DESC:TECHNICAL FIELD
[0001] The present subject matter relates to spark ignition engines. More particularly, detection of a misfire in a spark ignition engine using an ion current signal is disclosed.

BACKGROUND

[0002] Internal Combustion engines are significantly contributing to pollution and global warming by emitting various exhaust gases into the environment. An internal combustion engine produces power by burning of fossil fuel that emits harmful gases, such as, CO, HC, NOx and hydrocarbons. The emission of gases has been and is deteriorating the environmental condition and hence manufacturers are continuously stiving to improve design of engine to make them more greener and eco-friendly.
[0003] In addition to the control of emission of gases, the Automobile industry is implementing the “On board diagnostic (OBD)” on vehicles for intimating user about the status of vehicle conditions. OBD system is subdivided in two categories, viz. OBD I & OBD II. OBD II focuses on three main aspects – Engine misfire detection, Catalytic convertor monitoring, and Lambda sensor monitoring.
[0004] To improve engine combustion efficiency & reduce emissions, it is essential to detect and monitor misfire event in an internal combustion (IC) engine. Misfire occurs when the injected air fuel mixture does not burn at all or partially burns. Misfiring of the IC engine affects the quality of combustion and degrades the performance of a catalyst convertor, thereby leading to increase in emissions, which is undesirable.

BRIEF DESCRIPTION OF DRAWINGS
[0005] The detailed description is described with reference to the accompanying figures. The same numbers are used throughout the drawings to reference like features and components.
[0006] Fig. 1 exemplarily illustrates an ignition system with an ion current measurement circuit of an engine;
[0007] Fig. 2 exemplarily illustrates a controller unit electrically coupled to the ignition system exemplarily illustrated in Fig. 1;
[0008] Fig. 3 exemplarily illustrates a method of determining occurrence of misfire, measured by the controller unit, with respect to time;
[0009] Fig. 4 exemplarily illustrates a schematic diagram of determining occurrence of misfire, measured by the controller unit;
[00010] Fig. 5 exemplarily illustrate graphical representation of the ion current signal in misfire condition and no-misfire condition, in time domain;
[00011] Fig. 6a-6b exemplarily illustrates graphical representation determining the occurrence of misfire in the engine;
[00012] Figs.7a, 7b and7c exemplarily illustrates exemplarily illustrates a graphical representation comprising steps of determining the occurrence of misfire in the engine; and
[00013] Figs. 8a-8b exemplarily illustrates a graphical representation of a misfire flag signal generated by controller unit based on the determination of the peak of the sampled ion current signal.

DETAILED DESCRIPTION OF THE INVENTION
[00014] Misfire events in an Internal Combustion Engine can be categorized as partial or complete, based on the amount of combustion occurring during a particular engine cycle. In most engines, identification of misfire is performed by monitoring angular acceleration of engine crank-shaft. However, single cylinder engines with lower capacity (example less than 200 cubic centimeter) provide challenges to identify misfire due to low mechanical inertia of the IC engine using the above specified approach. The problem of misfire identification for the single cylinder IC engines turns out to be more challenging due to presence of various load disturbances on the power train, when the engine is employed in a vehicle.
[00015] Several other techniques are designed for the detection of engine misfire for the single cylinder engines. Such techniques include analysis of instantaneous crankshaft speed, analysis of in-cylinder pressure, analysis of instantaneous crankshaft torque, etc. Evaluation of the crankshaft speed for detection of misfire faces a lot of challenges due to low mechanical inertial and load disturbances in engines. Alternate solutions to address the problem of detection of misfire event in the engine utilize the ion current generated in a sparking event in the engine. When air-fuel mixture ignites inside the IC engine cylinder, air particles get ionized. By applying a suitable high-voltage on a spark plug, it is possible to measure the ion current as the amount of ion current reflects the level of ionization of the air-fuel mixture. Thus, the flow of ion current signal depends on the combustion event. The ion current signal can be captured with the help of an ion current measurement circuit. The captured signal needs to be processed to detect misfire. Multiple techniques can be applied to differentiate the misfire from normal combustion with the help of the ion current signal.
[00016] Calculus Integral of the ion current signal is a common technique to detect misfire. However, the integral of ion current signal shows error for partial misfire as the value of integral coincides for misfire and No-misfire condition. There are various reasons which can result in engine misfires. Electrical failure in the ignition coil circuit is one of them. No flow of ion current in the ignition coil helps detects complete misfire. However, in cases where a feeble spark is generated across the spark plug, it results in partial misfire. In such scenario, the detection of misfire using the ion current signal demands for filtering and processing the ion current signal to extract the information which is cumbersome and likely to be inaccurate.
