Patent Grant
10865719
The present disclosure relates to a detection method for detecting a knocking occurrence state in an internal combustion engine. The present disclosure further relates to an ignition timing control method of appropriately controlling the ignition timing of the internal combustion engine in accordance with the knocking occurrence state detected by the detection method, and a control system that controls the ignition timing of the internal combustion engine by using the ignition timing control method.
Generally, the earlier the ignition timing in each combustion cycle is, the efficiency of the internal combustion engine increases. However, an earlier ignition increases the risk of occurrence of knocking due to abnormal combustion in a combustion chamber. Knocking refers to self-ignition of end gas that remains non-combusted in the combustion chamber after ignition, and such self-ignition produces impact wave that breaks a thermal boundary layer formed on the inner wall surface of the combustion chamber. Accordingly, the surface temperature of the inner wall surface of the combustion chamber increases excessively, which may cause damage to the combustion chamber. Thus, to operate the internal combustion engine as efficiently as possible while avoiding damage to the internal combustion engine due to knocking as much as possible, it is desirable to control the ignition timing of the internal combustion engine appropriately on the basis of the trade-off relationship between improvement of the efficiency of the internal combustion engine and a decrease in the knocking frequency.
For this, it is important to detect the knocking occurrence state in the combustion chamber of the internal combustion engine as accurately as possible. Patent Document 1 described below discloses a knocking detection method. As described in Patent Document 1, a typically-used evaluation index of knocking strength is knocking severity. However, in many cases, a knocking detection result detected from the knocking severity contradicts with typical knocking characteristics that are actually observed.
Patent Document 1 discloses a knocking detection method that is more advantageous than detection based on knocking severity, which is a knocking determination method capable of detecting of a serious knocking that may damage the combustion chamber considerably at an early stage. Specifically, Patent Document 1 discloses a knocking determination method including the following determination process. First, a knocking time window and a band-pass filter are used to extract a waveform signal of a knocking frequency from measurement data of inner pressure or acceleration obtained by a sensor disposed in the combustion chamber, and the first calculation value is obtained by integration. Next, a reference time window and a band-pass filter are used to extract a waveform signal of a reference frequency from the above measurement data, the second calculation value is obtained by integration, and a reference average value is obtained from moving average over a plurality of combustion cycles. The first calculation value obtained as described above is divided by the reference average value to obtain a S/N ratio, which is weighted by a weight coefficient, and moving average is obtained over a plurality of combustion cycles. Accordingly, a knocking index is calculated, on the basis of which presence or absence of knocking is determined.
However, from the perspective of detecting occurrence of knocking at a highest possible accuracy, the knocking determination method in Patent Document 1 fails to appropriately select the time range for setting the knocking time window and the reference time window on a reasonable basis. This will be described below in detail.
The above described S/N ratio indicates the relative magnitude of the index value obtained from the knocking frequency waveform in a knocking occurrence period, as compared to the moving average of the index value obtained from the frequency waveform in a period without knocking. Thus, to achieve a highly accurate correlation of the above described S/N ratio and the knocking occurrence risk, the knocking time window should include only the time range with a high risk of occurrence of knocking without omission. On the other hand, the reference time window should be set so as to include only the time range with a minimum risk of occurrence of knocking. However, in the knocking determination method in Patent Document 1, the knocking time window is set to match the combustion period of the combustion chamber, but is not set to include only the time range with a high risk of occurrence of knocking without omission. Furthermore, in the knocking determination method in Patent Document 1, the reference time window is set so as to include a non-combustion period of the combustion chamber, but is not set to include only the time range with a minimum risk of occurrence of knocking.
In view of the above problem, an object of some embodiment of the present invention is to provide a knocking detection method capable of knocking detection with a higher accuracy, by selecting the setting range of the time window corresponding to a knocking occurrence period and the time window corresponding to a period without knocking appropriately on a reasonable basis. Furthermore, an object of some embodiments of the present invention is to provide an ignition timing control method of appropriately controlling the ignition timing of the internal combustion engine in accordance with the knocking occurrence state detected by the knocking detection method, and a control system that controls the ignition timing of the internal combustion engine by using the ignition timing control method.
(1) According to some embodiments of the present invention, a knocking detection method of detecting occurrence of knocking in a combustion chamber of an internal combustion engine includes: a step of obtaining an oscillation waveform generated by combustion of air-fuel mixture in the combustion chamber; a step of setting a first time window preceding a maximum inner pressure time at which an inner pressure of the combustion chamber is at maximum in a single combustion cycle and a second time window immediately after the maximum inner pressure time, and transforming each of a first waveform portion included in the first time window and a second waveform portion included in the second time window into an expression-domain expression, of the oscillation waveform; and a step of setting a first frequency window and a second frequency window, calculating a first representative value which is a representative value of the frequency domain expression of the first waveform portion in the first frequency window and a second representative value which is a representative value of the frequency domain expression of the second waveform portion in the second frequency window, and determining whether knocking has occurred on the basis of a relationship between the second representative value and the first representative value.
In the method shown in
Further, in the above method (1), the risk of occurrence of knocking is evaluated on the basis of two representative values obtained from the frequency domain expressions of two respective waveform portions included in the second time window and the first time window, respectively, from the oscillation waveform generated by combustion of air-fuel mixture. As a result, with this method (1), it is possible to evaluate the risk of occurrence of knocking while relatively comparing a representative value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period to a representative value of the frequency spectrum obtained from the oscillation waveform in a period without knocking. Therefore, according to the above method (1), the setting range of the time window corresponding to a knocking occurrence period and the setting range of the time window corresponding to a period without knocking are selected appropriately on a reasonable basis, and thereby it is possible to detect knocking with a higher accuracy.
