Technical field

[001 ] The present invention relates to a method of detecting an angle of start of ignition in an internal combustion piston engine according to the preamble of claim 1 .

[002] Invention relates also to a control arrangement for controlling an internal combustion engine comprising a control unit for controlling the operation of the engine, and an ignition detection module according to preamble of independent control arrangement claim.

Background art

[003] Ignition of fuel in a combustion chambers of an internal combustion piston engine may be initiated in principal by auto-ignition, where the fuel ignites caused by the circumstances in the combustion chamber, and by making use of an external ignition or heat source, such as spark ignition, pilot fuel injection or laser ignition, where the fuel ignites caused by externally triggered ignition.

[004] A spark ignition system typically includes ignition coils which comprise primary windings and secondary windings and by which voltage transformation is implemented for the operation of a spark plug. The secondary voltage is distributed to spark plugs, which provides sparks across their gaps. The spark ignite mixture of air and fuel in cylinders and the mixture is combusted which cause thus generated pressure in the cylinder to force a piston to move and thus the combustion produce mechanical power.

[005] Regardless of the method of implementing an external ignition, the timing of the ignition is important. The duration in crank angle de- grees that the fuel takes to burn will increase somewhat with engine speed. This means that the faster the engine runs the earlier the spark has to occur. By retarding the ignition timing maximum cylinder pressures will be reduced, which can reduce some pollution formation and eliminate knocking if that is a problem. However, the retarded ignition timing will also reduce thermal efficiency of the engine and thereby increase fuel consumption.

[006] For example in WO201 1023852 A1 there is described a method in connection with a reciprocating combustion engine with at least two cylinders. In the method of a reciprocating combustion engine with at least two cylinders, in which engine ignition energy is provided to spark plugs for generating sparks suitable for firing in combustion chambers, in which the method comprising steps of generating a secondary voltage to the spark plugs from a primary voltage supply, determining a spark diagnostic value indicative of a secondary voltage demand separately for each spark plug during the engine is in operation, adjusting ignition timing of the spark plug, whose spark diagnostic value exceeds a offset threshold, by advancing the ignition timing of the spark plug to engine angular position where a combustion chamber pressure is lower.

[007] US 4070613 shows an apparatus for measuring the ignition timing of a multi-cylinder internal combustion engine of the type having a pulse generator for indicating when the flywheel is in a predetermined position with respect to top dead center and in which an input signal is obtained from one particular spark plug and employed to initiate a counting operation employing a series of pulses which have a definite frequency rela- tionship to the speed of the engine. [008] Typically a flywheel or a crankshaft of the engine is provided with a reference indicator by means of which the position of the crankshaft and thus also the positions of each piston and other parts coupled to the crankshaft may be defined. In US 6192861 there shown an ignition de- vice for an engine, where a protrusion provided on a flywheel mounted on a crankshaft is revolved with the rotation of the crankshaft. A magnet pickup detects the passage of the protrusion. When the protrusion passes near the magnet pickup, the magnet pickup outputs a detection signal, in a pulse manner, having a peak value in response to the passing speed of the protrusion. It is also know to arrange a cavity, such as a drilled hole on the flywheel for the purposes of identifying its angular position.

[009] Even if the control arrangements in combustion engines are manufactured with all due care, there may still emerge malfunction in provid- ing properly timed ignition command and there is a need to improve the reliability of the control of an engine.

[0010] An object of the invention is to provide a method of controlling an angle of start of ignition in an internal combustion piston engine by means of which the performance of the engine is considerably improved compared to the prior art solutions.

[001 1 ] It is also an object of the invention to provide a control arrangement for controlling an internal combustion piston engine by means of which the performance of the engine is considerably improved compared to the prior art solutions.

Disclosure of the Invention

[0012] In this connection the term angle is to be understood to mean an angular position of a crankshaft of the engine. The angular position may be expressed for example as degrees between 0° to 720° in four-stroke engines and 0° to 360° in two-stroke engines, the 0° representing a predetermined base position, which may be selected to be for example a top dead centre of a cylinder number 1 of the engine before a power stroke.

