Method for estimating cylinder pressure

Abstract

The invention relates to a method (100) for estimating a cylinder pressure (CP) in an internal combustion engine arrangement (10), the method comprising the steps of: initiating (110) an opening of a valve by an actuator during an expansion stroke; monitoring (120) the valve to determine a point in time (Tp) when the valve opens; determining (130) a differential pressure (DP) between the combustion cylinder and a position in a fluid medium exhaust passage (29, 39, 60) downstream said valve at the point in time (Tp); receiving (140) data being indicative of a pressure (EP) in the fluid medium passage at the point in time (Tp); and determining (150) the cylinder pressure (CP) at the point in time (Tp) based on the determined differential pressure (DP) and the data indicative of the pressure in said fluid medium passage.

Claims

1. A method for estimating a cylinder pressure (CP) in an internal combustion engine arrangement, said internal combustion engine arrangement comprising an internal combustion engine having a combustion cylinder and a reciprocating piston movable within said combustion cylinder between a bottom dead center (BDC) and a top dead center (TDC), and further a flow control valve assembly adapted to regulate the flow of a fluid medium passing through the flow control valve in fluid communication with the combustion cylinder and comprising a valve operable between an open position and a closed position and an actuator operable to provide an opening force for opening the valve, characterized by the method comprising the steps of: initiating an opening of said valve by said actuator during an expansion stroke; monitoring said valve to determine a point in time (Tp) when said valve opens; determining a differential pressure (DP) between a gas pressure level of the fluid medium in said combustion cylinder and a pressure level of the combustion gas in a fluid medium passage downstream said valve at said point in time (Tp); receiving data being indicative of a pressure (EP) in said fluid medium passage at said point in time (Tp); and determining the cylinder pressure (CP) at said point in time (Tp) based on the determined differential pressure (DP) and said data indicative of the pressure in said fluid medium passage.

2. The method according to claim 1, further comprising the step of estimating cylinder pressure as a function of crank angle degrees (CAD) of the reciprocating piston, as defined from the top dead center, based on the determined cylinder pressure (CP) at said point in time by modeling.

3. The method according to claim 2, wherein said modeling in said step is any one of a theoretical internal combustion model and an empirical internal combustion model.

4. The method according to claim 2, wherein said method comprises the step of determining a peak cylinder pressure (PCP) from said estimated cylinder pressure as a function of the crank angle degrees.

5. The method according to claim 2, further comprising the step of regulating the flow of fluid medium to an inlet valve based on said estimated cylinder pressure as a function of the crank angle degrees.

6. The method according to claim 1, wherein said step of monitoring said valve to determine a point in time (Tp) when said valve opens further comprises the step of sensing a position of the valve.

7. The method according to claim 6, wherein the flow control valve assembly comprises a positioning sensor, and said step of monitoring said valve to determine a point in time when said valve opens is performed by sensing the position of the valve by means of said positioning sensor.

8. The method according to claim 1, wherein said position in the fluid medium passage corresponds to a position in one of a fluid medium port or a fluid medium manifold.

9. The method according to claim 1, further comprising the step of determining a temperature in said fluid medium passage by a temperature sensor.

10. The method according to claim 1, wherein the step of initiating an opening of the valve during the expansion stroke further comprises the step of activating the actuator to generate the opening force on the valve.

11. The method according to claim 1, wherein the step of initiating an opening of the valve during the expansion stroke is performed prior to the actuator being capable of delivering the opening force for opening the valve.

12. The method according to claim 1, wherein the step of initiating an opening of the valve during the expansion stroke is performed at a given crank angle degree of the reciprocating piston from the top dead center during the expansion stroke.

13. The method according to claim 1, further comprising the step of determining a combustion start point by monitoring engine vibrations by a vibration sensor.

14. The method according to claim 1, wherein said flow control valve assembly is an exhaust flow control valve assembly and said fluid medium passage is an exhaust passage.

15. The method according to claim 1, wherein said flow control valve assembly is an inlet flow control valve assembly and said fluid medium passage is an inlet passage.

16. An internal combustion engine arrangement comprising a control unit for controlling said internal combustion engine arrangement, characterized in that the control unit is configured to perform any one of the steps of the method according to claim 1.

17. A vehicle comprising an internal combustion engine arrangement according to claim 16.

18. A computer program comprising program code means for performing the steps of claim 1 when said program is run on a computer.