[00017] Ion current signal shows lot of dynamics in ‘No Misfire’ condition compared to that of misfire condition. Frequency spectrum of the signal can be used to extract the essential information and to differentiate between ‘No Misfire’ and ‘Misfire’ condition. Fast Fourier Transform (FFT) is performed to observe the features of signal in frequency domain. The misfire will be detected by extracting the information about the trend and shape of FFT of ion current signal in every spark event instead of magnitude with respect to engine cycle. However, the disadvantages of detecting misfire through FFT method is that it requires large set-up (typically offline determination) requiring Field Programmable Gate Array (FPGA) and complex frequency conversion units to convert time domain signal into frequency domain signals. Further, a large number of samples to be stored requiring large space of memory which delays processing of the ion current signal till determination of misfire. Hence, the vehicle indication of occurrence of misfire may not be feasible by using the above mentioned methods as it requires data to be collected online and processed offline.
[00018] In vehicles with combustion engine, following are the disadvantages of misfire condition: Due to the presence of misfire in combustion event, fuel will be wasted as there is no spark for fuel to burn. This will degrade the performance of vehicle leading to reduction in mileage. Misfire detection will intimate driver about the misfire events in the vehicle and by investigating and rectifying the causes of misfire, the user can improve the performance of vehicle. Detection and rectification of misfire will have an adverse impact on the durability of vehicle. Further, misfire has direct impact on power/pick up of vehicle as there is loss of combustion event. The user may feel a sudden jerk in driving due to misfire. These may cause discomfort to driver. Also, due to misfire, the unburnt fuel in the exhaust affects the life of the catalyst in the converter and has adverse impact on emissions. Therefore, there exists a need for detecting no-misfires, complete misfires, and partial misfires effectively based on ion current sensing for smooth experience, enhanced durability, and adherence to emission targets by the engine.
[00019] The present subject matter discloses a new method of utilizing magnitude of voltage level in ion current signal and shape of ion current signal, generated during a sparking event in an engine, for information about a misfire event (complete or partial) in the engine. Thus, the ion current measurement is indicative of the combustion event as well as the quality of combustion in the engine. The ion current signal displays dynamics in a no-misfire condition compared to that of a misfire condition. Peak detection of the ion current signal is used to extract the essential information and to differentiate between the no-misfire condition and misfire condition in the engine.
[00020] Peak detection method is herewith employed for misfire identification. Ion current signal shows lot of dynamics in ‘No Misfire’ condition compared to that of ‘Misfire’ condition. The flow of ion current signal depends on the combustion event. The ignition of air fuel charge results in spark current flowing through the coil. The high voltage spark ionizes the air molecules in the spark plug air gap. The ions produced can be measured in the form of ion current by applying a voltage across the spark plug electrodes. The ion current is directly proportional to the amount of ions produced during the combustion event. A measurable amount of ion current with sudden spike in ion current signal is observed during ‘No misfire’ condition due to presence of ions. However, any spike is absent during ‘misfire’ condition. The amount of ion current signal is very small during misfire. Peak detection method is used to identify misfire since the peak of ion current during ‘No Misfire’ condition is considerably greater compared to that during ‘Misfire’ condition. A threshold value is set for different engine speed and load. The threshold value is so defined such that the peak of ion current will always be greater than threshold during normal operating condition and it is less during misfire condition.
[00021] In an embodiment, a misfire controller unit of an engine is disclosed that comprises an ion current measurement circuit, a sampling unit and a peak detection unit. The ion current measurement circuit measures an ion current signal in an ignition coil generated during a spark event in a spark plug. The strength of ion current varies with the amount of ions present in it. In case of a normal combustion i.e. a ‘No Misfire’ condition, the strength of ion current is more as compared to a ‘Misfire’ condition. In an embodiment, the controller unit comprises of a signal conditioning unit which is provided for filtering and modification of the ion current signal. The ion current signal measured with ion current measuring circuit typically varies from 0V to 20V and the sampling unit is configured to accept the values from 0V to 10V. Hence, the signal conditioning unit is configured to match the output of Ion current measurement circuit to the input of the sampling unit. Also, a protection circuit is provided so that the input at the misfire controller unit will never be allowed to go above its maximum rating. Further, the sampling unit is provided with either an external analog to digital convertor or an in-built analog to digital convertor to convert ion current signal from an analog signal to a digital signal. A low-pass filter is also provided to filter out the noise in the ion current signal and to modify the signal as per the requirements of sampling unit. As per alternative embodiments, the low-pass filter may be inside or outside the signal conditioning unit. The controller unit is configured with a peak detection unit to analyze a peak or a spike generated in a ‘No Misfire’ condition, said peak being greater than a pre-determined threshold value of ion current signals for a normal combustion event. However, there will be no peak or a spike during ‘Misfire’ condition. Hence, the peak detection unit as per present invention accurately and instantaneously determines occurrence of a misfire in the engine.