[0013] An object of the invention is substantially met by a method of con- trolling an angle of start of ignition in an internal combustion piston engine, wherein following steps are practised during the operation of the engine: a) a reference signal of a predetermined angular position of the crankshaft is acquired and a first time stamp is assigned to the acquired reference signal, b) a signal of timed start of ignition is generated, and a second time stamp is assigned to the signal of the start of the ignition, c) a signal indicating a speed of the engine is acquired, d) time elapsed between the first and the second time stamp is determined, e) a check angle value of start of ignition is acquired such that a product of the signal indicating the speed of the engine and the time elapsed between the first and the second time stamps is added to the known angular position of the reference signal, f) an ignition window is determined by having the check angle value as a base value of the window and providing a pre-set advancing margin and retarding margin, and by determining a lower value of the window by subtracting the advancing margin from the base val- ue and a lower value of the window by adding the pre-set retarding margin to the base value of the window, g) checking whether the timed start of ignition instruction generated by the control unit is within the ignition window, and h) providing a correction signal for use in generating the timed start of ignition signal. [0014] The reference signal is obtained by means of a predetermined indication of angular position of the crankshaft. The timing referred to above means also setting the occurrence to take place at certain position of the crankshaft and respectively each piston of the engine.

[0015] By means of the invention it is possible to improve the safety of the operation of the engine i.e. with the invention the risk of damage caused to the engine by improper timing of the ignition may be decreased.. By means of the invention the actual start of the ignition is each cylinder may be accurately determined and used in controlling the operation of the engine, hence improving the safe operation of the en- gine.

[0016] The signal indicating the speed of the engine can be converted as angle of rotation per time unit which may be used for defining the check angle value. The check angle value a is a hence a product of the signal indicating the speed (ω) of the engine and the time elapsed between the first and the second time stamps added to the known angular position of the reference signal. So, the detection window is based on the check angle value and allowed advancing (- angle) and allowed retarding (+ angle) in respect to the base angle value i.e. the check angle value.

[0017] According to an embodiment of the invention the used speed of the engine is determined as mean value during one occurrence of acquiring the reference signal.

[0018] According to another embodiment of the invention the used speed of the engine is determined as mean value over two or more occurrences of acquiring the reference signal. This increases the accuracy of the speed of the engine signal.

[0019]

[0020] Next, the result of the comparison of the timed start of the ignition with the ignition window is utilized such that an inaccurate ignition start- flag shall be set for the engine control unit if the signal of the timed start of the ignition is not within the ignition window.

[0021 ] According to an embodiment of the invention, in case that the signal of the timed start of the ignition is not acquired at all, a missing start of ignition-flag is set for the engine control unit. [0022] Thus generated inaccurate ignition start- flag and missing start of ignition-flag may be used for control actions by the control unit of the engine for use in connection with procedure relating to the forced start of ignition. [0023] According to an embodiment of the invention the reference signal is acquired at least once during a rotation of the crankshaft.

[0024] According to another embodiment of the invention the reference signal is acquired more than once during a rotation of the crankshaft but less frequent than the signal of timed start of ignition is generated. [0025] The signal of timed start of ignition is generated for each ignition occurrence of the engine.

[0026] According to an embodiment of the invention the reference signal of a predetermined angular position of the crankshaft is determined using source of information independent from the source of information used for generating the a signal of timed start of ignition.

[0027] The method can be further enhanced by following features. According to an embodiment of the invention the ignition window is determined, which means a range of angle for each cylinder of the engine within which the actual start of the ignition is to be taken place in order to be acceptably timed in respect to the combustion cycle.

[0028] This embodiment comprises a step of forced start of the ignition in case either the inaccurate ignition start- flag or the missing start of ignition-flag are set and some additional terms are fulfilled. In other words, this is the case if the actual start of the ignition is detected but not within the ignition window or the actual start of the ignition is not detected. Naturally, the forced start of ignition operation may be enabled or disabled by the control unit and/or manually. [0029] According to an embodiment of the invention it is determined if the signal of timed start of ignition is before the ignition window, and if that is the case, then the signal of timed start of ignition is ignored in the further control process of the engine, and a forced start of ignition is initiated af- ter the ignition window has been passed.

