CN112943463A

CN112943463A - Method for determining camshaft position of mass-produced engine

Info

Publication number: CN112943463A
Application number: CN202011440115.4A
Authority: CN
Inventors: M·施瑙贝尔特; K·延森; B·弗兰克; M·马楚尔; J·福斯特
Original assignee: Volkswagen Automotive Co ltd
Current assignee: Volkswagen Automotive Co ltd
Priority date: 2019-12-11
Filing date: 2020-12-11
Publication date: 2021-06-11
Anticipated expiration: 2040-12-11
Also published as: CN112943463B; DE102019219278A1

Abstract

The invention relates to a method for determining the camshaft position of a mass-produced engine, wherein a reference measured value is determined at a reference engine, wherein a pressure curve is obtained using a plurality of pressure measured values in an intake and/or exhaust tract of the mass-produced engine, wherein a camshaft actual value is determined using the pressure curve (CNW_Mod). The method is improved by determining the crankshaft angle of a local extreme value of a pressure measurement of at least one mass-produced engine(s) ((

Peak), wherein the crankshaft angle depends on the extreme values of the reference engine and the determined local extreme values of the pressure measurement values of the mass-produced engine(s) ((r)

Peak) to determine the camshaft actual value (NW) of mass-produced engines_Mod)。

Description

Method for determining camshaft position of mass-produced engine

Technical Field

The invention relates to a method for determining the camshaft position of a mass-produced engine.

Background

The driving of the engine timing (motorstauerung) takes place from the crankshaft to the camshaft via, for example, a gear or a timing chain (steuerkey). The cams of the camshaft open and close the intake and exhaust valves of the cylinder block via a transmission mechanism. One working cycle of the cylinder block goes through four strokes, wherein the valve is actuated only once here, so that the camshaft runs at half the rotational speed of the crankshaft. The lifting movements of the inlet and exhaust valves have to be performed by means of the camshaft at the correct point in time and in the correct sequence. The position of the intake camshaft and the exhaust camshaft relative to the crankshaft may be changed using camshaft adjustment.

In the prior art, it is known to measure a so-called reference internal combustion engine in all operating states that occur and to store the measured values or a model scheme derived therefrom on an engine controller of a corresponding mass-produced internal combustion engine. All structurally identical, mass-produced internal combustion engines of the same structural family are operated with the generated reference data set. A deviation of the actual relative position between the camshaft and the crankshaft from the reference position in the case of mass-produced internal combustion engines leads to a deviation of the actual intake fresh gas filling from the fresh gas filling determined as a reference. The angular offset of the individual cams on the camshaft causes the same error pattern as the angular offset of the camshaft and the crankshaft. The aim is therefore to be able to adjust the rotational position of the camshafts of mass-produced intake and exhaust valves better.

It is known to provide position markers on any part of the camshaft or of the coupling element or of the crankshaft, respectively, which position markers are detected by sensors. The relative position between the crankshaft and the camshaft can thus be determined and deviations can be detected. However, only a part of the deviations is detected here, since, for example, phase angle shifts of the individual cams relative to one another during assembly or due to manufacturing tolerances cannot be detected.

The evaluation of pressure signals is known from DE 102015209665 a1 of the same kind. In this method, the valve timing (sometimes referred to as valve timing) of a mass-produced internal combustion engine is identified. Dynamic pressure fluctuations in the intake or exhaust tract of the internal combustion engine concerned are measured and a crankshaft position feedback signal is additionally obtained. From the measured pressure fluctuations and the crankshaft position feedback signal, the phase angle of the picked-up signal frequency of the measured pressure fluctuations is determined by means of a fourier transformation. The camshaft position and thus the valve timing of the internal combustion engine concerned in mass production are determined on the basis of the determined phase angle and a reference valve timing of the same signal frequency, which take into account pressure fluctuations of the reference internal combustion engine, and the model function derived therefrom. This prior art has the following disadvantages: it is costly and not cost-neutral to implement.

Disclosure of Invention

The object of the present invention is therefore to improve the method for determining the position of a camshaft.

This object is achieved by the method according to the invention.

