έ - d (x _x -x ₀ ) _ ₂

- ξω da ² da y

with: xi: the instantaneous regime at the end of the transmission chain: the measure (y)

XQ: the instantaneous speed under the cylinders: the unknown ω: the natural frequency of the transmission system in the rotating reference system

ζ: the damping of the transmission system

a: the crankshaft angle of the transmission system A variable change can be made by asking:

The instantaneous regime under cylinders xo is periodic so w _Q too. The dynamics can be rewritten in the following form: with:

dx _x

X = \ X, da

C = [I 0]

This equation (2) constitutes the physical model representing in real time the dynamics of the transmission system. An estimation of the signal W ₀ makes it possible to determine an estimate of the signal XQ from equation (1).

2- Characterization of the signal xn by quasi-invariant parameters over time One seeks to estimate, from this physical model and from the measure y (equal to xj), the signal XQ, that is to say the regime instantaneous produced by each of the cylinders. To perform this estimation in real time, the method according to the invention characterizes this signal XQ by quasi-invariant parameters over time. In other words, the signal xo is defined using parameters which, at a given moment, are constants. To do this, we exploit the fact that the Xo signal is mechanically periodic. Thus, instead of making an estimate of the highly variable signal XQ, it is possible to estimate the Fourier coefficients of this signal. It is also possible to use all the parameters making it possible to describe the signal Xo in relation to its periodic character. The Fourier coefficient decomposition of the signal XQ, developed in complex for the clarity of the exposition, is written as follows:

The _dj represent the 2n + l Fourier coefficients of the decomposition of the signal XQ. A signal is thus defined translating the instantaneous regime Xo, as a function of the invariant parameters _jt over time.

To estimate the parameters _d, we can again use the variable change W ₀ and use the physical model described by the system (2). The signal W ₀ is also mechanically periodic, and its decomposition in Fourier coefficients, developed in complex for the clarity of the exposition, is written as follows:

The C _j represent the 2n + \ Fourier coefficients.

The estimation of these coefficients c, - thus makes it possible to estimate the Fourier coefficient decomposition of the signal XQ and thus also of the signal xo itself. By using only a finite number of harmonics ([- n; + ']), the physical model representing in real time the dynamics of the transmission system is then written:

3- Coupling with a nonlinear estimator of adaptive type

From the physical model described by the system (4), a non-linear adaptive-type estimator is defined, on the one hand, a term related to the dynamic and, on the other hand, a correction term:

with: x: x estimator

: Estimator c _j

L: a matrix to calibrate

Lj: matrices to be calibrated A choice of matrices L and L _j ensuring the convergence of the estimator is

The system of equations (5) represents an adaptive-type non-linear estimator for estimating the coefficients c _/ of the Fourier coefficient decomposition of the signal W ₀ .

This estimator (5) was constructed from the variable change w ₀ , but it is obvious that in the same way it is possible to construct an adaptive-type nonlinear estimator directly from XQ.

4 - Real-time estimation of the instantaneous regime produced by each of the cylinders It is then estimated from the estimate c _y . coefficients C _j the instantaneous regime produced by each cylinder XQ.

The estimator (5) makes it possible to reconstruct W ₀ through its Fourier coefficients Cj. The objective is to reconstruct XQ. By expression of w ₀ given by Equation (1), expresses the coefficients d _j basis of the coefficients c, -:

j _ ω ² - (j.ω) ² - ijω.ξ.ω

Y / e [- «,«] (6) ^{J ~} (W- (J. Ωff + (j.ω4 Zôf ^'Ci We thus obtain the expression of the instantaneous regime produced by each cylinder, using equations (3) and (6), and the coefficients of its Fourier decomposition by equation (6).

Estimation of the average torque produced by each cylinder

According to the invention, it is possible to provide an estimate of the average torque produced by each cylinder from the estimate of the instantaneous regime produced by each cylinder (xo) and more precisely from the estimate of its Fourier decomposition in coefficients dj.

The knowledge of the average torque produced by each cylinder is a fundamental and relevant information for the estimation of the combustion; it is the image of the combustion that the engine sees.

The previous estimator (5) allows us to estimate the signal of the regime under the cylinders but also its Fourier decomposition. However, the more torque is important the greater the excitement on the tree. In this sense it is possible to correlate the torque produced by the cylinder and the Fourier coefficients of the decomposition of the instantaneous regime signal (XQ).

In general terms, it is therefore possible to identify a function φ, which makes it possible to determine the PMI (Average Indicated Pressure) or, equivalently, the average torque from the coefficients dj:

φ: R ^{2n + ι} → R {d _j } → PMI

This function φ can be a polynomial function. It can be determined empirically from test. For example we can choose the following function φ:

with φ ₀ a constant to be calibrated according to the engine speed used using correlations with the engine bench measurements. This calibration can be done at from a tabulation, resulting from a linear optimization consisting of adjusting the value of φ ₀ so that the estimates are as close as possible to the engine parameters (parameters allowing the calibration of the engine and supplied by the manufacturer).

Results

FIG. 1 illustrates the estimation (R _es t) of the instantaneous speed Xo under the rolls from the estimator according to the invention (5) previously described on an operating point at 1250rpm average load. Figure 1 also illustrates the reference instantaneous engine speed R _ref (calculated from the cylinder pressure measurements on the test bench). We observe a very good estimate of the signal.

FIG. 2 illustrates the estimation (PMI _est ) of the cylinder-to-cylinder torque on an operating point at 1500 rpm, from the estimator according to the invention (5) and from a function φ defined by the equation ( 7). Figure 2 also illustrates the average reference torque (PMI _re f) (calculated from cylinder pressure measurements on the engine test bench). We observe a very good estimate of the signal.

The adaptive filter thus produced is efficient, and above all does not require any additional adjustment in the case of change of the operating point. No identification phase is necessary, only a measurement and model noise adjustment must be carried out, once and for all A motor control can thus, from the reconstructed pairs, adapt the fuel masses injected into each of the cylinders so that the pairs are balanced in all the cylinders.

The interest of an estimate of the instantaneous speed produced by each cylinder and the estimate of the average cylinder-to-cylinder torque are numerous: - reduction of the polluting emissions; improvement of the driving pleasure (regularization of the delivered torque);

- reduction of fuel consumption;

- diagnosis of the injection system (detection of the drift of an injector or the failure of the injection system).

Claims

1) Method for estimating in real time the instantaneous speed produced by each of the cylinders of an internal combustion engine comprising at least one system 4e transmission connected to the cylinders and a sensor which realizes a measurement (xj) of the instantaneous speed in end of said transmission system, characterized in that it comprises the following steps: a) a physical model is constructed representing in real time the dynamics of said transmission system as a function of: the crankshaft angle, of said measurement {xi}, coefficients of a Fourier series decomposition of said instantaneous regime produced by each of the cylinders, and as a function of a damping and a natural frequency characterizing said transmission system; b) the coefficients of said Fourier series decomposition are determined in real time by coupling said model with an adaptive type nonlinear estimator; c) real time estimation of the instantaneous regime produced by each of the rolls, from said Fourier coefficients. 2) Method according to claim 1, wherein is estimated in real time the average torque of each cylinder from the estimate of said coefficients. 3) Application of the method according to the preceding claims to an engine control to adapt the fuel masses injected into each cylinder to adjust the average torque produced by each of the cylinders.