[00022] Further, the above-mentioned pre-determined threshold of ion current signal is fetched by the peak detection unit, where the threshold value is being prestored in the memory of controller unit for various range of engine speeds and loads. Generally, the peak value of the ion current changes depending on the operation state of the engine; when the engine speed is low, the peak value tends to become small and when the engine speed is high, the peak value tends to become large. The threshold value is also based on the variations of primary input voltage in the ignition coil. Hence, a look-up table is created and prestored in the memory of the controller unit based on parameters like engine speed, load, primary input voltage in ignition coil. There will be a different threshold value for every different sample within a spark event.
[00023] The present invention focusses on detection of peak by comparing peak value in ‘No misfire’ and ‘Misfire’ condition with the set threshold. Amplitude and shape of Ion current signal in ‘Misfire’ condition is different than during ‘No Misfire’ condition. When a user switches on the ignition switch, an ignition coil signal is generated and same is designated as a trigger signal. The trigger signal denotes that sparking has occurred in the engine. A digital port of the misfire controller unit is configured to take the trigger signal as an input. Based on the trigger signal, an ion current signal is recorded in memory of the misfire controller unit. The ion current signal passes through the signal conditioning unit provided with a low-pass filter to filter and refine the ion current signal. The filtered and modified ion current signal then passes through the sampling unit comprising an analog to digital convertor which is communicatively coupled with the signal conditioning unit. Further, the analog to digital convertor then converts the filtered and refined ion current signal into N number of sampl signalswhere N is a desired number of sample signals determined by the manufacturer. The filtered and refined ion current signal is divided into N samples based on predefined sampling frequency determined by the manufacturer and the samples are collected within a time duration based on the sampling frequency. For e.g. the samples of ion current signals being collected at every 0.02 miliseconds is being sampled at 50 kHz. Hence, the sampling of the ion current signal is done at a pre-determined frequency and the samples are collected in a specified sampling time and stored within the controller unit. An amplitude of voltage level of sampled ion current signal generated through one spark event is compared with pre-determined threshold value fetched by peak detection unit from the look up table of the misfire controller unit. The pre-determined threshold value can be set depending on engine rpm and load. The pre-determined threshold value defined by the manufacturer can vary w.r.t. engine speed, hence the look up table is being referred by the misfire controller unit with varying engine speed. If the value is above the set threshold, it gives signal of ‘No misfire’ event and if it is below the set threshold, it gives signal of ‘Misfire’ event.
[00024] Further, each sample generated within a pre-determined sampling time in a spark event is compared with pre-determined threshold value of ion current signal. A numeric counter is provided externally or in-built in the controller unit. The counter will increment the count of the samples till it reaches the pre-determined number of samples. Once the counter reaches the pre-determined number of samples, a peak detection unit will detect if the peak or spike has occurred in the pre-determined number of samples. If the peak or spike is detected, then it will be flagged as a ‘No Misfire’ condition or else it will be flagged as a ‘Misfire’ condition. In an embodiment, the controller unit may set a misfire flag and a no-misfire flag based on the analysis. Further, a ‘Misfire’ condition will be indicated to the user through a malfunction indicator lamp or any other method of notification present in the vehicle or user device.
[00025] The present invention seeks for synchronous measurement in which ion current signal will be captured after taking reference from ignition coil signal and the ion current signal in particular region only will be captured and used for misfire detection. Hence, to detect a peak or spike in the ion current signal, the controller unit need not record an entire waveform to detect a peak. This method has a significant advantage over the prior arts using integral of ion current signal and FFT to determine the misfire where it needs to collect sample points for entire cycle and then process the data. However, the peak detection method uses very few samples and there is no excess processing time. Misfire will be detected in the same engine cycle or within a spark event.