A pressure profile is obtained using a plurality of pressure measurements in the intake and/or exhaust ports of a mass-produced engine. According to the invention, at least one crankshaft angle of a local extreme value of the pressure measurement values of the mass-produced engine is determined, wherein the actual camshaft value of the mass-produced engine is determined as a function of the extreme value of the reference engine and the determined crankshaft angle of the local extreme value of the pressure measurement values of the mass-produced engine. The necessary calculations are not costly, thereby improving the method. The determination of the pressure curve is preferably carried out with a constant crankshaft speed, but can also be carried out with an increasing or decreasing crankshaft speed.

The actual camshaft value NW _ mod is determined by the crankshaft angle of the extreme value

Peak is multiplied by a factor f and a correction factor is added to determine NW_Mod=f*

Peak + c, where the factor f and the correction factor c have been determined from reference measurements. The correction factor may take into account the physical parameter that causes the extreme value shift.

The extreme crankshaft angle is advantageously dependent on the temperature T of the intake or exhaust tract and the crankshaft speed n. The camshaft position at the maximum or minimum of the pressure curve is known by measurements at the reference engine. The position of the maximum value may depend on further factors, such as, for example, the rotational speed and the temperature, in particular the temperature of the intake manifold and/or the exhaust gas temperature and/or the temperature of the exhaust manifold. In this method, the respective temperature in the intake tract or in the exhaust tract is measured. Depending on the rotational speed and the temperature, a correction value c can be determined, the actual value of the camshaft position being determined by means of a reference model. The correction value can be given by a synthetic characteristic curve, which is derived from measurements at the reference engine.

The correction value is preferably determined by a characteristic map c = K (n, T), wherein a value of the characteristic map has been determined beforehand from reference measured values, wherein the value of the characteristic map depends on the crankshaft speed n and the temperature T of the intake and/or exhaust tract. Alternatively, the correction factors may be described by a plurality of characteristic curves or by at least one mathematical equation, for example a polynomial P (), for example c = P (T, n), c = P (n) or c = P (T).

The acquisition of the camshaft position is preferably carried out on a cylinder which is in freewheeling (sometimes referred to as deceleration operation). In coasting mode, the camshaft is set to a constant setpoint value with a steady rotational speed. The measurement in coasting mode has the advantage that the extreme values known from the reference measurement values can be measured more precisely at the mass-produced engine, since no combustion of the fuel takes place in coasting mode and pressure pulsations due to the combustion are thereby avoided.

If the actual camshaft value is stable (eingeschwungen), the pressure is measured precisely over one revolution of the camshaft, in particular on the basis of a crankshaft angle of 1 °. The pressure curve is now first obtained by obtaining a plurality of measured values in the inlet and/or outlet duct. In particular, the intake manifold pressure in the intake manifold and/or the exhaust gas backpressure in the exhaust manifold can be measured. The pressure is measured over at least one revolution of the camshaft and a plurality of pressure measurements are obtained. Such measurements are preferably performed a number of times, which has the advantage that a more robust signal is obtained.

For determining the extreme values, the measured value intervals of the pressure curve are preferably selected around the crankshaft angle for which the extreme values occur in the reference model. This makes it easy to find the extreme values in mass-produced engines.

Preferably a plurality of extreme values are evaluated, which are associated with the movements of the different cylinders. For example, extrema associated with the

cylinders

1 and 4 may be evaluated. The extreme values are in different crankshaft angles, wherein a measuring interval is selected for the first cylinder and a measuring interval is selected for the second cylinder. The average measured value interval is now formed from a plurality of measured value intervals by adding the corresponding measured values of the measured intervals and dividing by the number of measured intervals.

The actual camshaft value is then modeled by evaluating the extreme values in the pressure curve. The position of the extreme value is a measure for the actual angle of the camshaft and it can be determined by means of reference data from reference measurements at a reference engine.

The determination of the extremum is performed by signal analysis. Only from the measured values obtained can the pressure limit and the associated rotational position be determined. However, this extreme value is coarse and inaccurate, since the angle information provided only by the measured values can be disturbed by the superposition of high frequencies.