(2) According to an illustrative embodiment of the present invention, the first representative value includes a first peak value at which an amplitude of the frequency domain expression of the first waveform portion is at maximum in the first frequency window. The second representative value includes a second peak value at which an amplitude of the frequency domain expression of the second waveform portion is at maximum in the second frequency window. The step of determining whether knocking has occurred includes determining whether knocking has occurred on the basis of a relationship between the second peak value and the first peak value.
According to the above method (2), when obtaining a representative value of the frequency domain expression, by using the peak value of a frequency spectrum curve corresponding to the frequency domain expression as a representative value, it is possible to obtain a representative value at a high speed through simple calculation. Thus, according to the above method (2), the process of determining whether knocking has occurred can be performed at a high speed with a low calculation load.
(3) In an illustrative embodiment of the present invention, in the above method (1), the first representative value includes a first partial overall (POA) value which is a POA value calculated from the frequency domain expression of the first waveform portion in the first frequency window. The second representative value includes a second POA value which is a POA value calculated from the frequency domain expression of the second waveform portion in the second frequency window. The step of determining whether knocking has occurred includes determining whether knocking has occurred on the basis of a relationship between the second POA value and the first POA value.
According to the above method (3), when obtaining a representative value of the frequency domain expression, a partial overall (POA) value of a frequency spectrum curve corresponding to the frequency domain expression is used as a representative value. A POA value is obtained by calculating the power spectrum of the frequency domain expression, calculating the power spectrum density on the basis of the calculated power spectrum, and calculating the square sum of the power spectrum density near the knocking frequency. Thus, when obtaining a representative value of the frequency domain expression, by using the POA value calculated as described above as a representative value, it is possible to obtain a representative value taking account of all of the frequency components near the knocking frequency in the frequency domain expression. Thus, according to the above method (3), in the process of determining whether knocking has occurred, it is possible to use a representative value taking account of all of the frequency components near the knocking frequency in the frequency domain expression.
(4) In an illustrative embodiment according to the present invention, in the above methods (1) to (3), the first frequency window and the second frequency window are selected so as to include a frequency component which appears as a peak frequency, of a frequency component of an impact wave generated in the combustion chamber due to knocking occurrence.
According to the above method (4), the first frequency window and the second frequency window are set so as to always include a frequency component that appears as a peak frequency, from among frequency components of the impact wave generated in the combustion chamber due to occurrence of knocking. As a result, the peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period and the peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking are extracted from a vicinity frequency range surrounding the peak frequency unique to the time of occurrence of knocking. Furthermore, the peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period and the peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking are extracted from a common peak vicinity frequency range. As a result, according to the above method (4), it is possible to evaluate the risk of occurrence of knocking even more accurately, by relatively comparing a peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period to a peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking.
(5) In an illustrative embodiment according to the present invention, in the above methods (1) to (4), the combustion chamber further comprises a precombustion chamber including an ignition plug disposed therein, and a main chamber in communication with the precombustion chamber via a nozzle hole, and wherein, in each combustion cycle of the internal combustion engine, the first window is set so as to include an ignition timing of the ignition plug.
In the above method (5), the above described first time window is set so as to include a timing of ignition of the ignition plug in the precombustion chamber. Herein, on ignition of the precombustion chamber, only a small amount of fuel gas for producing a torch exists in the precombustion chamber, and is directly ignited by the ignition plug. Thus, the risk of knocking due to abnormal combustion is extremely low. In addition, on ignition of the precombustion chamber, it is possible to observe the oscillation waveform due to combustion of air-fuel mixture while knocking is not occurring. Accordingly, it is possible to evaluate the risk of occurrence of knocking even more accurately, by comparing the peak values of two frequency spectra obtained from two waveform portions included in the first time window including the ignition timing of the precombustion chamber and the second time window corresponding to a knocking period, respectively.
(6) In an illustrative embodiment according to the present invention, in the above methods (1) to (5), transform of the first waveform portion or the second waveform portion into the frequency domain expression includes a process of transforming a time-series sample of the first waveform portion or the second waveform portion into a set including an amplitude value of each sampling frequency by fast Fourier transform (FFT).
In the above method (6), the transform of the first waveform portion or the second waveform portion into a frequency domain expression is performed by applying a fast Fourier transform (FFT) to a time-series sample of the first waveform portion or the second waveform portion. Thus, it is possible to provide a plurality of (K) converters corresponding to a plurality of (K) sampling frequencies on the frequency axis, and to perform the calculation process of discrete Fourier transform on a plurality of time-series samples in parallel by using the plurality of (K) converters of parallel configuration. As a result, it is possible to perform fast transform of the first waveform portion or the second waveform portion to the frequency domain expression. Accordingly, even in a case where the rotation speed of the crank shaft is extremely high and it is necessary to detect occurrence of knocking in an extremely short period of time for each combustion cycle, it is possible to perform the frequency domain transform for the first waveform portion or the second waveform portion with a high speed in such determination.
(7) In an illustrative embodiment according to the present invention, in the above methods (1) to (6), a cylinder constituting the combustion chamber in the internal combustion engine includes an inner pressure measurement device configured to measure and output an inner pressure variation waveform in the combustion chamber of the internal combustion engine. The oscillation waveform is extracted as a harmonic component from the inner pressure variation waveform in the combustion chamber of the internal combustion engine measured by the inner pressure measurement device, and the harmonic component includes an oscillation frequency component which is unique to the time of occurrence of knocking.