19. A computer readable medium carrying a computer program comprising program means for performing the steps of claim 1 when said program means is run on a computer.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non-limiting detailed description of exemplary embodiments of the present invention, wherein:

(2) FIG. 1a is a side view of a vehicle in the form of a truck comprising an internal combustion engine arrangement adapted to be operated according to a method of an example embodiment of the present invention;

(3) FIG. 1b is a schematic drawing of an internal combustion engine arrangement in the vehicle in FIG. 1, in which there is provided a cylinder comprising a combustion chamber and a reciprocating piston; FIG. 1b also schematically illustrates an example embodiment of an operational step of the method according to the present invention, in which one of the valves is in an open state during an expansion stroke of the combustion cycle of the engine;

(4) FIG. 2 schematically illustrates parts of an example of a flow control valve, which is intended for controlling a flow of a fluid medium in an internal combustion engine arrangement;

(5) FIG. 3a is a block diagram depicting steps in a method according to an example embodiment of the present invention;

(6) FIG. 3b is a block diagram depicting steps in a method according to another example embodiment of the present invention.

(7) With reference to the appended drawings, below follows a more detailed description of embodiments of the invention cited as examples.

DETAILED DESCRIPTION OF EXAMPLE EMBODIMENTS OF THE INVENTION

(8) The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments of the invention are shown. The invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided for thoroughness and completeness. Like reference character refer to like elements throughout the description.

(9) FIG. 1a is a side view of a vehicle in the form of a truck, such as a heavy-duty truck, in particular a tractor for a semitrailer. The vehicle 1 in FIG. 1a comprises an internal combustion engine arrangement 10 adapted to be operated according to a method of an example embodiment of the present invention. The internal combustion engine 30 arrangement 10 comprises an internal combustion engine 12, as described below in more detail. The internal combustion engine 12 is generally operated in a four stroke fashion. In this example embodiment, the internal combustion engine is an internal diesel combustion engine, i.e. an engine designed to work according to the diesel process.

(10) In addition, the internal combustion engine arrangement 10 comprises a control 35 unit 600 to perform the operational steps of the method according to the example embodiments as described herein, and which are further described in relation to FIGS. 3a and 3b.

(11) Turning now to the parts of the engine 12, FIG. 1b depicts one cylinder of the engine in the vehicle in FIG. 1a. As illustrated in FIG. 1b, the engine 12 generally comprises a cylinder 3 and a reciprocating piston member 23, which is often simply denoted as the piston 23. Typically, the internal combustion engine includes a plurality of cylinders, e.g. six to eight cylinders 3, each one having a corresponding piston 23.

(12) The piston 23 is arranged to reciprocate between its uppermost position TDC, and its lowermost position BDC. In FIG. 1b, the piston 23 is located close to its BDC, while the piston position in FIG. 1b indicated by dashed lines illustrates the TDC position. The volume within the cylinder 3 between the BDC of the piston 23 and the cylinder top is generally referred to as a combustion chamber 4.

(13) Each cylinder 3 of FIG. 1b comprises at its vertical top end at least one and typically a multiple number of inlet channels 21 for inlet air, and at least one and typically a multiple number of exhaust channels 22 for exhaust gases from the fuel combustion process taking place within the cylinder 3. The exhaust channel(s) typically interconnect(s) with an exhaust passage of an exhaust aftertreatment system. The engine also typically comprises a fuel injector for injecting fuel into a combustion chamber of the engine cylinder. Optional, although not shown, the fuel injector can comprise a vibration sensor configured to detect vibrations generated from combustion process. The vibration sensor can also be configured to detect when the fuel injector is activated and to transfer relevant information to the control unit for further processing.

(14) Referring again to FIG. 1b, each inlet channel 21 has an inlet valve 20 for controlled inlet of incoming fluid medium, and each exhaust channel 22 has an exhaust valve 30 for controlled outlet of exhaust gases. In particular, the exhaust valve 30 is arranged to control fluid communication between the respective cylinder 3 and an exhaust port 39 of the exhaust channel 22 or the exhaust passage 60. Typically, the engine 12 comprises a number of exhaust valves 30 in fluid communication with the combustion chamber 4 and configured to regulate the evacuation of exhaust gases from the combustion chamber to the exhaust passage 60. As will be further described herein, at least one of the exhaust valves 30 is an exhaust flow control valve assembly 38 adapted to control the flow of a fluid medium passing through the exhaust flow control valve assembly. In this example embodiment, each one of the exhaust valves is provided in the form of an exhaust flow control valve assembly. The inlet valve 20 is arranged in fluid communication with the combustion chamber 4 and configured to regulate the supply of the incoming fluid medium to the combustion chamber 4. Generally, the engine comprises a number of inlet valves 20 in fluid communication with the combustion chamber 4 and configured to regulate the supply of the incoming fluid medium from an air inlet, which is part of an air inlet passage 29, to the combustion chamber 4. Typically, at least one of the inlet valves 20 is an inlet flow control valve assembly 28 adapted to control the flow of a fluid medium passing through the inlet flow control valve assembly. In this example embodiment, each one of the inlet valves is provided in the form of an inlet flow control valve assembly.

