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Title:
IN-CYLINDER PRESSURE DETERMINATION FOR AN INTERNAL COMBUSTION ENGINE
Document Type and Number:
WIPO Patent Application WO/2019/117798
Kind Code:
A1
Abstract:
Methods and devices that estimates the in-cylinder pressure near the top dead centre of the cylinder based on the heat release during burning of fuel in the cylinder are provided. A first in-cylinder pressure curve in a first crank angle range before the start of combustion is determined. A second in-cylinder pressure curve in a second crank angle range after burning fuel of the cylinder is also determined. Then a third in-cylinder pressure curve in a third crank angle range joining the first crank angle range and the second crank angle range. A full in-cylinder pressure curve is formed by the first in-cylinder pressure curve, the second in-cylinder pressure curve and third in-cylinder pressure curve by fitting the first in-cylinder pressure curve and the second in-cylinder pressure curve by a determination of the heat release in the cylinder. Hereby a full in-cylinder pressure curve can be estimated by using an out of cylinder sensor for determining the pressure curve in ranges before and after combustion of fuel in the cylinder.

Inventors:
STENLÅÅS, Ola (Folkparksvägen 166, lgh 1305, Hägersten, 126 77, SE)
RINGSTRÖM, Christopher (Pilgatan 21, Stockholm, 112 23, SE)
Application Number:
SE2018/051302
Publication Date:
June 20, 2019
Filing Date:
December 12, 2018
Export Citation:
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Assignee:
SCANIA CV AB (151 87 Södertälje, 151 87, SE)
International Classes:
F02D35/02; G01M15/08
Domestic Patent References:
WO2017094349A12017-06-08
Foreign References:
FR2991450A12013-12-06
SE539584C22017-10-17
GB2314882A1998-01-14
DE102013214252A12015-01-22
Other References:
ERIKSSON, L. ET AL.: "An Analytic Model for Cylinder Pressure in a Four Stroke SI Engine", SAE TECHNICAL PAPER 2002-01-0371, 2002
GHOJEL, J.I.: "Review of the development and applications of the Wiebe function: A tribute to the contribution of Ivan Wiebe to engine research", INTERNATIONAL JOURNAL OF ENGINE RESEARCH, vol. 11, no. 4, 2010, pages 297 - 312
Attorney, Agent or Firm:
GARDEMARK, Niklas (Scania CV AB, Södertälje, 151 87, SE)
Download PDF:
Claims:
Claims

1 . A method of determ ining the in-cylinder pressure of an internal combustion engine comprising the steps of:

Determ ining a first in-cylinder pressure curve in a first crank angle range before the start of combustion in the cylinder,

Determ ining a second in-cylinder pressure curve in a second crank angle range after combustion in the cylinder, and

Determ ining a third in-cylinder pressure curve in a third crank angle range joining the first crank angle range and the second crank angle range,

Wherein a full in-cylinder pressure curve is formed by the first in-cylinder pressure curve, the second in-cylinder pressure curve and the third in- cylinder pressure curve, and

Wherein the third in-cylinder pressure curve is fitted with the first in- cylinder pressure curve and the second in-cylinder pressure curve based on a determ ination of a heat release in the cylinder,

Wherein the first in-cylinder pressure curve is determ ined using at least one sensor outside the cylinder.

2. The method according to claim 1 , wherein the third in-cylinder pressure curve is fitted using at least one Wiebe function.

3. The method according to claim 2, wherein the third in-cylinder pressure curve is fitted using a double Wiebe function.

4. The method according to any one of claims 1 - 3, wherein the first in- cylinder pressure curve is determ ined by extrapolating the first in-cylinder pressure curve into a crank angle range closer to the top dead center of the cylinder.

5. The method according to any one of claims 1 - 4, wherein the second in-cylinder pressure curve is determ ined using at least one sensor outside the cylinder.

6. The method according to claim 5, wherein the second in-cylinder pressure curve is determ ined by extrapolating the second in-cylinder pressure curve into a crank angle range closer to the top dead center of the cylinder.

7. The method according to any one of claims 1 - 6, wherein a determ ined total heat release in the cylinder is used as a basis to determ ine the shape of the third in-cylinder pressure curve.

8. The method according to claim 7, wherein the total heat release is lim ited by a maxim um heat release determ ined by the difference between an extrapolated first in-cylinder pressure cure and an extrapolated second in-cylinder pressure curve.

9. The method according to claim 7 or 8, wherein the total heat release is lim ited by a maxim um heat release determ ined by the difference between an isobar heat release and an isochoric heat release.