Of physical amounts that can be measured in the combustion chamber of the internal combustion engine, the physical amounts having the strongest correlation with knocking strength include variation of the inner pressure in the combustion chamber, and the acceleration measured from oscillation generated inside the combustion chamber. According to the above method (7), only by providing a simple inner pressure measurement device such as an in-cylinder pressure sensor, in the cylinder constituting the combustion chamber of the internal combustion engine, it is possible to obtain an oscillation waveform in the combustion chamber necessary for detection of knocking, from the inner pressure variation waveform in the combustion chamber measured by the inner pressure measurement device. At this time, in the above method (7), an oscillation frequency component that is unique to the time of occurrence of knocking is extracted from the measured inner pressure variation waveform. Accordingly, in the above method (7), it is possible to extract, from the measured inner pressure variation waveform, only the frequency component excluding the basic frequency component that varies synchronously with the advancement of the combustion cycle (each stage of combustion cycle), as the oscillation frequency component unique to the time of occurrence of knocking.
(8) In an illustrative embodiment according to the present invention, in the above methods (1) to (6), a cylinder constituting the combustion chamber in the internal combustion engine includes an acceleration sensor configured to detect and output an acceleration detection waveform in the combustion chamber of the internal combustion engine, and the oscillation waveform is obtained as the acceleration detection waveform detected by the acceleration sensor in the internal combustion engine.
Of physical amounts that can be measured in the combustion chamber of the internal combustion engine, the physical amounts having the strongest correlation with knocking strength include variation of the inner pressure in the combustion chamber, and the acceleration measured from oscillation generated inside the combustion chamber. In the above embodiment (8), only by providing the acceleration sensor having a simple configuration for the combustion chamber of the gas engine, it is possible to directly obtain an oscillation waveform corresponding to the oscillation frequency component unique to the time of occurrence of knocking, from the acceleration variation waveform measured by the acceleration sensor.
(9) According to some embodiments of the present invention, an ignition timing control method of controlling an ignition timing of ignition of air-fuel mixture in a combustion chamber of an internal combustion engine includes: a detection step of detecting presence or absence of occurrence of knocking in each combustion cycle for the ignition timing which is currently set; a correlation update step of calculating a variation trend, up to a present time, of a knocking occurrence frequency on the basis of a result of detection of the presence or absence of occurrence of knocking, and updating a correlation between a change in the ignition timing and the knocking occurrence frequency to the latest state; and an ignition timing control step of controlling the ignition timing of the internal combustion engine on the basis of the correlation. The detection step includes: obtaining an oscillation waveform which is generated by combustion of air-fuel mixture in the combustion chamber; setting a first time window preceding a maximum inner pressure time at which an inner pressure of the combustion chamber is at maximum in a single combustion cycle and a second time window immediately after the maximum inner pressure time, and transforming each of a first waveform portion included in the first time window and a second waveform portion included in the second time window into an expression-domain expression, of the oscillation waveform; and setting a first frequency window and a second frequency window, extracting a first representative value which is a representative value of the frequency domain expression of the first waveform portion in the first frequency window and a second representative value which is a representative value of the frequency domain expression of the second waveform portion in the second frequency window, and determining whether knocking has occurred on the basis of a relationship between the second representative value and the first representative value.
According to the above method (9), by a method similar to that in the above (1), it is possible to detect knocking occurrence of each combustion cycle accurately and to control the ignition timing so that the ignition timing of the internal combustion engine becomes optimum, on the basis of the knocking detection result of each combustion cycle. At this time, the earlier the ignition timing in each combustion cycle is, the efficiency of the internal combustion engine increases, but the risk of occurrence of knocking in a combustion chamber increases. Thus, according to the above embodiment (9), by appropriately controlling the ignition timing on the basis of the trade-off relationship between improvement of efficiency of the internal combustion engine and reduction of knocking occurrence frequency, it is possible to operate the internal combustion engine as efficiently as possible while avoiding damage to the internal combustion engine due to knocking as much as possible.
(10) In an embodiment according to the present invention, in the above method (9), the knocking occurrence frequency is calculated as a proportion of a combustion cycle in which occurrence of knocking is detected to total combustion cycles.
Further, according to the above method (10), the knocking occurrence frequency is calculated as a proportion of combustion cycles in which knocking occurrence is detected to total combustion cycles. Further, in the above method (10), a correlation between the knocking occurrence frequency obtained as described above and a change in the ignition timing is calculated, and the ignition timing of the internal combustion engine is controlled on the basis of the correlation. Thus, according to the above method (10), by detecting presence or absence of occurrence of knocking for a large number of combustion cycles and controlling the ignition timing on the basis of the detection result, it is possible to reduce the influence of variability of the knocking detection accuracy among combustion cycles. Further, according to the above method (10), by controlling the ignition timing on the basis of the knocking detection result obtained for a large number of combustion cycles, it is possible to reduce the influence of variability of sensibility of sensors used in the knocking detection part.
According to some embodiments of the present invention, the setting range of the time window corresponding to a knocking occurrence period and the setting range of the time window corresponding to a period without knocking are selected appropriately, and thereby it is possible to detect knocking with a higher accuracy.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly identified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not intended to limit the scope of the present invention.
For instance, an expression of an equal state such as “same” “equal” and “uniform” shall not be construed as indicating only the state in which the feature is strictly equal, but also includes a state in which there is a tolerance or a difference that can still achieve the same function. On the other hand, an expression such as “comprise”, “include”, “have”, “contain” and “constitute” are not intended to be exclusive of other components.