[0030] It is further determined if the signal of timed start of ignition is before the ignition window, and if that is not the case, then it is determined if the signal of timed start of ignition is within the ignition window, and if that is not the case, then the signal of start of the ignition is ignored in the further control process of the engine, and a forced start of ignition is initiated after the ignition window has been passed.

[0031 ] In the method it is further determined if the signal of timed start of ignition is before the ignition window. If that is not the case i.e. If the angle of actual start of the ignition actually is detected and determined not to be before the ignition window, then it is determined if the signal of timed start of ignition is within the ignition window. And, if that is the case, the control is set to the next cylinder coming to start of ignition phase.

[0032] With the forced start of ignition it is ensured that the combustion takes places adequately even if the start of the ignition controlled by the control unit has been take place before or after the ignition window for some reason or even in the case that the signal of timed start of ignition is not generated at all.

[0033] Object of the invention is met also by a control arrangement for controlling an internal combustion engine comprising a control unit for controlling the operation of the engine, and an ignition detection module which comprises a) executable instructions to acquire a reference signal of a predetermined angular position of the crankshaft and to assign a first time stamp to the acquired reference signal, b) executable instruction to generate a signal of tinned start of ignition, and to assign a second time stamp to the signal of the start of the ignition, c) executable instructions to acquire a signal indicating a speed of the engine, d) executable instructions to determine time elapsed between the first and the second time stamp, e) executable instructions to acquire a check angle value of start of ignition such that a product of the signal indicating the speed of the engine and the time elapsed between the first and the second time stamps is added to the known angular position of the reference signal, f) executable instructions to determine an ignition window by having the check angle value as a base value of the window and providing a pre-set advancing margin and retarding margin, and by determining a lower value of the window by subtracting the advancing margin from the base value and a lower value of the window by adding the pre-set retarding margin to the base value of the window, g) executable instructions to check whether the timed start of ignition instruction generated by the control unit is within the ignition window, and h) executable instructions to provide a correction signal for use in generating the timed start of ignition signal in the control unit of the engine.

[0034] According to an embodiment of the invention the ignition detection module comprises executable instructions to acquire the reference signal during a rotation of the crank-shaft.

[0035] According to an embodiment of the invention the ignition detection module comprises executable instructions to generate the signal of timed start of ignition for each ignition occurrence of the engine. [0036] According to an embodiment of the invention the control arrangement comprises an auto-ignition module which is provided with executable instructions to determine if the signal of timed start of ignition is before the ignition window, and if that is the case, then ignore the signal of timed start of ignition in the further control process of the engine, and in i- tiate a forced start of ignition after the ignition window has been passed. [0037] According to an embodiment of the invention the control arrangement comprises an auto-ignition module which is provided with executable instructions to determine if the signal of timed start of ignition is before the ignition window, and if that is not the case, then to determine if the signal of timed start of ignition is within the ignition window, and if that is not the case, then to ignore the detected actual start of the ignition in the further control process of the engine, and initiate a forced start of ignition after the ignition window (W) has been passed.

[0038] According to an embodiment of the invention the control arrange- ment comprises an auto-ignition module which is provided with executable instructions to determine if the signal of timed start of ignition is before the ignition window, and if that is not the case, then to determine if the signal of timed start of ignition is within the ignition window, and if that is the case, then setting the control to the next cylinder coming to start of ignition phase.

[0039] The signal indicating the speed of the engine may be calculated by the ignition detection module or it may be acquired via communication channel from engine control unit.

[0040] According to a specific embodiment of the invention the method is adapted for control a spark ignited engine, in which case the start of the ignition means occurrence of ignition spark.

[0041 ] Respectively according to a specific embodiment of the invention the control arrangement is adapted to a spark ignited engine.

The ignition detection module and the auto-ignition module can be sepa- rate modules or integrated with each other and also with the control unit of the engine.

Brief Description of Drawings [0042] In the following, the invention will be described with reference to the accompanying exemplary, schematic drawings, in which

Figure 1 illustrates an ignition diagram of an eight cylinder engine according to an embodiment of the invention,

Figure 2 illustrates a flow chart of a method according to another embodiment of the invention,

Figure 3 illustrates an ignition diagram illustrating a method according to another embodiment of the invention,

Figure 4 illustrates an ignition diagram illustrating another aspect of method according to another embodiment of the invention, and

Figure 5 illustrates an internal combustion engine provided with a control arrangement according to an embodiment of the invention.