1 0. The method according claim 2 or 3, wherein a parameter of the Wiebe function(s) is set based on the late com bustion pressure.

1 1 . The method according to claim 2 or 3 wherein a parameter of the Wiebe function(s) is set based on sensor values from an in-cylinder pressure sensor.

12. The method according to claim 1 1 , wherein fuel dependent constants in the Wiebe function(s) are set based on values from the in-cylinder pressure sensor. 13. A controller configured to determ ine the in-cylinder pressure of an internal combustion engine in accordance with any one of claims 1 - 12.

14. A motor vehicle comprising the controller according to claim 13.

Description:
IN-CYLINDER PRESSURE DETERMINATION FOR AN INTERNAL

COMBUSTION ENGINE

FIELD OF THE INVENTION

The present invention relates to a method and a device for

determination of in-cylinder pressure of an internal combustion engine.

BACKGROUND

There is a constant aspiration to achieve control of an internal combustion engine in such a manner that fuel used therein is burned in the engine’s cylinders, while generating a maximum amount of energy/fuel work output from the engine and a m inim um amount of em issions of environmentally hazardous pollutants. It is of im portance in such aspiration to have constant knowledge of the internal com bustion engine’s operating conditions. One im portant source of information is the pressure in the cylinder(s) of the internal com bustion engine. This information can be obtained with pressure sensors mounted inside the cylinders. A drawback with pressure sensors is that they are expensive and have issues with aging.

To address this, it has been suggested to determ ine the in-cylinder pressure without the use of pressure sensors. See e. g. Gustafsson, M . 201 5. "Crank Angle Based Virtual Cylinder Pressure Sensor in Heavy-Duty Engine Appl ication. " Master, Institutionen for systemteknik,

Fordonssystem , Linkopings universitet. Also, FR2991 450 relates to estimation of the pressure inside a com bustion cham ber of an internal combustion engine. SUMMARY OF TH E I NVENTION

It is an object of the present invention to provide methods and devices, which at least partly solve the above problems, and which are im proved in at least some respect in relation to prior art methods and devices.

This object is achieved with the method and the devices as set out in the accompanying claims.

As has been realized, determ ining a full in-cylinder pressure curve is difficult without using an in-cyl inder sensor. This is due to the problem that around the top dead centre out-of cylinder sensors will not provide a satisfactory estimate of the in-cylinder pressure. To solve this problem a method that estimates the in-cyl inder pressure near the top dead centre of the cylinder based on the heat release during burning of fuel in the cylinder has been developed.

In accordance with one em bodiment a method of determ ining the in- cylinder pressure of an internal com bustion engine is provided. In

accordance with the method a first in-cylinder pressure curve in a first crank angle range before the start of combustion in the cylinder is determ ined. A second in-cylinder pressure curve in a second crank angle range, typically after com bustion, in the cylinder is also determ ined. The first and second in-cylinder pressure curves are based on a signal representing the engine speed. Then a third in-cylinder pressure curve in a third crank angle range joining the first range and the second range is formed. The third in-cylinder pressure curve is thus, formed in a crank angle range around the top dead center of the cylinder. A ful l in-cylinder pressure curve is formed by the first in-cylinder pressure curve, the second in-cylinder pressure curve and third in-cylinder pressure curve by fitting the first in-cylinder pressure curve and the second in-cylinder pressure curve by a determ ination based on a heat release in the cyl inder. Hereby, a full in-cylinder pressure curve can be estimated by using an out of cylinder sensor for determ ining the pressure curve in ranges before and after com bustion of fuel in the cylinder. The zone around the top dead center where it has been found difficult to estimate the in-cylinder pressure using, for example, out of cylinder sensors, such as engine speed sensors, is estimated using a curve that is fitted with the pre-burning of fuel curve and the post burning of fuel curve such that the curve in the zone around the top dead center matches an estimated heat release estimated during the burning of fuel in the cylinder. Hereby a good and robust estimation of the full in-cylinder pressure can be obtained that includes the zone around the top dead center.

In accordance with one embodiment, the third in-cylinder pressure curve is fitted using at least one Wiebe function. Hereby, a function that can provide a good fitting of the curve in the zone around the top dead center can be obtained.

In accordance with one embodiment, the third in-cylinder pressure curve is fitted using a double Wiebe function.

The parameters of any such Wiebe function can be recalculated for each full combustion cycle. Hereby, the Wiebe function can be made to fit well both with the curve used for pre-burning of fuel and the curve used for post-burning of fuel.