(15) One example of a flow control valve assembly 28, 38 is shown in FIG. 2. This type of flow control valve assembly is one conceivable example embodiment of a flow control valve assembly intended for the system and the method as described herein in relation to the FIGS. 3a and 3b. The flow control valve assembly can be arranged as the inlet valve 20, thus denoted as the inlet flow control valve assembly 28 or as the exhaust valve 30, and thus denoted as the exhaust flow control valve assembly 38. In this example embodiment, and in the description in relation to FIG. 2, both inlet and exhaust flow control valve assemblies are of the same type, and the description is therefore applicable to both of them. The flow control valve assembly 28, 38 can be controlled in various manners. Typically, although not strictly necessary, the valve assembly 38 comprises an actuator 91 operatively connected to a valve 92 and configured to operate the valve by means of a pneumatic pressure. The actuator 91 is typically configured to control the opening and closure of the valve at a given point in time. By way of example, the actuator 91 is typically configured to control the opening and closure of the valve at a given point in time by receiving a signal from the control unit 600 or the like. Hence, in this example embodiment, the flow control valve assembly 28, 38 is a pneumatic flow control valve assembly. If the flow control valve assembly is a pneumatic flow control valve assembly, each one of the flow control valve assemblies 28, 38 is typically in fluid communication with a common air compressor (not shown), or a corresponding separate air compressor, being configured to supply compressed air to the corresponding flow control valve(s).

(16) The valve 92 is here a lift type valve member. By way of example, the lift type member can be a conventional poppet valve or the like, as shown in FIGS. 1b and 2. The actuator 91 of the valve is configured to operate the valve 92 by pneumatic pressure. As such, the valve 92 is a pressure activated valve. In this example, each one of the flow control valve assemblies 28, 38 comprises a pneumatic actuator operatively connected to a corresponding valve.

(17) In particular, as shown in FIG. 2, the actuator 91 of the valve assembly is configured to operate the valve via an actuator piston 95. The actuator 91 is in fluid communication with a pressurized air medium (not shown) via an air inlet 97 and an air outlet 98. In this manner, the pneumatic valve actuation utilizes compressed air to control the valve opening of the valve, i.e. to operate the valve between an open fluid medium state and a closed fluid medium state. Accordingly, the actuator 91 comprises at least the air inlet 97 for the pressure fluid medium and at least the air outlet 98 for the pressure fluid medium. The pressurized air flowing in via the air inlet 97 is directed towards the actuator piston 95 by a means of an air inlet valve 99. The air inlet valve 99 is disposed in the air inlet and configured to open and close the air inlet so as to control the flow of air to the actuator piston 95. Further, there is disposed an air outlet valve 96 in the air outlet 98, which is configured to open and close the air outlet in order to permit air to discharge from the actuator. Typically, as shown in FIG. 2, the actuator piston 95 is disposed in a chamber 84 defining a space for a reciprocating movement of the actuator piston 95. The actuator piston 95 is operable between a first position (an upper position), in which the valve 92 is in the closed state, and a second position (a lower position), in which the valve 92 is in the open state. In FIG. 2, the actuator is in the upper position, i.e. in the closed state. The actuator piston 95 is operable between the first position (upper position) and the second position (lower position) by pressurizing and depressurizing the actuator. In addition, the flow control valve comprises a spring 87 arranged in-between the valve 92 and the actuator piston disc 95 so as to return the valve to its original position, i.e. corresponding to the upper position of the actuator piston disc 95.

(18) The flow control valve assembly 28, 38 may also have a hydraulic circuit 83 comprising a hydraulic circuit chamber. The purpose of the hydraulic circuit is to further control or dampening the movement of the actuator piston disc 95. The hydraulic circuit can be controlled by the hydraulic valve 85.