The extremum is determined by means of a mathematical equation by least squares estimation of the measured values or the average measured value in the measurement interval. The mathematical equation is preferably a polynomial, in particular a second order polynomial. Alternatively, a fourth order polynomial may be used, for example. The polynomial or the mathematical model on which it is based can be interpreted here as a filtering of the pressure signal. The angle information is improved by using a plurality of measured values around the extremum and interpolating them in the model by means of polynomials, in particular quadratic polynomials. A plurality of measured values, preferably more than 10 measured values, in particular more than 15 measured values, in particular approximately 20 measured values, are used in order to determine the coefficients of the, in particular, quadratic polynomial. A least squares estimation is performed for this purpose.

The coefficients of the polynomial may be obtained by least squares estimation. The extremum of the polynomial can be calculated by making the first derivative equal to 0. True pressure curve P: (

) In the region of the extremum, the expression is represented by a polynomial: p: (

)=w0+w1*

+w2*

²The local extremum is determined by making the first derivative equal to "0". dP/d

=0+w1+2*W2

^*Thereby obtaining

_Peak=-w1/(2*w2). From this value the actual camshaft position NW can be calculated using the above mentioned equation_Mod。

In one embodiment, to determine coefficients w0 to w2, a least squares optimization is performed, for example, by QR decomposition or Cholesky decomposition. This means conversion into a linear system of equations. In a preferred embodiment of the method, a least-squares optimization is carried out by means of orthogonal polynomials, whereby the computational effort is further minimized.

Advantageously, an average value of the deviations of the actual camshaft value from the reference value is formed. Whereby the extreme value can be determined more accurately. Preferably, the model value or the model value minus the true actual angle of the camshaft is supplied to the annular memory. The result is reliable if there are sufficient values and the variance of these values is below a threshold value. The average from the annular memory is the camshaft error of the system.

To determine the actual camshaft value of the intake camshaft, the extreme value is the maximum value and the temperature is the intake pipe temperature. The method can also be used to determine the actual value of the exhaust camshaft. Here, the extreme value is the minimum value and the temperature is the exhaust gas temperature. The minimum value can be determined here via all cylinders.

Drawings

There are several possibilities for designing and improving the method. The preferred embodiments of the invention are further explained below with the aid of the figures and the description thereof. In the drawings:

fig. 1 shows a method for determining a camshaft position in a schematic flow chart.

Detailed Description

The illustrated method may be performed not only to determine the camshaft position of the intake camshaft and/or the exhaust camshaft. Depending on the speed n and the temperature T of the inlet or outlet tract, one or more angles are determined in step 1 by means of a reference model

__{Peak_Verdacht}(

__{Peak _ suspect}) There is an extreme in the pressure curve near or at said angle. This value

__{Peak_Verdacht}Can be obtained by obtaining the equation NW_Mod=f*

+ K (nT) toward

Convert and measure NW_Ist(NW_{Practice of}) Substituting:

__{Peak_Verdacht}=(NW_Ist-K (n, T))/f. The values f and K (n, T) are determined by means of a reference model or by means of reference measurements at a reference engine. The estimation

__{Peak_Verdacht}For more rapid searching for extrema in subsequent steps.

In step 2, measured values are now selected in a certain interval (for example +/-20 degrees crankshaft angle) in the pressure curve around the extreme point. In this case, this pressure curve is repeated for each movement of the respective cylinder. It is now preferably possible to average the measured values by averaging the pressure curve associated in the first cylinder and the values of the pressure curve, for example of the fourth cylinder. The average values are now stored in a domain p-norm array (p-NormArray, sometimes referred to as a p-norm array). Obtaining local maximum or minimum measured values from the values of the domain p-norm array

_{Peak_grob}(

_{Peak _ coarse})。

In step 3, the extremum is now interpolated using the mathematical model. Polynomials, in particular quadratic polynomials, are preferably used for this purpose. The coefficients of the polynomial are obtained by least squares estimation. By forming the first derivative of the polynomial and setting this first derivative equal to "0", a more accurate value can now be obtained

_{Peak_fein}(

_{Peak _ accurate}) The more accurate value is compared in step 4 with data from a reference measurement or with a reference model.