In accordance with some embodiments, the first and or second in-cylinder pressure curve is determ ined using at least one sensor outside the cylinder. Hereby, an already existing sensor such as a crank angle sensor can be used to provide input to an algorithm for determ ining the in-cylinder pressure.

In accordance with some embodiments, the first in-cylinder pressure curve and / or second in-cylinder pressure curve is determined by extrapolating an in-cylinder pressure curve into a range closer to the top dead center of the cylinder. Hereby, a first curve and or a second curve that can be used as a basis for an overall in-cylinder curve can be obtained. In accordance with one em bodiment, a determ ined total heat release in the cylinder is used as a basis to determ ine the shape of the third in-cyl inder pressure curve. Hereby, a first estimate of the heat release can be obtained that can be used to form a basic estimation of the full in-cylinder pressure curve.

In accordance with one em bodiment, the total heat release is lim ited by a maxim um heat release determ ined by the difference between an

extrapolated first in-cylinder pressure cure and an extrapolated second in- cylinder pressure curve. In some em bodiments the total heat release is lim ited by a maxim um heat release determ ined by the difference between an isobar heat release and an isochoric heat release. Hereby lim its on the heat release can be easily obtained. In addition, by com paring two heat release types in terms of a resulting pressure curves and the resulting work output, lim its of start of com bustion can also be determ ined.

In accordance with one em bodiment, the late com bustion pressure is used as a basis to set a parameter of the Wiebe function(s). In particular a pressure determ ined in the range of the second in-cylinder pressure curve can used as a basis to set a parameter of the Wiebe function(s). Hereby, the parameterization of the Wiebe function, in particular a double Wiebe function is facilitated.

In accordance with one em bodiment, sensor values from an in-cylinder pressure sensor is used to set parameters of the Wiebe function(s). By providing an in-cylinder sensor in at least one cylinder of an engine. The sensor output from such a sensor can be used to fine-tune parameters in the Wiebe function. In particular fuel dependent constants in the Wiebe function(s) can be set based on values from the in-cylinder pressure sensor (s). Thus, the engine speed can be used to provide a full cylinder curve. The result can in accordance with some em bodiment be fine-tuned based on another signal representing the in-cylinder pressure for at least one cylinder. The another sensor used can typically be a sensor other than a sensor sensing the engine speed. For exam ple, if one in-cylinder pressure sensor is used in one cyl inder, the measured in-cylinder pressure can be used to fine-tune the model for al l cylinders. In particular the parameters of the Wiebe function can be adjusted in this manner. The fine tuning can be made based on an error signal representing the difference between a current model value and the value measured by the other sensor. Also, the signal also an im proved version can be obtained if at least one cylinder pressure sensor is used.

The invention also extends to a controller for executing the method as set out above. The invention also extends to a motor vehicle provided with such a controller.

BRI E F DESC RI PTION OF TH E DRAWI NGS

Below are descriptions of exam ple em bodiments of the invention, with reference to the enclosed drawings, in which:

- Fig. 1 is a flow chart illustrating steps that can be performed when determ ining an in-cyl inder pressure curve,

- Figs. 2 and 3 are flow charts i llustrating some detai led steps of the flow chart in Fig. 1 ,

- Fig. 4 is a diagram illustrating form ing of a full in-cylinder pressure curve.

- Fig. 5 is a diagram illustrating pressure curves for different types of heat release, as function of cylinder volume, as determ ined by virtual sensor calculations of the in-cylinder pressure near the top dead centre, and

- Fig. 6 is a view of a motor vehicle having a device for calculating the in-cylinder pressure. DETAILED DESCRIPTION

The invention will now be described more fully hereinafter with reference to the accompanying drawings, in which certain embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as lim ited to the embodiments set forth herein; rather, these embodiments are provided by way of example so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. For example, like or sim ilar components or steps of different embodiments can be exchanged between different embodiments. For example, the sensor used to provide input to the pressure determ ination is a crank angle sensor. However other methods for estimating the in-cylinder pressure using sensor outside the cylinder can be used such as the sensor arrangement described in SE539584C2. Some steps or components can be om itted from different embodiments. Like numbers refer to like elements throughout the description.