In the following description, before describing some embodiments according to the present invention, necessity of the ignition timing control taking account of knocking for an internal combustion engine, and the points that should be improved for the ignition timing control will be described in detail with reference to
As can be seen from comparison of the curves shown in
However, in many cases, a knocking detection result detected from the knocking severity contradicts with typical knocking characteristics that are actually observed. That is, with the knocking detection technique based on knocking severity, it may be difficult to detect occurrence of knocking accurately at a high accuracy. For instance, in some cases, when the phase of the ignition timing θig is set to become earlier gradually, the variation curve of knocking occurrence frequency based on knocking severity does not monotonically increases but tends to protrude upward with respect to the phase advancement of the ignition timing (i.e., tends to decrease after the local maximum point). Thus, in some embodiments according to the present invention, disclosed is a detection mechanism capable of detecting occurrence of knocking accurately at a higher accuracy than that of the knocking detection technique based on knocking severity, and an ignition timing control system including such a detection mechanism.
The gas engine 2 includes a cylinder 4, and a piston 6 connected mechanically to a crank shaft 10 via a crank 8. The space defined by the upper surface of the piston 6 and the capacity part of the cylinder 4 is the combustion chamber 12. A crank angle detector 42 is disposed on the crank shaft 10, and is configured to detect a phase angle of the crank shaft 10 and output a signal representing the current crank angle phase (crank angle phase signal) to the control device 100 described below. Furthermore, the crank shaft 10 is connected to a generator 44 configured such that a rotor rotates with rotation of the crank shaft 10. The generator 44 includes a torque sensor 46 that generates a detection signal of output torque of the crank shaft 10 from a current level and a voltage level of power generated. The torque sensor 46 outputs the generated detection signal of output torque to an output detection device 300 described below.
The cylinder 4 includes an air supply valve 18, an exhaust valve 22, and an ignition plug 30, on the upper surface of the combustion chamber 12. An air supply pipe 14 is connected to the air supply valve 18, and a mixer 24 for mixing air and fuel gas is connected to the air supply pipe 14. A fuel supply pipe 26 for supplying fuel gas to the mixer 24 and an intake pipe 16 for supplying air to the mixer 24 are connected to the mixer 24. A fuel adjustment valve 28 for adjusting the fuel supply amount to the mixer 24 is disposed on the connection portion between the mixer 24 and the fuel supply pipe 26. Furthermore, an exhaust pipe 20 is connected to the exhaust valve 22. Furthermore, the combustion chamber 12 formed by the upper surface of the piston 6 and the capacity part of the cylinder 4 may include a precombustion chamber 12a including an ignition plug disposed therein, and a main chamber 12b which is in communication with the precombustion chamber 12a via a nozzle hole 12c. In this case, on ignition of the precombustion chamber 12a, only a small amount of fuel gas for producing a torch exists in the precombustion chamber 12a, and is directly ignited by the ignition plug. Furthermore, the air-fuel mixture in the main chamber 12b being in communication with the precombustion chamber 12a via the nozzle hole 12c is ignited by a torch that jets out from the nozzle hole 12c in response to ignition of the precombustion chamber 12a.
Furthermore, the cylinder 4 includes an inner pressure measurement device 48 for measuring the inner pressure inside the combustion chamber 12. The inner pressure measurement device 48 measures a change in the inner pressure inside the combustion chamber 12, and outputs the change in the form of an inner pressure variation curve to a knocking detection part 110 described below. The cylinder 4 includes an inner pressure measurement device 48 for measuring the inner pressure inside the combustion chamber 12. The inner pressure measurement device 48 measures a change in the inner pressure inside the combustion chamber 12, and outputs the change in the form of an inner pressure variation curve. The cylinder 4 includes an acceleration sensor 49 which measures oscillation that occurs on the inner wall surface of the combustion chamber 12 due to pressure waves that occur upon combustion of air-fuel mixture in the combustion chamber 12 in the form of acceleration, and outputs the measurement value of the acceleration as an acceleration signal to a knocking detection part 110 described below.
Subsequently, with reference to
The control system 1 includes an air excess rate calculation device 200 for calculating an air excess rate of air-fuel mixture supplied to the combustion chamber 12, an output detection device 300 for detecting the output torque of the crank shaft 10, and a control device 100 for controlling the ignition timing of the gas engine 2. The air excess rate calculation device 200 receives the detection value of the supply amount of fuel and the measurement value of the precombustion chamber gas flow rate Qp from the fuel amount detector 210 connected to the fuel supply pipe 26. Further, the air excess rate calculation device 200 receives a caloric value of fuel gas and a detection value of the methane number MN from the fuel calorie detector 230 connected to the fuel supply pipe 26, and receives a detection value of the air amount from the air amount detector 220 connected to the air supply pipe 14. Furthermore, the air amount detector 220 includes a built-in thermometer (not shown) for measuring the intake temperature Ts, and outputs a measurement value of the intake temperature Ts to the air excess rate calculation device 200. Next, the air excess rate calculation device 200 calculates an air excess rate λ from the detection value of the supply amount of fuel gas, the detection value of the caloric value of fuel gas, and the detection value of the air amount, and outputs the air excess rate λ to the control device 100 together with the precombustion chamber gas flow rate Qp, the methane number MN, and the intake temperature Ts.
