GB2356053A

GB2356053A - Method for determining engine torque and applying correction

Info

Publication number: GB2356053A
Application number: GB0021101A
Authority: GB
Inventors: Manfred Homeyer; Winfried Langer
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 1999-08-30
Filing date: 2000-08-25
Publication date: 2001-05-09
Anticipated expiration: 2020-08-25
Also published as: IT1318782B1; ITMI20001907A0; ITMI20001907A1; DE19941172A1; FR2797950B1; GB0021101D0; DE19941172C2; GB2356053B; FR2797950A1; JP2001082236A

Abstract

A method of determining the actual torque produced by an internal combustion engine comprising determining a characteristic curve (1) of the rotational speed of a component of the engine, ascertaining the gas filling of a combustion chamber of an engine cylinder, calculating an initial torque and applying correction dependent on the gas filling. The gas filling is ascertained by establishing a standard characteristic curve (2) of the rotational speed of a component of the engine for a fuel to air mixture of 1:1 ( g = 1) and measuring deviations between the curves. Alternatively the gas filling may be determined from the area between the characteristic curve (1) and a line connecting the minima of that curve (see figure 2).

Description

2356053 METHOD OF DETERMINING ENGINE TORQUE The present invention relates

to a method of determining actual torque produced by an internal combustion engine.

For detection of the angular setting of a crankshaft in an internal combustion engine it is known to provide on the shaft a transmitter disc or a transmitter wheel with markings which are scanned by means of a stationary pick-up. The transmitter wheel is constructed as, for example, a gearwheel with teeth as markings at the circumference. The pick-up is, for example, an inductive pick-up, in which voltage pulses are induced by the teeth running past in each revolution of the crankshaft and of the transmitter wheel. The time spacings of the voltage pulses or of the teeth of the wheel, thus the tooth times, are measured. From the course of the measured tooth times, the actual characteristic curve of the course of the rotational speed (n) of the crankshaft is then ascertained from the reciprocal value of the product of the total number (Z) of the teeth of the wheel and the measured tooth time (tz), (n = 1 / (tz Z)). The rotational speed of the crankshaft can be readily converted into the angular speed (Omega) of the crankshaft (omega = 2 pi n).

In a subsequent evaluating step, the course of the actual torque produced by the engine is ascertained either from the measured tooth times, from the actual characteristic of the course of the rotational speed of the crankshaft or from the angular speed of the crankshaft. The actual torque of the internal combustion engine is passed on to a central control unit of the engine for optimisation of the performance, noise output and exhaust emissions of the engine. The actual torque can also be utilised for regulation of power or torque, regulation of the dynamic range of travel or monitoring of the torque.

In the case of conventional internal combustion engines which are operated at lambda = 1, the fuel-air mixture is in the ratio of 1:1 in the combustion chambers. Engines of more recent mode of construction are operated with increasingly leaner mixtures (lambda > 1) or with exhaust gas return (AGR) for reduction in fuel consumption, exhaust gas emissions and/or noise output of the engine. The fuel-air mixture in such an engine can be made leaner as far as a ratio of 1:5 (lambda = 5). In future, even leaner operation of engines is likely to be possible. The additionally present air or exhaust gas in the combustion chamber in the case of an operation of the engine at lambda > I leads to a change in the tooth times, the course of the rotational speed and thereby also the angular speed of the 2 crankshaft without actually leading to a different actual torque produced by the engine. In particular, due to the higher gas filling of the combustion chamber during the compression phase a braking of the crankshaft and, during the subsequent expansion phase, an acceleration of the crankshaft occur. The braking of the crankshaft manifests itself as an earlier rise of the tooth times and the acceleration of the crankshaft as an earlier reduction in the tooth times.

Due to the gas filling during the operation of the engine at lambda > 1 or with exhaust gas return, the actual torque produced by the engine and ascertained is falsified. For this reason, the gas filling of the combustion chamber must be ascertained and the ascertained actual torque of the engine must be corrected in dependence on the gas filling. It is known to ascertain the gas filling in a combustion chamber by way of an air mass sensor.