In Fig. 1 , a flow chart illustrating an exemplary embodiment of a method that can be used to determ ine an in-cylinder pressure. The determ ination is based on the crank angle Q and the first and second derivative of Q. The crank angle can be determ ined by a crank angle sensor. It is to be noted that some of the steps below can be om itted or replaced by sim ilar steps. First in a step 10 a model of the crank shaft is determ ined. For example, the crank shaft can be modelled as a rigid component or some more advanced model could be employed with masses, springs and dampers to more accurately describe the dynam ical behaviour of the system . The crankshaft model can then calculate the pressure curve with good accuracy during the compression stroke and most of the expansion, including a portion of the late combustion based on the crank angle curve and its first and second derivative. The cylinder volume is then input in a step 20. The cylinder volume is determ ined by geometric relations and the crank angle. This cylinder volume can be adjusted to account for deviations from the geometric relations. This adjustment can in one embodiment be set constant. In other, more advanced settings, the cylinder volume adjustment can be set to be dependent on e.g. cylinder pressure and/or engine temperature. Next, in a step 30, two isentropic pressure curves are determ ined. The two isentropic pressure curves correspond to the cylinder compression curve and the cylinder expansion curve. In step 30, pressure curves for the portions of the in-cylinder pressure are determ ined for the crank angles when fuel is not burned in the cylinder. In other words, a first portion for pre-burning of fuel is determ ined and a second portion for post-burning of fuel in the cylinder are formed where the different portions are taken from the pressure curve for pre-burning of fuel and pressure curve for post-burning of fuel respectively. The first and second portions can be based on an out-of cylinder sensor such as a crank angle sensor. Also, the first and second portions can be extrapolated into a range of the crank angle where fuel is burned to form a basis for an estimation of the in-cylinder pressure around the top dead centre where the in-cylinder pressure is difficult to determ ine only using an out-of cylinder sensor. The isentropic pressure curves can either be extrapolated from pressure curves from the crankshaft model or alternatively be calculated from the boost pressure at inlet valve closing for the pre-combustion pressure curve and reverse from the exhaust pressure at outlet valve opening for the post-combustion pressure curve if boost and exhaust pressure sensors are mounted. The curves are calculated from the isentropic relation using the change in volume for each step in crank angle and from estimating the specific heat ratio based on temperature and the composition of air and exhausts in the cylinder mass.

Then in a step 40, work and load for the cylinder is determ ined. In Fig. 2, a more detailed example of how this can be performed is shown. Next, in a step 50 lim its for the in-cylinder pressure curve in an interval around the crank angle degree of zero are set based on values determ ined based on a time for start of combustion (SOC) and an isochoric and isobaric heat release (HR). The start of combustion that results in a pressure curve resulting in the same work as estimated previously can then be determ ined for the two types of heat releases. This gives the lim its of start of com bustion. In a step 60 a combined in-cyl inder pressure curve is formed. This can be performed as described in the exem plary embodiment described in conjunction with Fig. 3. Thus, in step 60, a full , in-cylinder pressure curve is formed by a first in-cylinder pressure curve in a range before the top dead center of the cylinder based on the cyl inder

com pression curve, a second in-cylinder pressure curve in a range after the top dead center of the cylinder based on the expansion curve, and a third in-cylinder pressure curve in a range including the top dead center of the cylinder. A full in-cylinder pressure curve is formed by the first in- cylinder pressure curve, the second in-cylinder pressure curve and third in-cylinder pressure curve, and the third in-cylinder pressure curve is fitted with the first in-cyl inder pressure curve and the second in-cylinder pressure curve by a determ ination of the calculated heat release in the cylinder. In step 60, the first formed full in-cylinder pressure curve is a rough estimation to be able to estimate the wall heat losses and the cum ulative heat release.

The third portion of the curve can be formed by assum ing or calculating a normal distributed heat release rate. Iteratively the cum ulative heat release can be calculated such that the resulting work from the resulting pressure trace corresponds to the previously estimated work, i. e. the work output form step 40.

The full in-cylinder curve determ ined in step 60 can be im proved. For example, in a step 70 a volume correction can be applied. Thus, due to the high pressures within the cyl inder, deformations can be present in the cylinder. Thus, only using the geometric form of the cylinder can give an erroneous result. The volume estimation can however be corrected by some known model based on the estimated pressure within the cylinder and tem perature of the engine. The pressure used can be the pressure determ ined in step 60. The tem peratures for different com ponents can be assumed to be approximate tem peratures for regular warm engine operations. The start of com bustion (SOC) and duration of pre-m ixed com bustion can be estimated from the derivative of the kinetic power in a step 80. Before the start of com bustion, the shape of the derivative of the kinetic power follows the shape of the derivative of the motored piston power. In other words, the power suppl ied to the pistons when dragging the engine is the power from the in-cylinder pressure. When the engine is dragged it is possible the estimate the full in-cyl inder pressure cycle because there is no burning. Also, in accordance with some em bodiments the process can be assumed to be isentropic. By assum ing a constant load, and determ ine the kinetic power, the derivatives of the two-pressure curves can be com pared for the case with a dragged motor and when com bustion takes place. The SOC can be determ ined from a com parison of curves