The output detection device 300 receives an electric signal (output torque signal) indicating the torque detection value of the crank shaft from the torque sensor 46, and outputs output torque detection value information representing the output torque of the crank shaft in watt to the control device 100. Furthermore, the inner pressure measurement device 48 and the acceleration sensor 49 provided for the cylinder 4 output a measurement value of the inner pressure inside the combustion chamber 12 and a measurement value obtained by measuring oscillation occurring on the inner wall surface of the combustion chamber 12 as acceleration to the control device 100.
The control device 100 includes a knocking detection part 110, a correlation update part 120, an optimum ignition timing calculation part 130, and an ignition timing control part 140. The knocking detection part 110 receives a crank angle phase signal representing the current crank angle phase θ from the crank angle detector 42, and receives the currently-set ignition timing θog from the ignition timing control part 140. Furthermore, the knocking detection part 110 receives the measurement value of the inner pressure variation inside the combustion chamber 12 and the measurement value obtained by measuring oscillation occurring on the inner wall surface of the combustion chamber 12 as acceleration, from the inner pressure measurement device 48 and the acceleration sensor 49.
Next, the knocking detection part 110 detects presence or absence of knocking occurrence every combustion cycle, for the currently-set ignition timing θig on the basis of the measurement value of the inner pressure variation and the measurement value of the acceleration variation received from the inner pressure measurement device 48 and the acceleration sensor 49. Further, the knocking detection part 110 outputs a knock-flag value Fknock to the correlation update part 120 as a knocking detection result of each combustion cycle. Herein, the knock-flag value Fknock is at 1 if the knocking detection part 110 detects occurrence of knocking in a combustion cycle, and is at 0 if knocking occurrence is not detected in a combustion cycle. The operation of the knocking detection part 110 to detect presence or absence of knocking occurrence every combustion cycle and output the knock-flag value Fknock every combustion cycle is performed repeatedly over a predetermined number CN of combustion cycles.
The correlation update part 120 receives CN knock-flag values Fknock outputted over CN combustion cycles from the knocking detection part 110, as a detection result of presence or absence of knocking occurrence. Next, the correlation update part 120 calculates a variation trend of a knocking occurrence frequency fk in the period from past to present, on the basis of the above CN knock-flag values Fknock and a series of knocking detection results previously received from the knocking detection part 110. Next, the correlation update part 120 updates the correlation between the change in the ignition timing θig and the change in the knocking occurrence frequency fk, on the basis of the current knocking occurrence frequency fk and the currently-set ignition timing θig. Further, the knocking occurrence frequency fk is calculated as a proportion of combustion cycles in which knocking occurrence is detected to total combustion cycles from past to present.
The optimum ignition timing calculation part 130 receives a latest content describing the correlation between a change in the ignition timing θig and the knocking occurrence frequency fk as correlation describing information, from the correlation update part 120. Furthermore, the optimum ignition timing calculation part 130 receives the precombustion chamber gas flow rate Qp, the methane number MN, the intake temperature Ts, the calculation value of the air excess rate λ, and the detection value of the output torque Pmi, from the air excess rate calculation device 200 and the output detection device 300. Next, the optimum ignition timing calculation part 130 determines the ignition timing θig of the gas engine 2 on the basis of the correlation between a change in the ignition timing θig and a change in the knocking occurrence frequency fk described by the correlation describing information.
In an illustrative embodiment, the optimum ignition timing calculation part 130 may determine an optimum ignition timing θig for the gas engine 2 as follows. First, the optimum ignition timing calculation part 130 estimates a variation trend of the thermal efficiency of the gas engine 2 corresponding to the change in the ignition timing θig, on the basis of the air excess rate λ, the output torque the precombustion chamber gas flow rate Qp, the intake temperature Ts, the methane number MN and the ignition timing θig received so far from the air excess rate calculation device 200 and the output detection device 300. Next, the optimum ignition timing calculation part 130 determines the optimum ignition timing θig taking account of the trade-off relationship between improvement of thermal efficiency of the gas engine 2 and reduction of the knocking occurrence frequency fk, on the basis of the above correlation between a change in the ignition timing θig and a change in the knocking occurrence frequency fk and the above variation trend of the thermal efficiency.
In another alternative embodiment, the optimum ignition timing calculation part 130 may receive only the variation trend of the knocking occurrence frequency fk from past to present from the correlation update part 120. In this case, the optimum ignition timing calculation part 130 may determine a new ignition timing θig for the gas engine 2 so as to retard the ignition timing θig from that of the present time, if the knocking occurrence frequency fk tends to increase at the present time. In contrast, the optimum ignition timing calculation part 130 may determine a new ignition timing θig for the gas engine 2 so as to make the ignition timing θig earlier than that of the present time, in a case where the knocking occurrence frequency fk tends to decrease at the present time.
Finally, the optimum ignition timing calculation part 130 outputs the newly determined ignition timing θig to the ignition timing control part 140. The ignition timing control part 140 controls the ignition timing θig of the gas engine 2 by using the ignition timing θig received from the optimum ignition timing calculation part 130 as a new control target value.
Subsequently, with reference to the flowchart of
Next, the process of the flowchart in
Next, the process of the flowchart in
In step S24 of the flowchart of
Next, the process of the flow chart in
Next, the process of the flowchart in
As described above, with the above control system 1 described with reference to
Next, with reference to
The oscillation waveform acquisition part 111 is electrically connected to the inner pressure measurement device 48 and the acceleration sensor 49 disposed on the cylinder 4 constituting the combustion chamber 12. The oscillation waveform acquisition part 111 receives a measurement value obtained by measuring variation of the inner pressure of the combustion chamber 12 from the inner pressure measurement device 48. Furthermore, the oscillation waveform acquisition part 111 receives a measurement value obtained by measuring oscillation that occurs as pressure waves due to combustion in the combustion chamber 12 act on the inner wall surface of the combustion chamber 12 as acceleration from the acceleration sensor 49. Furthermore, the oscillation waveform acquisition part 111 receives a crank angle phase signal outputted by the crank angle detector 42 to the knocking detection part 110 as a signal indicating the current crank angle phase B.