(19) Moreover, the flow control valve assembly 28, 38 can include a control valve unit 82 to control the operation of the flow control valve assembly upon a signal from the control unit 600. By way of example, the actuator 91 is configured to operate upon the signal received from the control unit 600 to the control valve unit 82. The control valve unit may also include a sensor arrangement or the like to monitor the various components of the flow control valve assembly. Also, the control valve unit 82 is typically configured to control the various components of the flow control valve assembly, as mentioned above.

(20) It should be readily appreciated that although the example embodiment above relates to a system in which each one of the inlet valves and each one of the exhaust valves is a flow control valve assembly, it may be sufficient that only one of the exhaust valves is a flow control valve assembly for performing the method as described in relation to FIG. 2.

(21) Turning now to the operation of the engine, the engine according to one example embodiment is arranged to provide in each cylinder 3 a so called repeated four-stroke cycle. That is, the sequence of the operation of the engine per cylinder is based on the sequences of a conventional four stroke cycle. One example embodiment of the sequences of a method adapted to operate the engine according to the four stroke cycle includes the steps of performing the intake stroke, the compression stroke, the expansion stroke and the exhaust stroke.

(22) FIG. 3a depicts one example embodiment of the sequences of a method according to the present t invention. The example embodiment of the sequences of the method can be performed on the vehicle internal combustion engine arrangement described in relation to FIGS. 1a-1b and 2. Hence, with reference to FIG. 3a, there is provided a method 100 for estimating a cylinder pressure CP in an internal combustion engine arrangement 10 of a vehicle 1, e.g. as described in relation to the FIGS. 1a-1b and 2. The internal combustion arrangement comprises the flow control valve assembly 28, 38 being in fluid communication with the combustion cylinder 3 and comprising the valve 92 operable between an open position and a closed position and the actuator 91 operable to provide an opening force for opening the valve.

(23) As illustrated in FIG. 3a, the method comprises at least the following steps: initiating 110 an opening of the valve by the actuator during an expansion stroke; monitoring 120 the valve to determine a point in time Tp when the valve opens; determining 130 a differential pressure DP between the combustion cylinder and a position in the exhaust passage 60 at the point in time Tp; receiving 140 data being indicative of a pressure EP in the exhaust passage at the point in time Tp; determining 150 the cylinder pressure CP at the point in time Tp based on the determined differential pressure DP and the data indicative of the pressure in the exhaust passage.

(24) The steps of the method according to the above, and also other steps described below, are performed during operation of the vehicle. Moreover, the method is generally performed either in a standstill operation or in a driving operation.

(25) As mentioned above, the engine can be provided in several different configurations including one or more flow control valve assemblies. The flow control valve assemblies are particularly useful in step 110 so as to initiate the opening of the valve during the expansion stroke. In this example, the flow control valve assembly corresponds to the exhaust valve, i.e. the flow control valve assembly is an exhaust flow control valve assembly 38.

(26) By way of example, the step 110 of initiating the opening of the valve during the expansion stroke further comprises the step of activating the actuator 91 to generate the opening force on the valve 92 (part of the exhaust flow control valve assembly 38). That is, in step 110, the method requests or commands the actuator to generate the opening force, which is typically performed by pressurizing the actuator with the compressed air. As such, the opening of the valve is performed by applying a known opening force on the valve, which is provided by the pressurized actuator. The required opening force for opening the valve depends on type of actuator and on various operational parameters such as pressure levels etc. In this example embodiment, the required opening force is predetermined and data indicative of the required opening force is stored in the control unit 600. The desired predetermined opening force is generally obtained from empirical data. Typically, the step of initiating 110 the opening of the valve during the expansion stroke is performed prior to the actuator being capable of opening the valve.

(27) By way of example, the control unit 600 is configured to initiate the opening of the valve during the expansion stroke. For example, the step of initiating the opening of the valve by the actuator is typically performed during at least a first half of the expansion stroke. That is, the opening of the valve is performed early during the expansion stroke. However, it is also possible that the step 110 of initiating the opening of the valve during the expansion stroke is performed at a given crank angle degree of the reciprocating piston, from the top dead center during the expansion stroke.

(28) Generally, the step 110 further comprises the step of delivering the opening force for opening the exhaust valve during a given subsequent number of crank angle degrees of the reciprocating piston, from the top dead center during the expansion stroke.