representing these two scenarios. Just before the top dead centre (TDC), both derivatives increase as the lever length is significantly reduced resulting in an increasing piston power. After TDC this increase in the motored piston power starts decreasing. The kinetic power, however, keeps on increasing sim ilarly to the actual piston power as an effect of the combustion adding energy. Thus, the SOC can for example be determ ined by finding the location where the difference between the second derivative of the kinetic power and the second derivative of motored piston power becomes below 0. 1 35 meaning that the motored piston power increase has decreased more than the indicated power derivative and com bustion must have started.

Next, in a step 90, the late com bustion pressure derivative can be determ ined by calculating the pressure derivative of the pressure curve for the expansion stroke from the crankshaft model. Then in a step 1 00 a single or preferably double Wiebe function can be used to fit the heat release during the com bustion. As the com bustion in a diesel engine can be divided into different phases a single Wiebe function may not be accurate enough to describe the full com bustion. Thus, two functions, one for the prem ixed com bustion and one for the diffusive com bustion of the engine can be used. The parameters in the Wiebe function(s) used can advantageously be set such that the Wiebe function(s) gives a pressure curve that correspond to the estimated work and that the late combustion pressure derivative correspond to the pressure derivative of the pressure curve resulting from the crank shaft model used. Estimation of the prem ixed start of combustion and duration can be used to achieve an improved accuracy in the fitting of the Wiebe functions.

When the Wiebe functions have been parametrised, the burn rate has been determ ined. The heat release is then calculated from the burn rate and the total cumulative heat release. Then, by using the first law of

thermodynamics for a closed system, the change in pressure from a step in crank angle can be determined from the calculated volume, its

derivative, current pressure, wall heat loss rate and heat release rate. The specific heat ratio can be determ ined from an estimation of the

temperature with for example the ideal gas law and the mass fraction burnt fuel. The pressure trace can then be determ ined for the full combustion numerically with for example in a step 1 10.

The pressure derivative can be estimated with the well-known expression from the first law of thermodynam ics.

Where Q is the heat, g is the specific heat ratio and V is the volume.

Finally, in a step 120 the final in-cylinder pressure curve is output.

In Fig. 2, details of some exemplary steps that can be carried out in step 40 in Fig. 1 are described. Thus, first in a step 40.10, the kinetic energy and power of the moving parts of the engine are determ ined based on the mass and inertia of the engine parts in motion and the angular velocity and acceleration of the crankshaft. Next, in a step 40.20, piston work and power are determ ined from using the isentropic pressure curves pre- combustion and post-combustion for each cylinder. Then, in a step 40.30, the values can be corrected for exhaust pressure. Based on the exhaust pressure correction the post-combustion isentropic pressure curve can be determ ined and fine-tuned in a step 40.40. Then, in a step 40.50, the crank angle with zero piston power is determ ined where no combustion is assumed to be present in any cylinder. Further, in a step 40.60, power to load and other auxiliary components are determ ined from the value of the kinetic power of the engine parts in motion. Finally, the net work, power and torque can be determ ined in a step 40.70 based on the separate determ inations in the previous steps. Flereby the work and load for the cylinder can be determined.

In Fig. 3, details of some steps that can be carried out in step 60 in Fig. 1 are described. This first in a step 60.10 the start of combustion (SOC) and the duration of the combustion are determ ined. Next in a step 60.20 it is assumed that the burning during combustion is according to a normal distribution. Then, in a step 60.30, the heat release rate is determ ined based on this assumption. Then in a step 60.40 the curve (trace) for the pressure according to the cylinder pressure extracted from the heat release equation is obtained. Then, in a step 60.50 an iterative procedure for obtaining the gross indicated work is initiated. The procedure in step 60.50 executed by returning to step 60.30 via steps 60.60 and 60.70 until the gross work can be determined in a step 60.80. In step 60.60 the indicated work error is determ ined. Further, in step 60.70, the cumulative heat release is determ ined and used as an input value to step 60.30 in the iterative procedure. Flereby, a full in-cylinder pressure curve can be obtained.

