Technical field

[001] The present invention relates to method of controlling phasing of combustion of fuel in a multi-cylinder internal combustion engine according to the preamble of claim 1.

[002] The present invention relates to apparatus for controlling combustion in a multi-cylinder internal combustion engine.

Background art

[003] The operational requirements of internal combustion piston engines are becoming more and more demanding. For example, exhaust gas emission requirements of internal combustion piston engines become more and more stringent. In order to cope with such requirements there are various techniques available by means of which the gaseous emissions may be controlled when the engine is running. On the other hand, it is not desirable that the overall performance of the engine will suffer resulted from actions aiming to reduce the emissions.

[004] Publication W02019034260A1 discloses a method in which heat release from combustion of fuel in a cylinder of the engine is utilized for controlling the amount of air involved in the combustion process in the cylinder of the engine.

[005] The amount of air in the charge is an important factor in combustion as such but also controlling the combustion phasing is critical for the engine efficiency. Combustion phasing means controlling the crank angle range (or piston position) during which combustion of fuel introduced into the cylinder is taken place. Traditionally the combustion phasing has been handled as a map-based fuel ignition timing controller, being it a compression ignition or ignition by external heat sources. [006] However, optimal combustion phasing control must also consider certain factors which relate directly to the combustion occurrence, such as cylinder pressure, pressure rise rate, gaseous emissions etc. It is also a common problem that all the cylinders of the engine do not behave equally, for example amount of air introduced into the combustion chamber may vary. Also fuel which is combusted in an internal combustion piston engine may have variations in its composition. This effects, for example, on combustion stability and exhaust gas emissions.

[007] Publication EP3341603 B1 discloses a method for controlling combustion timing in at least one cylinder of an internal combustion engine using gaseous fuel firstly by monitoring flywheel and by using ignition maps, and further by using average heat release timing to adjust the map-based control. According to the publication heat release timing relates to a certain point of time or angular position crankshaft when at least 50% of heat of the combusting fuel is released. The method further comprises steps of monitoring pressure in at least one cylinder such that an average heat release timing is deduced from the monitoring of the pressure. Ignition timing is controlled based on the average heat release timing.

[008] Even if the disclosed method may be advantageous as such there is still room for improving an accuracy of control of combustion of each cylinder of a multi-cylinder internal combustion engine.

[009] An object of the invention is to provide a method of and apparatus for controlling phasing of combustion of fuel in a multi-cylinder internal combustion engine in which accuracy of combustion control is considerably improved compared to the prior art solutions.

Disclosure of the Invention

[0010] Objects of the invention can be met substantially as is disclosed in the independent claims and in the other claims describing more details of different embodiments of the invention.

[0011] According to the invention method of controlling phasing of combustion of fuel in a multi-cylinder internal combustion engine comprising a computer control system which is configured to control cylinder-wise phasing of combustion of fuel, the method comprising: monitoring engine speed and engine load, obtaining a set value for controlling the phasing of combustion by using the engine speed and the engine load as input values for a predefined combustion phasing map, which provides the set value for controlling the combustion phasing, common for all the cylinders of the engine, and obtaining a first feedback value separately for each cylinder by determining a heat release timing at which a predetermined proportion of heat of available combusting fuel is released during one power stroke, and obtaining a second feedback value for controlling the phasing of combustion separately for each cylinder by determining a cumulative heat release Q by using measured pressure values from the cylinder, resulted from combustion of fuel over a crank angle range - O ₂ during which combustion of fuel is taken place, in one combustion cycle of the engine, and determining a mean gross heat release rate Q’ resulted from combustion of fuel by providing a linear fitting to the cumulative heat release Q, a slope of which stands for the mean gross heat release rate Q’, and converting the mean gross heat release rate Q’ into a second feedback signal having the second feedback value; and combining the set value and the second feedback value to form a corrected set value for the computer control system of the engine separately for each cylinder, and combining the corrected set value and the first feedback value to form a final set value for the computer control system of the engine separately for each cylinder.