There is, however, a need for a method of determining engine torque with ascertaining of the gas filling in a combustion chamber of an engine without resort to additional measuring means.

Accordingly to a first aspect of the invention there is provided a method of determining torque produced by an internal combustion engine, comprising the steps of recording the actual characteristic of the course of the rotational speed of the engine crankshaft, ascertaining the gas filling in a combustion chamber of a cylinder of the engine, ascertaining actual torque by evaluation of the actual characteristic of the course of the rotational speed and correcting the actual torque in dependence on the ascertained gas filling, wherein for ascertaining the gas filling in the combustion chamber a standard characteristic of the course of the rotational speed is fixed for the operation of the engine at lambda = 1, the standard characteristic is amplified in a working stroke of the cylinder so that the extremes of the standard characteristic and the actual characteristic have the same rotational value, a first area is ascertained between the standard characteristic and the actual characteristic in the first half of the stroke, a second area is ascertained between the standard characteristic and the actual characteristic in the second half of the stroke, a measure for the gas filling is ascertained from the sum of the first area and the second area or from the sum of certain parts of the first area and the second area and the gas filling in the combustion chamber is ascertained from the measure for the gas filling.

3 According to a second aspect of the invention there is provided a method of determining torque produced by an internal combustion engine, comprising the steps of recording the actual characteristic of the course of the rotational speed of the engine crankshaft, ascertaining the gas filling in a combustion chamber of a cylinder of the engine, ascertaining actual torque by evaluation of the actual characteristic of the course of the rotational speed and correcting the actual torque in dependence on the ascertained gas filling, wherein for ascertaining the gas filling in the combustion chamber a base line is ascertained as connecting line of the minima of the actual characteristic, a first area is ascertained between the actual characteristic of the rotational speed and the base line in the first half of a working stroke of the cylinder, a second area is ascertained between the actual characteristic of the rotational speed and the base line in the second half of the stroke, a measure for the gas filling is ascertained from one of the two areas, from the difference between the first area and the second area or from the ratio of the first area to the second area and the gas filling in the combustion chamber is ascertained from the measure.

Since the course of the rotational speed of the crankshaft and from this in turn the angular speed of the crankshaft can be ascertained from the tooth times, it is self-evident that the method can be carried out with, instead of the rotational speed of the crankshaft, directly on the basis of the tooth times or alternatively the angular speed of the crankshaft. Furthermore, it is feasible to carry out the method with the aid of any other desired characteristic which can be derived from the actual characteristic of the course of the rotational speed of the crankshaft.

An inductive rotational speed transmitter can be used for ascertaining crankshaft speed. The rotational speed transmitter can comprise a transmitter gearwheel associated with the crankshaft and a stationary inductive pick-up. On a rotation of the crankshaft and the gearwheel, voltage pulses are induced in the pick-up by the teeth. The time spacings of the voltage pulses or of the teeth, thus the so-called tooth times, are measured. The course of the rotational speed of the crankshaft can then be ascertained from the tooth times and the total number of the teeth.

The deviations of the actual characteristic of the course of the rotational speed relative to the standard characteristic, which is recorded for lambda = 1, can be utilised for ascertaining the gas filling of the combustion chamber, since the actual characteristic for 4 lambda > 1 departs significantly from the standard characteristic. The deviations of the actual from the standard characteristic can be ascertained in different ways.

During a double rotation of the crankshaft, each of the cylinders of the engine performs one working stroke. Accordingly, the number of the teeth of the transmitter gearwheel comprehended by one working stroke results from the quotient of twice the number of teeth of the transmitter gearwheel and the number of the cylinders of the engine. In the case of a 60-2 gearwheel, which has 60 teeth at its circumference of which two teeth are imaginary, thus not actually present, and form a gap, it results for a 4-cylinder internal combustion engine that the working stroke of a cylinder covers thirty teeth (260 teeth/4 cylinders = 30).

In the case of the first method, a standard characteristic of the course of the rotational speed is initially determined for the operation of the engine for lambda = 1. The gas filling of the combustion chamber is then ascertained from the deviations of the actual and standard characteristics. For this purpose, the standard characteristic in a working stroke of the cylinder is amplified so that the extremes of the standard characteristic and of the actual characteristic have the same rotational speed values.