(29) It should be ready appreciated that the exhaust valve opens at a point in time when counter-acting forces on the exhaust valve are essentially equal in magnitude. That is, the opening force on the exhaust valve is essentially equal in magnitude to the aggregate amount of the force from the combustion cylinder and the force from the exhaust passage. The forces acting on the exhaust valve can be derivable from the theory of equilibrium of forces in the combustion cylinder acting on the exhaust valve.

(30) Similar to step 110, step 120 is also normally performed during the expansion stroke. One example of the position of the valve in step 120 is illustrated in FIG. 1b, in which the position of the valve 92 is illustrated immediately after opening while the piston performs the expansion stroke. The position of the valve 92 is in this example monitored by means of a sensor arranged in connection with the valve 92, e.g. in the exhaust flow control valve assembly 38. The sensor may for example be a positioning sensor configured to detect and determine the position of the valve. Thus, the step 120 of monitoring the valve to determine the point in time Tp when the valve 92 opens further comprises the step of sensing a position of the valve 92. By way of example, the exhaust flow control valve assembly comprises the sensor (not shown). The data or information indicative of the monitored position of the valve 92 can be temporarily stored in the control unit of the exhaust flow control valve assembly 38, which is described above. Moreover, data relating to the position of valve 92 is transferred from the exhaust flow control valve assembly 38 to the control unit 600 for further processing, e.g. in accordance with the subsequent steps 130, 140 and 150.

(31) In the step 120, the opening of the valve 92 by the actuator 91 is performed by controlling the actuator 91 which is operatively connected to the valve 92. As the exhaust valve 92 is arranged in connection with the exhaust passage 60, i.e. the exhaust port 39 in e.g. FIG. 1b, an opening of the exhaust valve 92 generally implies that the passage between the combustion chamber 4 and the exhaust passage 60 opens in response to the operation of the actuator 91.

(32) While the step 110 and the step 120 are performed during the expansion stroke, the steps 130, 140 and 150 can likewise be performed at another point in time. By way of example, the steps 130, 140 and 150 are performed subsequent the steps 110 and 120 and during the ongoing combustion cycles of the engine. Alternatively, the control unit 600 can gather and store the data from the step 120, and subsequently perform the steps 130, 140 and 150 at another point in time, and also at another location.

(33) The exhaust valve 92 is generally maintained in the open position until the steps 110 and 120 of the method are performed. By way of example, the valve 92 is maintained in the open position at least until the exhaust stroke is completed for the given cycle. Typically, although not strictly required, the valve 92 is thus closed at the end of the exhaust stroke. Therefore, the method optionally comprises the step of positioning the valve 92 in the closed position at the exhaust stroke.

(34) Subsequently, in step 130, the differential pressure DP is determined. The differential pressure is the difference between a gas pressure level of the fluid medium provided into the combustion cylinder and a pressure level of the combustion gas in the exhaust passage 60, which corresponds to the exhaust gas being directed away from the combustion cylinder. By way of example, the differential pressure can be determined by determining the force caused by the differential pressure between the combustion cylinder and a position in the exhaust passage 60 at the point in time Tp. When the force is determined, the differential pressure can be determined by disregarding the relatively small area difference between the upper face of the valve 92, i.e. the side of the valve facing the exhaust passage 60 (see FIG. 1b), and the bottom face of the valve 92, i.e. the side of the valve 92 facing the combustion chamber 4 of the cylinder 3 (see FIG. 1b). Alternatively, the differential pressure can be determined by measuring the pressure in the exhaust passage at the given point in time Tp. The pressure in the exhaust passage at the given point in time Tp can be determined as described in relation to step 140, see below.

(35) It should be noted that the position in the exhaust passage 60 may either refer to the exhaust port 39 (see e.g. FIG. 1b) or the exhaust manifold (not shown). In this example, the step of determining the differential pressure is performed by determining the difference in pressure between the pressure in the combustion cylinder and the pressure in the exhaust port 39 (part of the exhaust passage 60), see e.g. FIG. 1b. The pressure at this position in the exhaust passage can be determined by a pressure sensor (not shown).