[0012] By practising the method according to the invention in a multi-cylinder piston engine, the overall performance of the engine is improved thanks to the accurate cylinder-wise control of combustion timing. The method according to the invention can solve problems relating to irregularities in fuel quality, air (oxygen) distribution between cylinders of the engine, and other cylinder-wise fluctuations in operation of the engine. [0013] The term heat release timing means the position of the piston, which can be also defined by the respective crank angle, at which a predetermined proportion of heat of available fuel in the combustion chamber of the cylinder has been released after ignition.

[0014] According to an embodiment of the invention the step of obtaining the second feedback value comprises comparing the mean gross heat release rate Q’ to a nominal gross heat release rate Qn’ value at the monitored engine load, and in case the mean gross heat release rate Q’ is smaller than the nominal gross heat release rate Qn’, the second feedback value is increased, and in case the mean gross heat release rate Q’ is greater than the nominal gross heat release rate Qn’ the second feedback value is decreased, from a second feedback value for the nominal gross heat release rate Qn’. The nominal gross heat release rate Qn’ value as function of engine load can be stored in or made available to the computer control system.

[0015] According to an embodiment of the invention the mean gross heat release rate Q’ is provided from combustion of fuel by providing a Least Square Regression Line to the cumulative heat release Q and defining a fitting for a slope of the Least Square Regression Line to the cumulative heat release Q, which stands for the mean gross heat release rate Q’.

[0016] According to an embodiment of the invention the method further comprises providing cylinder specific mean gross heat release rate Q’ values of successive combustion cycles in each one of the cylinders of the engine and calculating an average value of the cylinder specific mean gross heat release rate Q’ values and using the average value as the mean gross heat release rate.

[0017] According to an embodiment of the invention in the method the pressure from each cylinder of the engine is measured substantially constantly or intermittently during combustion of fuel in a cylinder of the engine at determined crank angles within a crank angle range.

[0018] According to an embodiment of the invention the cumulative heat release Q is determined by using an equation

[0019] by using measured pressure values from the cylinder over a crank angle range O ₀ - Si during which combustion of fuel is taken place.

[0020] According to an embodiment of the invention the first feedback value is a crank angle value O _RQ at which a predetermined proportion of heat RQ of available combusting fuel Q _fuei in the closed combustion chamber of the cylinder is released and it is determined by using an equation by using measured pressure values from the cylinder over a crank angle range So - SRQ during which combustion of fuel is taken place.

[0021] According to an embodiment of the invention a crank angle value at which a predetermined proportion of heat of available combusting fuel is released is determined during several power strokes, calculating an average value of the heat release timing, and determining the first feedback value using the average value.

[0022] According to another embodiment of the invention predetermined proportion of heat RQ of available combusting fuel is 15 - 50% of heat of available combusting fuel Q _fue i.

[0023] According to still another embodiment of the invention predetermined proportion of heat RQ of available combusting fuel is 15 - 25% of heat of available combusting fuel Q _fue i.

[0024] A computer readable memory device comprising instructions which, when executed by a computer, cause the computer configured to control a multi-cylinder internal combustion piston engine to carry out a method according to the invention.

[0025] Apparatus for controlling combustion in a multi-cylinder internal combustion engine comprising a computer controller and means for monitor engine speed, engine load, and crank angle position, and pressure in each one of the cylinders of the engine, wherein the computer controller comprising

- a first control unit configured to determine a set value for controlling the phasing of combustion by using the engine speed and the engine load as input values for a predefined combustion phasing map,

- a timing controller to determine a first feedback value for the computer control system separately for each cylinder by determining a heat release timing at which a predetermined proportion of heat of available combusting fuel is released and

- second control unit configured to determine a second feedback value for controlling the phasing of combustion separately for each cylinder by a heat release determination unit configured to determine a cumulative heat release Q by using measured pressure values from the cylinder over a crank angle range during which combustion of fuel is taken place, in one combustion cycle of the engine, and a heat release rate determination unit configured determine a mean gross heat release rate Q’ by providing a linear fitting to the cumulative heat release Q, a slope of which stands for the mean gross heat release rate Q’, and a heat release rate controller configured to convert the mean gross heat release rate Q’ into a feedback signal having the second feedback value and

- a summing unit to determine a corrected set value for the computer control system of the separately for each cylinder based on the set value and the second feedback value, and

- a combustion phasing control unit which is configured to provide a final set value for transmitting to a charge ignition actuator.