Detailed Description of Drawings

[0043] Figure 1 shows an ignition diagram by means of which the method according to an embodiment of the invention can be illustrated in exemplary manner. Considering that the example relates to a four stroke en- gine provided with 8 cylinders, each cylinder 1 - 8 is ignited once during two revolutions of the crankshaft and therefore the full cycle in figure 1 represents to 720° of crank angle. The numbers of cylinders 1 - 8 are here in the sequence of ignition, not as they are physically arranged in line or other configuration.

[0044] With the method of controlling an angle of ignition in an internal combustion piston engine it is possible to improve the proper timing the actual start of the ignition as meant be based on the control instructions of a control unit of the engine.

[0045] Actual positions of the signal of start of ignition of each cylinder are shown by arrows 10 in the figure. In this example only the third ignit- ed cylinder is studied in more detailed manner. Firstly, as there is at least one reference indicator mark arranged (shown with reference number 5 in Figure 5) to the crankshaft or the flywheel the movement which reference indicator is detected e.g. by the control unit of the engine or by a separate ignition detection module, a reference signal R of is acquired which provides the ignition detection module with information of actual crank angle once per revolution of the crankshaft. The actual location of the reference point does not have to be any exact point as long as it is at a known predetermined position and the location may even be changed or there may be more than one reference indicator marks arranged in the engine. A first time stamp t _R is assigned to the acquired reference signal R so that the moment of the occurrence is known. Signal of timed start of ignition is generated and a second time stamp t, is assigned to the signal of the start of the ignition. [0046] A signal of timed start of ignition is generated and a second time stamp ti is assigned to the signal. This signal is or represents the signal created in response to an actual timed start of ignition generated by the engine control unit based on which the ignition is triggered in a certain cylinder of the engine. [0047] Further, the time elapsed At between the first t _R and the second time stamp t, is determined. Also, a signal indicating a speed ω of the engine is acquired.

[0048] Next a checking procedure is practised resulting in a check angle value (a) which is used to check if the actual timed start of ignition is pro- vided with desired timing. This involves acquiring the check angle value (a) of start of ignition such that a product of the signal indicating the speed ω of the engine and the time elapsed At between the first and the second time stamps is added to the known angular position of the reference signal R. The check angle value is used as a base value for deter- mining an ignition window w. The ignition window W is determined by having the check angle value as a base value of the window W and providing a pre-set advancing margin and retarding margin, and by determining a lower value of the window by subtracting the advancing margin from the base value and a lower value of the window by adding the pre-set retarding margin to the base value of the window.

[0049] Next it is checked if the actual timed start of ignition instruction 10 generated by the control unit is within the ignition window w. In the figure 1 it can be seen that the actual timed start of the ignition instruction 10 is later than the check angle value (a) but still within the ignition window w. [0050] In the method a correction signal is provided for use in generating the timed start of ignition signal. The correction signal is provided based on check angle value a of start of ignition and/or the ignition window w.

[0051 ] The signal indicating the speed of the engine can be converted as angle of rotation per time unit which may be used for defining the check angle value a. The check angle value a is hence a multiple of the signal indicating the speed and time the time elapsed between the first and the second time stamps. The correction signal of the ignition may be transmitted to or made available to the control unit of the engine to be used in further control procedures performed by the control unit making it possi- ble to operate the engine even more accurately.

[0052] The ignition window w is defined by a pre-set start angle and a pre-set end angle of the ignition window. These are defined by making use of an advancing margin and a retarding margin which are set according to the application. The advancing margin and the retarding mar- gin may be also set to be a function an operational parameter of the engine, such as engine load.

[0053] Now according to an embodiment of the invention after the signal of timed start of the ignition is generated, said angle is compared with the ignition window W. More particularly, there is a step of determining whether the tinned start of ignition instruction generated by the control unit is within the ignition window.