A first area between the standard and actual characteristics in the first half of the working stroke and a second area between these characteristics in the second half of the stroke are then ascertained. In the case of the afore-mentioned example, the first half of the stroke thus corresponds with teeth 1 to 15 and the second half of the stroke with teeth 16 to 30. The first tooth is to be applied at the point of the lowest speed, thus at the top dead centre (TDC) of the cylinder.

In the case of the second method, a base line is initially determined from the minima of the actual characteristic. A first area is then ascertained between the actual characteristic and the base line in the first half of the working stroke and a second area is ascertained between the actual characteristic and the base line in the second half of the stroke.

The two areas in either version of the method can be any desired interval within the first half or the second half of the working stroke. It is, however, important for a reliable and exact ascertaining of the gas filling of the combustion chamber for the first and second areas within a working stroke to always be considered in the same intervals.

A measure for the gas filling is then ascertained from the difference between the first area or from the ratio of the first area to the second area. Finally, the gas filling is ascertained from the measure.

The actual torque produced by the engine and ascertained by the method is corrected in dependence on the ascertained gas filling. For correction of the ascertained actual torque, the measure can, however, be utilised directly without previously ascertaining the gas filling. It is also feasible to employ any desired other magnitude, which can be derived from the measure for the gas filling, for correction of the ascertained actual torque.

By means of a method exemplifying the invention, a measure for the gas filling of the combustion chamber can be ascertained in simple manner and without substantial computing effort. The ascertained actual torque can then be corrected either directly with the aid of the measure for the gas filling or indirectly with the aid of the gas filling. As a result, the accuracy of determining the actual torque can be significantly improved and the use of additional measuring means for ascertaining gas filling is not necessary.

In an advantageous development, the actual characteristic is corrected for calculable influencing magnitudes, at least for the oscillating masses, before the ascertaining of the gas filling.

In one preferred example, the first area comprehends the entire area between the standard characteristic and the actual characteristic or between the actual characteristic and the base line in the first half of the working stroke.

In another preferred example, the first area comprehends the area between the standard characteristic and the actual characteristic or between the actual characteristic and the base line in the first half of the working stroke in a specific interval.

Similarly, the second area can comprehend the entire area between the standard characteristic and the actual characteristic or between the actual charactedstic and the base line in the second half of the working stroke. Alternatively, the second area can comprehend the area between the standard characteristic and the actual characteristic or 6 between the actual characteristic and the base line in the second half of the working stroke in a specific interval.

For preference, the gas filling in the combustion chamber is ascertained from the product of the measure for the gas filling and a proportionality factor, thus from the equation:

m-L = A k-P wherein m-L is the gas filling, A is the measure for the gas filling and k_p is the proportionality factor.

Alternatively, the gas filling can be ascertained from the product of the measure for the gas filling and a characteristic which is dependent on certain parameters of the engine, for example rotational speed.

Advantageously, the proportionality factor or the characteristic is ascertained before the actual determination of the actual torque. For this purpose, the actual value of the gas filling in the combustion chamber is measured in other ways. The proportionality factor or the characteristic can be ascertained from the quotient of the measured actual value of the gas filling and the ascertained measure for the gas filling with an internal combustion engine having the least possible tolerances, the proportionality factor thus resulting from the equation k_p = m_L-ist / A, wherein k_p is the proportionality factor, m-L-ist is the otherwise measured actual value for the gas filling and A is the ascertained measure for the gas filling. For the measurement of the actual value of the gas filling, the engine can be operated actually or in simulated manner.

The proportionality factor determination is carried out before performance of the method for ascertaining the actual torque and is stored in suitable manner. The stored proportionality factor or characteristic can then be utilised for the ascertaining of the gas filling. The ascertaining of the proportionality factor must be carried out for each type of 7 engine. The ascertained proportionality factor or the ascertained characteristic can then be used for all engines of that type.