[0026] This makes a multi-cylinder piston engine operate in controlled manner and the overall performance of the engine is improved thanks to the accurate cylinder-wise control of combustion timing. The apparatus according to the invention can solve problems relating to irregularities in fuel quality, air (oxygen) distribution between cylinders of the engine, and other cylinder-wise fluctuations in operation of the engine. This provides extremely accurate cylinder wise combustion control of the engine. [0027] The invention provides a double feedback combustion phasing control. The exemplary embodiments of the invention presented in this patent application are not to be interpreted to pose limitations to the applicability of the appended claims. The verb "to comprise" is used in this patent application as an open limitation that does not exclude the existence of also unrecited features. The features recited in dependent claims are mutually freely combinable unless otherwise explicitly stated.

Brief Description of Drawings

[0028] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates an internal combustion multi-cylinder piston engine and an apparatus for controlling combustion in a multi-cylinder internal combustion engine according to an embodiment of the invention,

Figure 2 illustrates an example of the cumulative heat release and mean gross heat release rate according to an embodiment of the invention, and

Figure 3 illustrates a trend graph of the mean gross heat release rate according to an embodiment of the invention.

Detailed Description of Drawings

[0029] Figure 1 depicts schematically a multi-cylinder internal combustion piston engine 10 and a computer control system 100 configured to control combustion process in the engine 10, particularly cylinder-wise phasing of combustion of fuel. The invention is particularly intended for phasing of combustion of fuel in engines having at least four cylinders and the figure 1 the number of cylinder is shown to be four, as an example. In the following the internal combustion multi-cylinder piston engine 10 will be referred to as an engine 10 for sake of simplicity. The engine 10 comprises a number of cylinders 12 which may be arranged in-line configuration as is shown in the figure or e.g. in V-configuration. Each one of the cylinders is provided with fuel admission means 14, which may, depending on the type of engine, be a direct injection means or fuel admission valve arranged to an air intake channel of the cylinder. The fuel admission means 14 comprise a charge ignition actuator 16. The charge ignition actuator is a system for causing the charge in the cylinder to ignite in controllably manner. Without going deep into various possibilities of igniting a fuel, or the charge, in the combustion chamber of the engine, the practical realization of the fuel ignition actuator depends on operation principle of the engine. The charge ignition actuator may be for example, a fuel injection valve (compression ignition, autoignition), a source of external heat (spark, plasma) or a combination thereof. The charge ignition actuator needs to be controllable by the computer control system 100. For example, in an engine using gaseous fuel as its main fuel, the charge can be ignited by injection of pilot fuel which ignites by compression ignition and ignition of the pilot fuel ignites the main fuel.

[0030] Each one of the cylinders 12 of the engine 10 is provided with means for monitoring pressure in each one of the cylinders, such as pressure sensor 18. The pressure sensors 18 are arranged to provide pressure measurement data to the computer control system 100. The engine is also provided with one or more crank angle sensors 20 or other suitable arrangement, to act as means for monitor engine speed and/or provide crank shaft position information for use in the computer control system 100. The engine is also provided with a load detecting means 22. Load is the drive power being generated by the engine to cope with an external restraining power demand being applied to the engine. For the case where the engine is operating at a constant speed, the load is equal and opposite to the external power demand. The load detecting means may comprise a torque detector and utilize the crank angle sensor, which provides also rotational speed of the engine.

[0031] Generally, each one of the measurement devices or sensors is in data transmission connection with the computer control system 100, for example by a data bus or fiber optics or a like. The measurement data from each one of the sensors is made available to the computer control system 100 for individual processing therein. The computer control system 100 comprises a computer controller 102 and an executable computer program or programs configured to control the combustion of fuel in the engine 10 to carry out the method according to the invention.