[0054] Next, the result of the comparison of the angle of the timed start of the ignition with the ignition window is utilized such that an inaccurate ignition start- flag shall be set for the engine control unit if the actual angle is not within the ignition window.

[0055] According to an embodiment of the invention, in case that the signal of the timed start of the ignition is not acquired at all, a missing start of ignition-flag is set for the engine control unit for use in connection with procedure relating to the forced start of ignition according to an embodiment of the invention.

[0056] Thus generated inaccurate ignition start- flag and missing start of ignition-flag may be used for control actions by the control unit of the engine. [0057] Figure 2 illustrates a flow chart illustrating the method according to an embodiment of the invention. In the method after the start 100 the angle of the timed start of the ignition is acquired in step 101 . It is a prerequisite that an ignition window is determined, which means a range of crank angle for each cylinder of the engine within which the actual start of the ignition is to be taken place in order to be acceptably timed in respect to the combustion cycle. The ignition window is preferably determined as is described above but in order to practise this embodiment of the invention the way of determining the ignition window may also be different. [0058] Once the signal of timed start of the ignition 10 has been generated a comparison is made whether the timed start of the ignition is taken place before the ignition window w. This is depicted by the decision step 102. In case the timed start of the ignition is not timed to be taken place before the ignition window w, next a comparison is made whether the timed start of the ignition 10 is taken place within the ignition window w. This is depicted by the decision step 103. If that is the case, meaning that the engine control unit has generated the start of ignition signal with proper timing and the control is set to the next cylinder in firing order, step C=C+1 and the process is started over again 100.

[0059] In case the decision in step 102 is positive i.e. the timed start of the ignition 10 is taken place before the ignition window W, the actual start of ignition signal is ignored by the engine control unit in its further processing. This is depicted by the step 104. Next, in the step 105 a forced start of ignition is practised after the next ignition window has passed. Next, the control set to the next cylinder in firing order, step C=C+1 and the process is started over again 100.

[0060] In case the timed start of the ignition is not set to take place within the ignition window w in step 103, the actual start of ignition is ignored by the engine control unit in its further processing. This is depicted by the step 104. Next, in the process step 105 the forced start of ignition is practised after the ignition window has passed. Next, the control set to the next cylinder in firing order, step C=C+1 and the process is started over again 100. [0061 ] In the Figure 3 this procedure is illustrated with a reference to an ignition diagram. Considering that it relates to a four stroke engine each cylinder 1 - 8 is ignited once during two revolutions of the crankshaft and therefore the full cycle in figure 3 represents to 720° of crank angle. In case of a two stroke engine the full cycle would represent 360° of crank angle. The numbers of cylinders 1 - 8 are also here in the sequence of ignition or firing, not as they are physically arranged in line, or other configuration.

[0062] In figure 3 the signal of timed start of injection in each of the cylinder during one cycle is depicted with arrows 10. The ignition window W is determined which is shown by the sector W. Between the end of a preceding ignition window W and the beginning of a prospective window W there is an intermediate angle range W representing an angle range where the start of the ignition is either too early or too late. Now, in the figure 3 it is shown, as an example how the timing of the start of the ignition 10' of cylinder 2 is late based on the signal. For that reason, the timed start of the ignition has not been detected within the ignition window of cylinder 2. So, according to decision step 103 of figure 2, the signal start of ignition is ignored by the engine control unit in its fur- ther processing. This is depicted by dotted line of the arrow 10'. Instead, the forced start of ignition is generated which is timed to trigger the start of ignition immediately after the ignition window W has passed, which is depicted by the arrow 10" in the figure 3. This should be understood that the forced start of ignition is practised when the crank angle is greater than upper range of the ignition window W. Next, the control set to the next cylinder in firing order, i.e. cylinder 3 in this case. In figure 4 there is shown an example of a situation where the timing of the start of the ignition 10' of cylinder 3 is early. So, according to the decision step 102, which is positive i.e. the timed start of the ignition is timed before the igni- tion window W, the actual start of ignition is ignored by the engine control unit in its further processing. This is depicted by dotted line of the arrow 10'. Next, the forced start of ignition is generated which is timed to trigger the start of ignition immediately after the ignition window W has passed, which is depicted by the arrow 10" in the figure 4. Next, the control set to the next cylinder in firing order i.e. cylinder number 4 in this case.