(36) Turning now to the step 140 of receiving data indicative of the pressure EP in the exhaust passage at the point in time T.sub.p, the position in the exhaust passage may analogously refer to the exhaust port or the exhaust manifold. In this example, the data in the step of receiving data indicative of the pressure EP in the exhaust passage at the point in time T.sub.p refers to data indicative of the pressure EP in the exhaust port 39, which is illustrated in e.g. FIG. 1b. Accordingly, the pressure EP is monitored at an appropriate position in the exhaust port. The pressure at this position in the exhaust port 39 can be determined by a pressure sensor (not shown). In other words, the pressure sensor is configured to measure a pressure in the exhaust port 39 (i.e. in the exhaust passage 60). The data or information indicative of the monitored pressure EP in the exhaust passage can be temporarily stored in an associated control unit, e.g. the control unit 600. As such, the step 140, as mentioned above, generally also comprises the step of determining the pressure EP in the exhaust passage based on the data indicative of the pressure in the exhaust passage. The pressure sensor is typically configured to transfer data indicative of the pressure EP in the exhaust passage to the control unit 600 for further processing, e.g. in accordance with the subsequent step 150.

(37) Accordingly, in step 150, the cylinder pressure CP at the given point in time is determined based on the determined differential pressure DP and the data indicative of the pressure EP in the exhaust passage. As the differential pressure and the pressure in the exhaust passage are known from the steps 130 and 140, respectively, the cylinder pressure can be determined on the basis of a prevailing equilibrium of forces in the combustion cylinder at the given point in time Tp. That is, when there is equilibrium of forces, the counter-acting forces on the exhaust valve are essentially equal in magnitude.

(38) Moreover, as illustrated in FIG. 3a, the method optionally comprises the step 160 of estimating cylinder pressure as a function of crank angle degrees of the reciprocating piston 23, as defined from the top dead center, based on the determined cylinder pressure CP at the point in time. Typically, the step 160 of estimating cylinder pressure as a function of crank angle degrees of the reciprocating piston 23, as defined from the top dead center, based on the determined cylinder pressure CP at the point in time is performed by modeling. The modeling in the step 160 is any one of a theoretical internal combustion model and an empirical internal combustion model. It is sufficient that the step 160 only estimates a part of the cylinder pressure trace in some implementations of the method according to the example embodiments. The type of model is typically selected in view of type of engine, type of vehicle and type of operational conditions.

(39) By way of example, it becomes possible to determine the peak cylinder pressure (PCP) from the estimated cylinder pressure as a function of crank angle degrees. Thus, in another example embodiment of the method, as illustrated in FIG. 3b, the method additionally comprises the step 162 of determining the peak cylinder pressure from the estimated cylinder pressure as a function of the crank angle degrees.

(40) In addition, the method in this example further comprises the step 170 of regulating the flow of fluid medium into the combustion cylinder by regulating the opening of one or a number of inlet valves based on the estimated cylinder pressure as a function of the crank angle degrees. By regulating the flow of fluid medium to one valve per cylinder, the method can be used for balancing the cylinders of the engine in a simple and efficient manner. Further, it may be even possible to regulate the flow of fluid medium to the valve immediately after step 130.

(41) If the method is used on a number of cylinders, as mentioned above, the control unit can gather information from the number of the cylinders and estimate the cylinder pressure as a function of crank angle degrees for each one of the number of cylinders. By measuring on each one of the number of cylinders of the engine, it becomes possible to detect cylinder-to-cylinder deviation. Thereafter, the detected cylinder-to-cylinder deviation can be used as an input data to control the inlet valves to provide essentially equivalence cylinder pressure trace in each one of the cylinders of the engine.

(42) Moreover, in order to further improve the accuracy of the cylinder pressure estimation, the method may take the temperature in the exhaust passage into consideration. Accordingly, as illustrated in FIG. 3b, the method comprises the step 164 of determining a temperature in the exhaust passage by a temperature sensor. Typically, data or information indicative of the monitored temperature in the exhaust passage can be temporarily stored in an associated control unit, e.g. the control unit 600. However, the temperature sensor is typically configured to transfer data indicative of the temperature in the exhaust passage to the control unit 600 for further processing in the step of estimating the cylinder pressure as a function of crank angle degrees.

(43) It is even possible to take vibrations occurring from the combustion into consideration when determining the cylinder pressure as described above. By way of example, the method can further comprise the step of determining a combustion start point by monitoring engine vibrations by the vibration sensor, as mentioned above. The data or information indicative of the detected vibrations can be handled and processed in a similar manner as the data relating to the temperature, as mentioned above.

(44) It is to be understood that the present invention is not limited to the embodiments described above and illustrated in the drawings; rather, the skilled person will recognize that many changes and modifications may be made within the scope of the appended claims. By way of example, although the steps of the example embodiments have been described in relation to an exhaust valve 30, the method may likewise be performed by using one of the inlet valves 20, or a combination of one engine inlet valve 20 and one engine exhaust valve 30.