[0032] The computer controller 102 comprises a first control unit 114 configured to determine a set value for controlling the phasing of combustion. The first control unit 114 is in a data transfer communication with one or more crank angle sensors 20 and the load detecting means 22. The first control unit is using the engine speed 20 and the engine load 22 as its feed, or input values for obtaining a global set point for timing the combustion phasing as an output signal of the first control unit 114. The first control unit 114 comprises a predefined combustion phasing map 114’, stored in its memory or made available in other way to the first control unit. The combusting phasing map provides a global control value feed for all of the cylinders based on, or as a function of the feed values. In other words, the control value and signal which is eventually controlling the charge ignition actuator 16 of a particular cylinder 12 is based on the global control value generated by the first control unit 114 and corrected by cylinder-dedicated control units.

[0033] In order make the control more accurate the computer controller comprises a timing controller 116 which is configured to provide a first feedback value for the computer control system. The timing controller is configured to determine a heat release timing, i.e., crank angle value, at which a predetermined proportion of heat of available combusting fuel is released during the power stroke. The timing controller 116 is in data transfer communication with respective pressure sensor 18 providing feedback signal from the engine. The crank angle value at which a predetermined proportion of heat of available combusting fuel is released is obtained by utilizing the pressure measurement from the cylinder. The timing controller may be provided with a reference pressure curve map of the cylinder and measured pressure of the cylinder can indicate the crank angle of the monitored heat release timing. The heat release timing provided based on the measured pressure is compared with a nominal heat release timing, and it is determined whether the heat release timing is before or after the nominal heat release timing. The ignition timing is retarded in case of the heat release timing is before the nominal heat release timing, or advanced in case of the heat release timing is after the nominal heat release timing. [0034] Alternatively, the crank angle value at which a predetermined proportion of heat RQ of available combusting fuel Q _fuei is released can be obtained making use of measured pressure from the cylinder, over a crank angle range beginning from start of combustion to the angle where the predetermined proportion of heat RQ of available combusting fuel has been released, using an equation

With measured pressure and setting the RQ as desired. Advantageously the proportion of heat RQ is 15-50%, and preferably 15 - 25%.

[0035] The computer controller 102 comprises further a combustion phasing control unit 112 which is configured to provide a final set value for the computer control system which is transmitted to the charge ignition actuator 16. The final set value is obtained by adjusting the corrected set value provided by the summing unit 110.

[0036] In order make the control even more accurate the computer controller comprises means for generating a second feedback signal having a cylinder dependent control value concerning each one of the cylinders 12 of the engine 10. For that purpose, the computer controller 12 comprises cylinder-dedicated second control units 103.1 - 103.N. This means that the computer controller 12 comprises a second control unit 103 for each cylinder 12 of the engine 10. The control unit 103 for each cylinder is in data transfer communication with respective pressure sensor 18, as well as crank angle sensor 22, providing measurement signals from the engine.

[0037] Each one of the second control units 103 comprise a heat release determination unit 106.1 - 106.N, which is configured, and comprising an executable computer program, to determine a cumulative heat release Q by using measured pressure values from the cylinder, resulted from combustion of fuel over a crank angle range O ₀ - Si during which combustion of fuel is taken place, in one combustion cycle of the engine 10.

[0038] The heat release determination unit 106 for each cylinder is configured to operate as follows. The cumulative heat release is determined based on pressure measurement 18 from the cylinder of the engine 10 and using the crank angle measurement 20. The heat release is determined based on the pressure and known dimensions of the cylinder and the position of the piston, which can be derived from the actual crank angle position 28. dQ

[0039] A general formula for the heat release rate — in respect to a crank angle of an internal combustion piston engine is as follows dQ y dV , 1 .. dp

(1) — = — ■ p - 1 - V ■ — , dS y-1 dS y-1 dS

C _v where y is a heat capacity ratio — , p is pressure, V is volume of the cylinder, dV cv is change of volume in the cylinder, d8 is change of a crank angle and dp is change of pressure in the cylinder. For sake of clarity is should be noted that as a base unit of the heat release rate is J I crank angle degree.