[0063] Figure 5 depicts schematically an internal combustion engine 200 which is provided with an external ignition system such as a spark ignition system. The engine is provided with a control arrangement 202 for controlling the engine. The control arrangement 202 comprises a control unit 204 which is arranged to control the operation of the engine 200 including controlling the operation of the external ignition system. Engine 200 has ignition means 208 connection with each cylinder 210 of the engine 200.The ignition means 208 are arranged in control communication with the control arrangement 202 of the engine 200

[0064] The control arrangement 202 for controlling an internal combus- tion engine 200 comprises also an ignition detection module 206 which comprises executable instructions to acquire a reference signal R of a predetermined angular position of the crankshaft and to assign a first time stamp t _R to the acquired reference signal. This way the actual angular position of the crankshaft is made available to the control system for checking purposes.

[0065] The ignition detection module 206 comprises also executable instruction to generate a signal of timed start of ignition, and to assign a second time stamp t, to the signal, and to acquire a signal indicating a speed ω of the engine. The ignition detection module 206 further com- prises executable instructions to determine time elapsed At between the first and the second time stamp, and instructions to acquire a check angle value a of start of ignition such that a product of the signal indicating the speed ω of the engine and the time elapsed At between the first and the second time stamps is added to the known angular position of the reference signal R. The ignition detection module 206 comprise also executable instructions to determine an ignition window W by having the check angle value as a base value of the window W and providing a preset advancing margin and retarding margin, and by determining a lower value of the window by subtracting the advancing margin from the base value and a lower value of the window by adding the pre-set retarding margin to the base value of the window.

[0066] And further, the ignition detection module 206 comprises executable instructions to check whether the timed start of ignition instruction generated by the control unit is within the ignition window w, and execut- able instructions to provide a correction signal for use in generating the tinned start of ignition signal.

[0067] According to an embodiment of the invention the ignition detection module 206 comprises executable instructions to acquire the reference signal R one during one rotation of the crank-shaft.

[0068] The ignition detection module (206) comprises executable instructions to generate the signal of timed start of ignition for each ignition occurrence of the engine.

[0069] The arrangement can be further enhanced by following features. The control arrangement is according to a further embodiment of the invention provided with executable instructions to initiate a start of the ignition in case either the inaccurate ignition start- flag or the missing start of ignition-flag are set for the control unit 204 or the arrangement 202. This is that case where the signal of timed start of the ignition is detected but not within the ignition window or the start of the ignition signal is not detected at all for some reason.

[0070] According to an embodiment of the invention the control arrangement 202 comprises in addition to the control unit 204 and the ignition detection module 206, an auto ignition module 212 which is provided with executable instructions for controlling a forced start of the ignition in case either the inaccurate ignition start- flag or the missing start of ignition-flag are set and some additional terms are fulfilled.

[0071 ] More specifically the auto ignition module 212 comprises executable instructions to determine if the signal of timed start of ignition is be- fore the ignition window w, and if that is the case, then ignore the signal of timed start of ignition in the further control process of the engine, and initiate a forced start of ignition after the ignition window W has been passed. [0072] The auto-ignition module 212 is additionally provided with executable instructions to determine if the signal of timed start of ignition is before the ignition window, and if that is not the case, then to determine if the signal of timed start of ignition is within the ignition window w, and if that is not the case, then to ignore the detected actual start of the ignition in the further control process of the engine, and initiate a forced start of ignition after the ignition window W has been passed.

[0073] The auto-ignition module 212 is further provided with executable instructions to determine if the signal of timed start of ignition is before the ignition window, and if that is not the case, then to determine if the signal of timed start of ignition is within the ignition window w, and if that is the case, then setting the control to the next cylinder coming to start of ignition phase. The control unit, the auto ignition and the ignition detection module may be for example suitable computer hardware to execute the instructions. If communication is lost between the units, the operation of the auto ignition module is disabled immediately. That is because for example the speed information is no longer available the ignition window may become invalidly positioned..

[0074] 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.