It is feasible to obtain the proportionality factor by simulation. Preferably, however, the proportionality factor is ascertained empirically on an engine test bed. On an engine test bed, realistic measurement results close to the practice can be achieved, so that the results can include such factors as do not usually enter into a simulation. On the other hand, the interference factors acting on an engine, in particular tolerances, can be reduced on an engine test bed and compensation can be made for their influence on the measurement results.

The method can be used for lean-burn or stratified charge engines for ascertaining the actual torque. These kinds of engines are operated with lambda > 1. The gas filling in the combustion chamber of these engines can lead to errors in the ascertaining of the actual torque, when this is based on evaluation of the course of the rotational speed of the crankshaft. These errors are compensated for in simple manner in a method exemplifying the invention.

Preferred examples of the method of the present invention will now be more particularly described with reference to the accompanying drawings, in which:

Fig. 1 is a diagram showing a standard characteristic and an actual characteristic of the course of the rotational speed of a crankshaft of an internal combustion engine and illustrating an aspect of a first method exemplifying the invention; and Fig. 2 is a diagram showing an actual characteristic of the course of the rotational speed of the engine crankshaft and illustrating an aspect of a second method exemplifying the invention.

Referring now to the drawings, Figs. 1 and 2 depict aspects in the determination of the gas filing of the combustion chamber of an internal combustion engine by two alternative procedures. The ascertained gas filling is then utilised for correction of the determined actual torque produced by the engine, the torque being determined by evaluation of the course of the rotational speed of the crankshaft.

8 In the case of a method exemplifying the invention, an inductive rotational speed transmitter is used for ascertaining the actual torque produced by the engine. The rotational speed transmitter comprises a transmitter gearwheel associated with the engine crankshaft and a stationary inductive pick-up. On a rotation of the crankshaft and the gearwheel, voltage pulses are induced in the pick-up by the gearwheel teeth. The time spacings of the voltage pulses or of the teeth of the transmitter gearwheel, thus, the tooth tirnes tz, are measured. From the tooth times tz and the total number Z of the teeth of the gearwheel, the course of the rotational speed n of the crankshaft can then be ascertained (n = 1 / (tz Z)). The rotational speed n of the crankshaft can readily be converted into the angular speed omega of the crankshaft (omega = 2 pi + n). The actual torque M - ist produced by the engine is determined by evaluation of the tooth times tz, the crankshaft rotational speed n or the crankshaft angular speed omega.

In the case of a conventional engine operated at lambda = 1, an air-fuel mixture in a ratio of 1:1 is disposed in the combustion chamber of a cylinder of the engine. However, internal combustion engines of newer mode of construction are, for reduction in fuel consumption, exhaust gas emissions and/or combustion noise output, operated with increasingly leaner mixtures, i.e. with lambda > 1, or with exhaust gas return (AGR). The fuel-air mixture can in such an engine be leaned up to a ratio of 1:5 (lambda = 5). The air or exhaust gas additionally present in the combustion chamber when the engine is operated at lambda > 1 leads to a change in the tooth times tz, the course of the rotational speed n and thereby also the angular speed omega of the crankshaft without actually leading to a different actual torque M-ist produced by the engine. In particular, due to the higher gas filling of the combustion chamber during the compression phase, braking of the crankshaft takes place during the compression phase and acceleration of the crankshaft during the subsequent expansion phase. The braking of the crankshaft manifests itself in an earlier rise of the tooth times tz and the acceleration of the crankshaft in an earlier reduction of the tooth times tz.

Due to the gas filling in the case of an engine operated with lambda > 1, the ascertained actual torque is falsified. For this reason, the gas filling of the combustion chamber must be ascertained and the ascertained actual torque M-ist must be corrected in dependence on the gas filling. In the case of the examples illustrated in Figs. 1 and 2, the characteristic of the tooth times tz is evaluated for ascertaining the gas filling. The method is, however, 9 readily performable by evaluation of the characteristic of other magnitudes derived from the tooth times tz, for example the rotational speed n or the angular speed omega of the crankshaft.