Integrating the heat release rate equation (1) with respect to crank angle during which the combustion of fuel takes place in the cylinder, herein a range O ₀ -> Bi, one obtains a cumulative heat release Q, that is

[0040] For sake of clarity is should be noted that as a base unit of the cumulative heat release is Joule. This denotes the total heat which is released during the combustion of the fuel in the cylinder between the crank angle range O ₀ -> Bi. The computer control system 100 reads or otherwise obtains necessary information from the engine 10 to calculate the cumulative heat release Q _Cy n, Qc _y i2 ... Qcyin for each cylinder 12 of the engine 10. Pressure is measured from each cylinder 12 of the engine independently during combustion of fuel in the cylinder 12 at determined crank angles within a crank angle range O ₀ - Bi. The range represents the combustion phase in the cylinder; thus the cumulative heat release is determined from combustion of fuel over the crank angle range O ₀ - Si during which combustion of fuel is taken place in one combustion cycle in one cylinder of the engine.

[0041] The computer controller 103 comprise further a heat release rate determination unit 104.1-104. N which is configured, and comprising an executable computer program, to determine a mean gross heat release rate Q’ resulted from combustion of fuel, by providing a linear fitting to the cumulative heat release Q, a slope of which stands for the mean gross heat release rate Q’.

[0042] More precisely, the heat release rate determination unit 104 for each cylinder is configured to operate as follows. The mean gross heat release rate Q’ _Cy n , Q’c _y i2 ... Q’cyin of the combustion is determined from the cumulative heat release Qc _y n, Qc _y i2 ... Qcyin outcome. The mean gross heat release rate is obtained by providing a linear fitting to the cumulative heat release Q, a slope of which stands for the mean gross heat release rate Q’. An advantageous method of providing the linear fitting is the Least Square Regression Line method. Figure 3 shows an example of the cumulative heat release Q during one combustion cycle in a cylinder of an internal combustion piston engine by a dotted line therein. The horizontal axis depicts crank angle position in degrees, where 0 degrees corresponds to the top dead center of the piston in the cylinder. The vertical axis is the heat release in units of kJ. The solid line Q’ depicts the linear fitting to the cumulative heat release Q, the slope of which representing the mean gross heat release rate Q’ of the combustion. In the example of the figure 3 the mean gross combustion rate is approximately 2,2 kJ/degrees of crank angle.

[0043] The computer controller 103 comprise further a heat release rate controller 108.1-108. N which is configured to convert the mean gross heat release rate Q’ into a feedback signal having the second feedback value. The heat release rate controller 108 is advantageously configured to compare the mean gross heat release rate Q’ to a nominal gross heat release rate Qn’ value at the monitored engine load, and in case the mean gross heat release rate Q’ is smaller than the nominal gross heat release rate Qn’, the second feedback value is increased, and in case the mean gross heat release rate Q’ is greater than the nominal gross heat release rate Qn’ the second feedback value is decreased, from a feedback value for the nominal gross heat release rate Qn’. [0044] The computer controller comprises further a summing unit 110 in which the set value provided by the first control unit 114 and the second feedback value provided by the second control unit 103 are combined providing a corrected set value for the computer control system.

[0045] When a multi-cylinder internal combustion piston engine 10 is operated under control of the computer control system 100 in the method of controlling phasing of combustion of fuel at least the following steps are executed. Engine speed is measured by means of the crank angle /speed sensor 20 and engine load is determined by the load detecting means 22 as first measures of the method. These may take place by utilizing direct measurement of one or more variables of the engine and optionally using a computer model or simulation. The monitored speed and load are utilized in the first control unit 114 which provides a set value for controlling the phasing of combustion. The first control unit and method utilizes a predefined combustion phasing map, which is stored or made available to the computer control system 100. The map provides a control value which is based on current speed and load of the engine for controlling the charge ignition actuator 16. The set value can be considered as a global setpoint for combustion phasing concerning all the cylinder of the engine 10. The phasing is timing of the combustion process in respect to the position of the piston in the cylinder. The set value resulted from the method step is thus common for all the cylinders of the engine.