Next, the oscillation waveform acquisition part 111 receives oscillation waveform that occurs due to combustion of air-fuel mixture in the combustion chamber 12, on the basis of a measurement value of the inner pressure variation of the combustion chamber 12 received from the inner pressure measurement device 48 or a measurement value of acceleration variation received from the acceleration sensor 49. Herein, the oscillation waveform to be obtained by the oscillation waveform acquisition part 111 refers to a fine oscillation waveform observed on the inner wall surface of the combustion chamber 12 on occurrence of knocking, that is, high-frequency observed waveforms (order of kHz) including an oscillation frequency component that is unique to the time of occurrence of knocking. Acquisition of an oscillation waveform formed by combustion in the combustion chamber 12 by the oscillation waveform acquisition part 111 on the basis of the inner pressure variation in the combustion chamber 12 or the acceleration variation will be described below in detail with reference to
The time-frequency transform part 112 receives the oscillation waveform data from the oscillation waveform acquisition part 111, and then sets the first time window TW1 and the second time window TW2 on the time axis on which the above described oscillation waveform is obtained. On the time axis, the first time window TW1 is set at a point preceding the maximum inner-pressure time at which the inner pressure of the combustion chamber 12 is at its maximum in a single combustion cycle. On the time axis, the second time window TW2 is set at a point immediately after the maximum inner-pressure time. The time windows to be set on the time axis on which the oscillation waveform is observed will be described in below in detail with reference to
The knocking determination part 113 receives the above described first transform result R1 and the second transform result R2 from the time-frequency transform part 112, and sets the first frequency window FW1 and the second frequency window FW2 on the frequency axis in the frequency domain in which the first transform result R1 and the second transform result R2 are obtained. The frequency windows to be set on the frequency axis in the frequency domain in which the first transform result R1 and the second transform result R2 are obtained will be described in below in detail with reference to
In an illustrative embodiment, the first representative value P1 may include a first peak value at which the amplitude of the frequency domain expression of the first waveform portion WV1 is at its maximum in the first frequency window FW1. Similarly, in this embodiment, the second representative value P2 may include a second peak value at which the amplitude of the frequency domain expression of the second waveform portion WV2 is at its maximum in the second frequency window FW2. Then, in this embodiment, as a process of determining presence or absence of knocking occurrence on the basis of the relationship between the second representative value P2 and the first representative value P1, it may be determined whether knocking has occurred on the basis of the relationship between the second peak value and the first peak value.
According to this embodiment, when obtaining a representative value of the frequency domain expression, by using the peak value of a frequency spectrum curve corresponding to the frequency domain expression as a representative value, it is possible to obtain a representative value at a high speed through simple calculation. Thus, according to this embodiment, the process of determining whether knocking has occurred can be performed at a high speed with a low calculation load.
In another illustrative embodiment, the first representative value P1 may include a first partial overall (POA) value, which is a POA value calculated from the frequency domain expression of the first waveform portion WV1 in the first frequency window FW1. Similarly, in this embodiment, the second representative value P2 may include a second POA value which is a POA value calculated from the frequency domain expression of the second waveform portion WV2 in the second frequency window FW2. Then, as a process of determining presence or absence of knocking occurrence on the basis of the relationship between the second representative value P2 and the first representative value P1, it may be determined whether knocking has occurred on the basis of the relationship between the second POA value and the first POA value.
According to this embodiment, when obtaining a representative value of the frequency domain expression, a partial overall (POA) value of a frequency spectrum curve corresponding to the frequency domain expression is used as a representative value. A POA value is obtained by calculating the power spectrum of the frequency domain expression, calculating the power spectrum density on the basis of the calculated power spectrum, and calculating the square sum of the power spectrum density near the knocking frequency. Thus, when obtaining a representative value of the frequency domain expression, by using the POA calculated as described above as a representative value, it is possible to obtain a representative value taking account of all of the frequency components near the knocking frequency in the frequency domain expression. Thus, according to this embodiment, in the process of determining whether knocking has occurred, it is possible to use a representative value taking account of all of the frequency components near the knocking frequency in the frequency domain expression.
As a result of the above described series of processes performed by the oscillation waveform acquisition part 111, the time-frequency transform part 112, and the knocking determination part 113, presence or absence of knocking occurrence is detected for the current single combustion cycle. As a result, the knocking determination part 113 generates a knock-flag value Fknock indicating presence or absence of detection of knocking occurrence in the combustion cycle. Herein, provided that CN is a predetermined number of combustion cycles, the knocking determination part 113 determines whether CN knock-flag values Fknock are generated for respective CN combustion cycles. If only less-than-CN knock-flag values Fknock are generated for less-than-CN combustion cycles, the knocking determination part 113 returns the execution control to the oscillation waveform acquisition part 111. Next, the oscillation waveform acquisition part 111 obtains oscillation waveform that occurs due to combustion of air-fuel mixture in the combustion chamber 12 again to start the detection process of presence or absence of knocking occurrence for the next combustion cycle.