In the case of a method exemplifying the invention, an actual characteristic tz(z) of the tooth times tz is entered as a function of the individual teeth z of the transmitter gearwheel (curve 1 in Figs. 1 and 2). In order to ascertain the gas filling of the combustion chamber, the deviations of the actual characteristic tz(z) relative to a standard characteristic tz-norm(z), which is recorded for lambda = 1 (curve 2 in Fig. 1), are ascertained. The actual characteristic 1 for lambda greater than 1 deviates significantly from the standard characteristic 2. The deviations of the characteristic 1 from the characteristic 2 can be ascertained in different ways.

During a double rotation of the crankshaft, each of the cylinders of the engine performs a working stroke. Accordingly, the number of the teeth of the transmitter gearwheel, which comprehends a working stroke of a cylinder, results from the quotient of twice the number of teeth of the gearwheel and the number of the cylinders of the engine. In the case of a 60-2 gearwheel, which has 60 teeth at its circumference, of which two teeth are constructed only in imagination, thus are not actually present, and form a gap, it results for a 4-cylinder engine that the working stroke z-hub of a cylinder embraces thirty teeth (260 teeth/4 cylinders = 30). In the examples of Figs. 1 and 2, a working stroke z-hub is considered, which goes from the tooth z = 13 to z = 43.

In the case of the first example (cf Fig. 1) the standard characteristic tz-norm(z) 2 of the tooth times tz-norm is initially determined for the operation of the engine with lambda = 1. Then, the gas filling in the combustion chamber is ascertained from the deviations of the actual characteristic tz(z) 1 of the tooth times z relative to the standard characteristic tz-norm(z) 2. For this purpose, the standard characteristic 2 of the tooth times tz in the working stroke z - hub of a cylinder of the engine is amplified so that the extremes of the characteristics 1 and 2 have the same value for the tooth time tz.

A first area F1 between the characteristics 1 and 2 is ascertained in the first half of the working stroke z - hub and a second area F2 between the characteristics in the second half of the stroke. In the illustrated examples, the first half of the working stroke thus corresponds with the teeth z = 13 to z = 28 and the second half of the stroke z-hub with the teeth z = 29 to z = 43.

In the case of the second example (cf Fig. 2), a base line, which results from the connecting line of the minima of the actual characteristic, is initially determined. Then, the first area F1 between the actual characteristic 1 and the base line is determined in the first half of the working stroke z-hub of a cylinder of the engine and a second area F2 is determined between the actual characteristic and the base line in the second half of the stroke.

In Figs. I and 2, the first area F1 and the second area F2 each comprise the entire area between the standard characteristic 2 and the actual characteristic 1, or between the actual characteristic 1 and the base line, in the respective half of the working stroke. The areas F1 and F2 can, however, be confined to any desired interval within the first half and second half of the stroke. It is, however, important for a reliable and exact ascertaining of the gas filling that always the same first and second areas F1 and F2 within the respective working stroke are considered.

A measure A for the gas filling of the combustion chamber is then ascertained from the difference between the first area F1 and the second area F2. Alternatively, the measure A for the gas filling is ascertained from the ratio of the first area F1 to the second area F2. Finally, the gas filling rn_L in the combustion is ascertained from the measure A.

The actual torque M_ist produced by the engine is corrected in dependence on the ascertained gas filling rrij. However, the measure A can also be used directly for correction of the ascertained actual torque without previously ascertaining the gas filling m-L. It is furthermore feasible to employ any other desired magnitude, which can be derived from the measure A, for correction of the ascertained actual torque.

The gas filling m_L is determined from the product of the measure A and a proportionality factor k_p. The gas filling thus results from the equation:

m-L = A k-p- 11 The proportionality factor k_p is ascertained before the actual determination of the actual torque M-ist. For this purpose, an actual value of the gas filling m_L - ist is measured otherwise than in the combustion chamber of the engine, for example on an engine test bed. The proportionality factor k_p is ascertained from the quotient of the measured actual value m-L-ist of the gas filling and the ascertained measure A for the gas filling with an engine which has the smallest possible tolerances. The proportionality factor thus results from the equation k_p = rp_L-ist / A.

The proportionality factor k_p is performed before ascertaining the actual torque M - ist and is stored in suitable manner. During the ascertaining of the gas filling rn_L, use can then be made of the stored proportionality factor k_p. Ascertaining of the proportionality factor k_p must take place for each type of engine. The ascertained factor can then be used for all engines of that type.