By determining limits of mass-produced engines

_{Peak_fein}The exact position of the camshaft can now be determined by comparison with a reference measurement or a reference model of the reference engine. In step 4, the crank angle is determined by taking the extreme value

_{Peak_fein}The camshaft actual value NW _ mod (NW _ model) is determined by multiplication with the factor f and addition of a correction value, wherein the factor f and the correction value have been determined from reference measured values: NW_Mod=f*

_{Peak_fein}+c。

The correction value c is preferably obtained using a characteristic curve K (), wherein the value of the characteristic curve depends on physical parameters, more preferably on the crankshaft speed n and the temperature T of the intake and/or exhaust tract: NW_Mod=f*

_{Peak_fein}+K(n,T)。

It is now output as result NW _ mod. By this correction of the camshaft position, the valve timing can be determined more accurately, wherein deviations of mass-produced engines from a reference engine are taken into account in a simple manner.

Preferably, the model value

_{Peak_fein}Or model value

_{Peak_fein}The true actual angle is subtracted for averaging. For this purpose, the values are supplied to the ring memory. The result is reliable if there are sufficient values in the ring memory and the variance of these values is below a threshold value. The average from the annular memory is the camshaft error of the system.

List of reference numerals

1, the method comprises the following steps: determining a temporary extremum

__{Peak_Verdacht}=(NW_Ist-K(n,T))/f

2, the method comprises the following steps: at value of

_{Peak_Verdacht}Pressure curve measured values are selected in intervals around the cylinder and the selected intervals are averaged, wherein the pressure curve domain p-norm array is associated with different cylinders for the averaged pressure curve and the crankshaft angle of the largest or smallest measured value in the acquired pressure curve of the domain p-norm array is determined

_{Peak_grob}

3, the method comprises the following steps: interpolation of the averaged pressure curve measured values by means of a mathematical model, in particular a second-order polynomial, and determination of the maximum value of the model

_{Peak_fein}

4, the method comprises the following steps: calculating model value NW of camshaft rotational position_Mod=f*

_{Peak_fein}+K(n,T)

Claims

1. Method for determining a camshaft position of a mass-produced engine, wherein a reference measured value is determined at a reference engine, wherein a pressure curve is obtained using a plurality of pressure measured values in an intake and/or exhaust tract of the mass-produced engine, wherein a camshaft actual value (NW) is determined using the pressure curve_Mod) Characterized by determining the crankshaft angle of a local extreme of the pressure measurement of at least one of said mass-produced engines: (

Peak), wherein the crankshaft angle depending on the extreme value of the reference engine and the determined local extreme value of the pressure measurement value of the mass-produced engine(s) ((r)

Peak) determining the camshaft actual value (NW) of the mass-produced engine_Mod)。

2. Method according to claim 1, characterized in that the camshaft actual value NW _ mod is determined by passing the extreme crankshaft angle(s) (n &)

Peak) is multiplied by a factor f and a correction factor is added to determine NW_Mod=f*

-Peak + c, wherein said factor f and said correction factor c have been determined from said reference measurement.

3. Method according to claim 2, characterized in that the correction value is determined by means of a combined characteristic curve c = K (n, T), wherein the value of the combined characteristic curve has been determined from the reference measured values, wherein the value of the combined characteristic curve depends on the crankshaft speed n and the temperature T of the inlet and/or outlet port.

4. Method according to any of the preceding claims, wherein the acquisition of the camshaft position is performed on a cylinder that is in freewheeling.

5. Method according to one of the preceding claims, characterized in that for determining the extreme value, a measured value interval of the pressure curve is selected around a crankshaft angle for which the extreme value occurs in the reference model.

6. Method according to any of the preceding claims, characterized in that an averaged measurement value interval is formed by a plurality of measurement value intervals, wherein the measurement value intervals are associated with different cylinders.

7. Method according to any of the preceding claims, characterized in that the extreme value is determined by means of a mathematical equation by least squares estimation of the measured values or averaged measured values.

8. Method according to the preceding claim, characterized in that the mathematical equation is a polynomial, in particular a second-order polynomial.

9. Method according to any one of the preceding claims, characterized in that the extreme crankshaft angle is made dependent on the temperature of the inlet or outlet channel and the crankshaft drive speed.

10. Method according to any one of the preceding claims, characterized in that an average value of the deviations of the camshaft actual value from the reference value is formed.

11. Method according to any of the preceding claims, characterized in that a pressure curve of constant crankshaft speed is obtained.