As a result of the above series or processing operations, if the knocking determination part 113 determines that CN knock-flag values Fknock are generated for the respective CN combustion cycles, the knocking determination part 113 outputs CN knock-flag values Fknock generated in the respective CN combustion cycles to the correlation update part 120.
Next, with reference to
In an embodiment, the oscillation waveform is extracted as a harmonic component from the inner pressure variation waveform in the combustion chamber 12 of the gas engine 2. The harmonic component is extracted as a component including an oscillation frequency component that is unique to the time of occurrence of knocking, from the inner pressure variation waveform. As a result, only by providing the inner pressure measurement device 48 having a simple configuration, such as an in-cylinder pressure sensor, in the cylinder 4 constituting the combustion chamber 12 of the gas engine 2, it is possible to obtain an oscillation waveform in the combustion chamber 12 necessary for detection of knocking, from the inner pressure variation waveform in the combustion chamber measured by the inner pressure measurement device 48. At this time, the oscillation waveform acquisition part 111 extracts an oscillation frequency component that is unique to the time of occurrence of knocking, from the measured inner pressure variation waveform. Accordingly, the oscillation waveform acquisition part 111 can extract, from the measured inner pressure variation waveform, only the frequency component excluding the basic frequency component that varies synchronously with the advancement of the combustion cycle (each stage of combustion cycle), as the oscillation frequency component unique to the time of occurrence of knocking.
In an alternative embodiment, the oscillation waveform is obtained as an acceleration detection waveform detected by the acceleration sensor 49 disposed on the cylinder 4 constituting the combustion chamber 12 in the gas engine 2. Thus, in this embodiment, only by providing the acceleration sensor 49 having a simple configuration for the cylinder 4 constituting the combustion chamber 12 of the gas engine 2, it is possible to directly obtain an oscillation waveform corresponding to the oscillation frequency component unique to the time of occurrence of knocking, from the acceleration variation waveform measured by the acceleration sensor 49.
Furthermore, in each of the two-dimensional graphs shown in
The waveform 71B shown in
Next, the process of the flowchart in
Specific examples of the first time window TW1 and the second time window TW2 set by the time-frequency transform part 112 are shown in
Hereinafter, specific examples of the first time window TW1 (81A in
That is, in
In the specific example shown in
In the example shown in
Next, the process of the flowchart in
In an embodiment shown in
Furthermore, in an embodiment shown in
Next, the time-frequency transform part 112 performs a time-frequency transform process of transforming the first waveform portion WV1 cut out from the oscillation waveform received from the oscillation waveform acquisition part 111 according to the first time window TW1 from a time-domain expression to a frequency-domain expression (step S53A). Furthermore, the time-frequency transform part 112 performs a time-frequency transform process of transforming the second waveform portion WV2 cut out from the oscillation waveform received from the oscillation waveform acquisition part 111 according to the second time window TW2 from a time-domain expression to a frequency-domain expression (step S53B).
In an illustrative embodiment, the transform of the first waveform portion WV1 or the second waveform portion WV2 from a time-domain expression to a frequency domain expression includes a process of transforming a time-series sample of the first waveform portion WV1 or the second waveform portion WV2 into a set including amplitudes of the respectively sampling frequencies, through a fast Fourier transform (FFT analysis). Thus, in this embodiment, it is possible to provide a plurality of (K) converters corresponding to a plurality of (K) sampling frequencies on the frequency axis, and to perform the calculation process of discrete Fourier transform on a plurality of time-series samples in parallel by using the plurality of (K) converters of parallel configuration. As a result, it is possible to perform fast transform of the first waveform portion WV1 or the second waveform portion WV2 to the frequency domain expression. Accordingly, even in a case where the rotation speed of the crank shaft is extremely high and it is necessary to detect occurrence of knocking in an extremely short period of time for each combustion cycle, it is possible to perform the frequency domain transform for the first waveform portion WV1 or the second waveform portion WV2 with a high speed in such detection.
Finally, the time-frequency transform part 112 outputs a first transform result R1 of transforming the first waveform portion WV1 in the first time window TW1 into a frequency domain expression through the time-frequency transform (e.g. FFT analysis), to the knocking determination part 113 (step S53A). Furthermore, the time-frequency transform part 112 outputs a second transform result R2 of transforming the second waveform portion WV2 in the second time window TW2 into a frequency domain expression through the time-frequency transform (e.g. FFT analysis), to the knocking determination part 113 (step S53B).
Next, the process of the flowchart in
Specific examples of the first frequency window FW1 and the second frequency window FW2 set by the knocking determination part 113 are shown in
Furthermore, specific examples of the first frequency window FW1 and the second frequency window FW2 set by the knocking determination part 113 are shown in
Next, the process of the flowchart in
Similarly, in step S55B, the knocking determination part 113 calculates the second representative value P2, which is a representative value of the frequency domain expression of the second waveform portion WV2 in the second frequency window FW2. For instance, according to an illustrative embodiment, in step S55B, the knocking determination part 113 may extract, as the second representative value P2, a second peak value P2 at which the amplitude of the frequency domain expression of the second waveform portion WV2 is at its maximum in the second frequency window FW2. Further, in another illustrative embodiment, in step S55B, the knocking determination part 113 may extract, as the second representative value P2, a second POA value P2, which is a POA value calculated from the frequency domain expression of the second waveform portion WV2 in the second frequency window FW2.