Thus, a full in-cylinder pressure curve can be provided that is formed by a first, pre-combustion, portion determ ined based on some out-of cylinder sensor such as a crank angle sensor and a second, post-combustion portion based on some out of cylinder sensor such as a crank angle sensor. The two portions are joined by a third portion estimating the in- cylinder pressure during a range where the in-cylinder pressure is difficult to determ ine using e. g. a crank angle sensor. The third portion in

particular com prises the top dead centre (TDC) of the in-cyl inder pressure curve. In other words, an out-of cylinder sensor senses the pressure curve by acceleration and decelerations in the engine speed. The engine speed will provide a good estimate of the in-cylinder pressure, but for a range around the top dead centre. However, knowing the engine speed, it is possible to, using a model of the vehicle as described herein, determ ine the resulting full pressure curve.

In Fig. 4 such a com bined, ful l, in-cylinder pressure curve is illustrated.

Fig. 4 i llustrates a full in cylinder pressure curve denoted“virtual sensor pressure trace”. The figure shows the in-cylinder pressure as a function of the crank angle. The crank angle has been divided into three ranges here termed zones. In zone 1 , i. e. in a crank angle range before start of combustion and before the TDC, the in-cylinder pressure can be

determ ined based on an out of cylinder sensor with good accuracy.

Likewise, in zone 3, in a crank angle range post com bustion an out of cylinder sensor with good accuracy. In a zone 2 there-in-between the in- cylinder can be estimated as described herein to provide a ful l in-cylinder pressure curve. The full in cylinder pressure curve is thus in the exam ple of Fig. 4 formed by the first portion denoted“motored pressure trace”. The first portion can e. g. be determ ined based on the output from a crank angle sensor in a range before start of com bustion for the cylinder to determ ine the in-cylinder pressure in this range. The first portion can be extrapolated for the entire crank angle range as is shown in Fig. 4. The full in cylinder pressure curve is also formed by the second portion denoted “ful ly burned pressure trace”. The second portion can e. g. be determ ined based on the output from a crank angle sensor in a range after com bustion for the cylinder has ended to determ ine the in-cyl inder pressure in this range. The second portion can be extrapolated for the entire crank angle range as is shown in Fig. 4. The first and second portions are joined by a third portion to form the full in-cylinder pressure curve. The third portion is determ ined based on the heat release modelled during the com bustion. As can be seen in Fig. 4 the third portion is lim ited by the curves for isochoric heat release during com bustion and isobaric heat release during

combustion. The third portion is also lim ited by the values for the

extrapolated first portion and second portion.

In Fig. 5, an exem plary heat release graph is shown together with a graph for isochoric heat release and a graph for isobaric heat release. Once the heat release for the cyl inder has been determ ined the third portion can be calculated to join the first and second portions as described above. The curve of the third portion is preferably fitted using some function such as a Wiebe or double Wiebe function described above to provide an in-cylinder pressure curve that is smooth. To im prove the parametrization of the Wiebe curve input from an in-cylinder sensor can be used. Such an in- cylinder sensor can then be placed in only one cylinder of the engine and provide sensor values that relates to parameters that are not cyl inder specific such as e. g. fuel quality. Because, the parameters of the Wiebe function can be set for each com bustion cycle, it is made possible to optim ize the Wiebe parameters for the conditions currently present. The Wiebe function parameters can then be periodically updated. In particular the Wiebe parameters can be up-dated on a cycle by cycle basis. Flereby a better fit of Wiebe parameters can be obtained.

In Fig. 6, a truck 1 00 com prising an internal com bustion engine 1 1 0 and a controller 1 1 2 is depicted. The methods and devices as described above can be implemented in the truck using suitable software executed by the controller based on sensor input for at least one sensor provided on the engine 1 1 0.

The controller 1 1 2 can be any kind of electrical device or electronic circuitry and can advantageously be configured to execute com puter program code for the im plementation of a method according to the above. The software can for exam ple be included in a com puter program , loadable into the internal memory of a com puter, such as the internal memory of an electronic control device of an internal com bustion engine. Such a com puter program is suitably provided via a computer program product, comprising a non- transitory data storage medium readable by an electronic control device, which data storage medium has the computer program stored thereon. Said data storage medium is e. g. an optical data storage medium in the form of a CD-ROM, a DVD, etc. , a magnetic data storage medium in the form of a hard disk drive, a diskette, a cassette, etc. , or a Flash memory or a ROM, PROM, EPROM or EEPROM type memory.