The method is preferably used for lean-burn engines or stratified charge engines for ascertaining the actual torque produced by the engine.

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Claims

1 A method of determining torque produced by an internal combustion engine, comprising the steps of determining an actual characteristic curve for the course of the rotational speed of a component of the engine, determining the gas filling of a combustion chamber of a cylinder of the engine, determining the value of the torque produced by the engine by evaluation of the curve and correcting the determined torque value in dependence on the determined filling, wherein the step of determining the filling comprises establishing a reference line formed by a standard characteristic curve for the component rotational speed or by a base line connecting the minima of the actual curve, determining two areas between the reference line and the actual curve respectively in the two halves of a working stroke of the cylinder, determining a measure for the filling in dependence on at least one of the areas and determining the filling from the measure.

2. A method of determining torque produced by an internal combustion engine, comprising the steps of deterTnining an actual characteristic curve for the course of the rotational speed of a component of the engine, determining the gas filling of a combustion chamber of a cylinder of the engine, determining the value of the torque produced by the engine by evaluation of the curve and correcting the determined torque value in dependence on the determined filling, wherein the step of determining the filling comprises establishing a standard characteristic curve for the component rotational speed with engine operation at lambda equal to one, adjusting the standard curve for a working stroke of the cylinder so that the extremes of the actual and standard curves have the same speed values, determining a first area between the curves in the first half of the stroke, determining a second area between the curves in the second half of the stroke, determining a measure for the filling in dependence on the two areas or given parts thereof and determining the filling from the measure.

3. A method as claimed in claim 1, wherein the step of determining the measure comprises determining the sum, difference or ratio of the areas or the parts thereof.

4. A method of determining torque produced by an internal combustion engine, comprising the steps of determining an actual characteristic curve for the course of the rotational speed of a component of the engine, determining the gas filling of a combustion chamber of a cylinder of the engine, determining the value of the torque produced by the 13 engine by evaluation of the curve and correcting the determined torque value in dependence on the determined filling, wherein the step of determining the filling comprises establishing a base line connecting the minima of the actual curve, determining a first area between the base line and the curve in a first half of a working stroke of the cylinder, determining a second area between the base line and the curve in a second half of that stroke, determining a measure for the filling from one of the areas or the difference between or ratio of the two areas and determining the filling from the measure.

5. A method as claimed in any one of the preceding claims, comprising the step of correcting the actual curve by reference to at lease one magnitude influencing the component speed.

6. A method as claimed in claim 5, wherein the at least one magnitude is indicative of engine oscillating mass.

7. A method as claimed in any one of the preceding claims, wherein the first area is the entire area between the actual curve and the standard curve or base line in the first half of the stroke.

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8. A method as claimed in any one of claims 1 to 6, wherein the first area is the area between the actual curve and the standard curve or base line in the first half of the stroke over a given interval of the course.

9. A method as claimed in any one of the preceding claims, wherein the second area is the entire area between the actual curve and the standard curve or base line in the second half of the stroke.

10. A method as claimed in any one of claims 1 to 8, wherein the second area is the area between the actual curve and the standard curve or base line in the second half of the stroke over a given interval of the course.

11. A method as claimed in any one of the preceding claims wherein the filling is determined from the product of the measure and a proportionality factor.

14

12. A method as claimed in claim 11, comprising the preliminary step of determining the proportionality factor from the quotient of a measured actual value of the gas filling of a combustion chamber of a reference engine with minimum tolerances and a correspondingly ascertained measure for that filling.

13. A method as claimed in any one of claims 1 to 10, wherein the filling is determined from the product of the measure and a characteristic value dependent on at least one predetermined parameter of the engine.

14. A method as claimed in claim 12 or claim 13, wherein the proportionality factor or the characteristic value is determined empirically on an engine test bed.

15. A method as claimed in any one of the preceding claims, wherein the engine is a lean-burn or stratified charge engine.

16. A method as claimed in claim 1 and substantially as hereinbefore described with reference to Fig. 1 or Fig. 2 of the accompanying drawings.