In the embodiment described below, to simplify the description, the first representative value P1 and the second representative value P2 are assumed to be calculated as the first peak value P1 and the second peak value P2 at which the amplitude of the above described frequency domain expression is at its maximum. Nevertheless, some embodiments described below can be implemented similarly even if the first representative value P1 and the second representative value P2 are calculated as the first POA value P1 and the second POA value P2 obtained as POA values from the frequency domain expression described above.
In an embodiment shown in
In an embodiment shown in
Next, the process of the flowchart in
In an illustrative embodiment, in step S56, the knocking determination part 113 divides the second peak value P2 by the first peak value P1 to obtain a peak ratio (P2/P1), and in step S57, performs the process of determining that knocking has occurred only if the peak ratio (P2/P1) is greater than a predetermined threshold. For instance, in step S56 shown in
Next, the process of the flowchart in
As a result of execution of the flowchart in
Accordingly, in the knocking detection method described above with reference to
In addition, in the above knocking detection method, the risk of occurrence of knocking is evaluated on the basis of two peak values P1 and P2 obtained from the frequency domain expressions of two respective waveform portions WV1 and WV2 included in the second time window TW2 and the first time window TW1, respectively, from the oscillation waveform generated by combustion of air-fuel mixture. As a result, with this knocking detection method, it is possible to evaluate the risk of occurrence of knocking while relatively comparing a peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period to a peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking. Therefore, according to the above knocking detection method, the setting range of the time window corresponding to a knocking occurrence period and the setting range of the time window corresponding to a period without knocking are selected appropriately on a reasonable basis, and thereby it is possible to detect knocking with a higher accuracy.
Furthermore, in an illustrative embodiment, the combustion chamber 12 includes a precombustion chamber 12a with a built-in ignition plug and a main chamber 12b in communication with the precombustion chamber 12a through a nozzle hole 12c. In this embodiment, the first time window TW1 may be set as follows. That is, the first time window TW1 may be set so as to include an ignition timing of the ignition plug inside the precombustion chamber 12a, in each combustion cycle of the gas engine 2. Herein, on ignition of the precombustion chamber 12a, only a small amount of fuel gas for producing a torch exists, and is directly ignited by the ignition plug. Thus, the risk of knocking due to abnormal combustion is extremely low. In addition, on ignition of the precombustion chamber 12a, it is possible to observe the oscillation waveform due to combustion of air-fuel mixture while knocking is not occurring. Accordingly, in this embodiment, it is possible to evaluate the risk of occurrence of knocking even more accurately, by comparing the peak values P1 and P2 of two frequency spectra obtained from two waveform portions included in the first time window TW1 including the ignition timing of the precombustion chamber 12a and the second time window TW2 corresponding to a knocking period, respectively.
Furthermore, in an illustrative embodiment, the first frequency window FW1 and the second frequency window FW2 may be selected so as to include a frequency component that appears as a peak frequency, from among frequency components of the impact wave generated in the combustion chamber 12 due to occurrence of knocking. As a result, the peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period and the peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking are extracted from a vicinity frequency range surrounding the peak frequency unique to the time of occurrence of knocking. Furthermore, the peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period and the peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking are extracted from a common peak vicinity frequency range. As a result, in this embodiment, it is possible to evaluate the risk of occurrence of knocking even more accurately, by relatively comparing a peak value of the frequency spectrum obtained from the oscillation waveform in a knocking occurrence period to a peak value of the frequency spectrum obtained from the oscillation waveform in a period without knocking.
Next, with reference to
The two curves 54C and 54D shown in
Furthermore, in the case shown in
The following can be understood from comparison of the variation curve (55C in
That is, the variation curve of knocking occurrence frequency obtained as a function of the ignition timing θig on the basis of knocking severity does not show a significant difference in the transition of the knocking occurrence rate even when the condition setting is changed considerably. In contrast, the variation curve of knocking occurrence frequency obtained as a function of the ignition timing θig according to an embodiment of the present invention shows a significant difference in the transition of the knocking occurrence rate by changing the condition setting.
Furthermore, the following can be understood from comparison of the variation curve (54C in
Furthermore, the following can be understood from comparison of the variation curve (54D in
As described above, by using the peak ratio calculated as a ratio of the first peak value P1 to the second peak value P2 according to an embodiment of the present invention as a knocking evaluation index, it is possible to detect occurrence of knocking with a higher accuracy than a typical knocking evaluation index. This is because, unlike the case in which knocking occurrence is detected on the basis of a typical knocking evaluation index, the knocking occurrence risk is evaluated on the peak ratio described as follows in an embodiment of the present invention. That is, according to an embodiment of the present invention, time-frequency transform (FFT analysis) is performed with two time windows provided in a time period of a single combustion cycle, and a peak ratio is obtained from two frequency spectra obtained therefrom. Furthermore, by evaluating presence or absence of knocking on the basis of a peak ratio according to an embodiment of the present invention, it is possible to evaluate a general trend of knocking with respect to the ignition timing. Furthermore, by evaluating presence or absence of knocking on the basis of a peak ratio according to an embodiment of the present invention, it is possible to detect a knocking occurrence trend which is substantially equal to the trend of non-continuous heat generation in the vicinity of the maximum inner pressure time in the combustion chamber 12 that can be observed at the time of occurrence of knocking.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2016-010723 | Jan 2016 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2016/088810 | 12/27/2016 | WO | 00 |
| Publishing Document | Publishing Date | Country | Kind |
|---|---|---|---|
| WO2017/126304 | 7/27/2017 | WO | A |
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| 2330284 | Jun 2011 | EP |
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| Number | Date | Country | |
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| 20200325835 A1 | Oct 2020 | US |