[0046] The method comprises further a step of determining a first feedback value for use in the combustion phasing control unit 112 of the computer control system 100, which is a task of the timing controller 116. In the step 1160 a crank angle value at which a predetermined proportion of heat RQ of available combusting fuel released is determined by using measured pressure values 180 from the cylinder 12, as is explained above in connection with description of the timing controller 116. Thus, in the method step 1120 the corrected set value obtained from the summing unit 110 and the first feedback value obtained from the step 1160 are converted into suitable control signal and value for controlling the cylinder-wise phasing of combustion fuel. [0047] Measuring pressure in each cylinder is practised for obtaining actual pressure value in the cylinder in relation to respective crank angle value, which also represent the respective position of the piston in the cylinder. The crank angle measurement is advantageously provided since engine speed is a speed of change of angular position of crank shaft of the engine. Measured pressure and respective crank angle of the engine are used in determining a cumulative heat release Q in the heat release determination unit 106. The cumulative heat release Q is determined by using measured pressure values from the cylinder, the pressure resulted from combustion of fuel over a crank angle range O ₀ - Si during which combustion of fuel is taken place, in one combustion cycle of the engine 10.

[0048] Next, a mean gross heat release rate Q’ci, Q’c2 ... Q’cn of the combustion is determined for each cylinder in the unit 104, from the cumulative heat release Qci , QC2 . .. Qcn outcome. That can be obtained by providing a linear fitting to the cumulative heat release Q, a slope of which stands for the mean gross heat release rate Q’. An advantageous method of providing the linear fitting is the Least Square Regression Line method. Figure 2 shows an example of the cumulative heat release Q during one combustion cycle in a cylinder of an internal combustion piston engine by a dotted line therein. The horizontal axis depicts crank angle position in degrees, where 0 degrees corresponds to the top dead center of the piston in the cylinder. The vertical axis is the heat release in units of kJ. The solid line Q’ depicts the linear fitting to the cumulative heat release Q, the slope of which representing the mean gross heat release rate Q’ of the combustion.

[0049] In the next step performed by the unit 108, the obtained mean gross heat release rate Q’ is converted into suitable control signal and value. This is advantageously practised by comparing the mean gross heat release rate Q’ to a nominal gross heat release rate Qn’ value at the monitored engine load, and in case the mean gross heat release rate Q’ is smaller than the nominal gross heat release rate Qn’, the control value is increased, and in case the mean gross heat release rate Q’ is greater than the nominal gross heat release rate Qn’ the control value is decreased, from a second feedback value for the nominal gross heat release rate Qn’. [0050] Next the global set value obtained from the unit 114 and the second feedback value obtained from the unit 108 are combined or summarized in the unit 110 which results in a corrected set value for use in in the combustion phasing control unit 112 together with the first feedback value.

[0051] The method can be implemented by a computer program stored in a readable memory device 101 , by executing the program by the computer controller of the multi-cylinder internal combustion piston engine.

[0052] Figure 3 shows an exemplary trend graph of the mean gross heat release rate over 200 consecutive engine cycles in one cylinder. As can be seen, there may be some variation in the combustion circumstance. Therefore, according to an embodiment of the invention cylinder specific mean gross heat release rate Q’ values of successive combustion cycles are provided, from each one of the cylinders 12 of the engine 10 and an average value of the cylinder specific mean gross heat release rate Q’ values is calculated for use in providing the second feedback value.

[0053] While the invention has been described herein by way of examples in connection with what are, at present, considered to be the most preferred embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but is intended to cover various combinations or modifications of its features, and several other applications included within the scope of the invention, as defined in the appended claims. The details mentioned in connection with any embodiment above may be used in connection with another embodiment when such combination is technically feasible.