[00026] In an embodiment, the vehicle comprises of a notification unit for generating and notifying a user of the engine on occurrence of the misfire, based on misfire flag generated by peak detection unit. The peak detection unit is provided to distinguish the peak of ion current signal under a ‘misfire’ condition and a ‘no-misfire’ condition. Further, according to one embodiment, the misfire controller unit may be a part of electronic control unit (ECU) which may be provided in a vehicle.
[00027] In another embodiment, a method for determining a misfire in an internal combustion engine is disclosed. The method is implemented by the misfire controller unit disclosed above. The method comprises the steps of: measuring voltage levels of an ion current signal received from an ignition coil of the IC engine, during a sparking event in a spark plug, by an ion current measurement circuit; filtering and refinement of the received ion current signal by a low pass filter. Said low pass filter may or may not be provided in a signal conditioning unit. Said low pass filter will filter out any noise from the ion current signal to give a smooth noise free signal; further refinement of an ion current signal is carried out by the signal conditioning unit to generate values of the ion current signal between a desired range of voltage; sampling of the ion current signal by a sampling unit into a predetermined number of samples; and analyzing a peak in predetermined number of samples of the ion current signals by the peak detection unit to determine occurrence of a misfire in an engine.
[00028] Further, the method implemented by a peak detection unit comprising the steps of: comparing magnitude of a voltage level of a plurality of samples in the sampled ion current signal with a pre-determined threshold voltage; determining the occurrence of the no-misfire and an occurrence of a normal combustion in the engine, when magnitude of the voltage level of at least one sample is one of greater than or equal to the pre-determined threshold voltage; and determining the occurrence of the misfire in the engine, when the magnitude of the voltage level of at least one sample is not greater than the pre-determined threshold voltage.
[00029] In an embodiment, analyzing an amplitude of each of the predetermined number of samples of ion current signals by the peak detection unit comprises: performing a lookup for each sample of ion current signal and a corresponding pre-determined threshold signal is generated based on engine rpm; detecting a peak being generated above set threshold signal; and determining the occurrence of the misfire in the engine where detection of peak corresponds to ‘No misfire’ or normal combustion condition and no peak detection being flagged as a ‘Misfire’ condition.
[00030] Fig. 1 exemplarily illustrates an ignition system (100) along with an ion current measurement circuit (107) of an engine. The ignition system (100) consists of an ignition coil with a primary side (101) and secondary side (103), a spark plug (106), and a control circuit (105), for example, an electronic control unit (ECU) with an electrical switching device (104) to produce a high voltage spike required to generate a spark in a cylinder of the engine (not shown). The primary coil (101) is connected between a battery (102) and the electrical switching device (104). When the electrical switching device (104) is in a closed state, the primary side (101) of the ignition coil stores energy. As soon as the control circuit (105) changes the state of the electrical switching device (104) to open state, a voltage e.g. 400V is generated on the primary side (101) of the ignition coil due to the sudden interruption of current flow in the inductive circuit. A secondary high voltage of around 20-25 kV (depending upon the turn ratio of primary & secondary coils) is generated at the spark plug (106), which results into voltage breakdown and thus allows the flow of ion current. The ion current measurement circuit (107) is connected at the secondary side (103) to provide a biasing voltage which in turn generates the flow of ion current. The ion current measurement circuit (107) consists of a capacitor which is charged during trigger of the spark. Once the spark is triggered, the charge held by the capacitor generates a potential difference across the spark electrodes, which results in flow of the ion current. The ion current measurement circuit (107) is connected to a terminal (103B) of the secondary side (103) of the ignition coil (101 and 103) to detect misfire. The captured ion current signal needs to be filtered and processed to extract the essential information pertaining to combustion event in the engine (not shown).
[00031] Fig. 2 exemplarily illustrates a controller unit (200) electrically coupled to the ignition system (100) exemplarily illustrated in Fig. 1. The controller unit (200) comprises the ion current measurement circuit (107) connected to the secondary side (103) of the ignition coil. The controller unit (200) comprises a signal conditioning unit (203), a sampling unit (205) and a peak detection unit (204) that is electrically coupled with the ion current measurement circuit (107).
[00032] The ion current measurement circuit (107) measures the ion current signal flowing through the secondary side (103) of the ignition coil. The ion current measurement circuit (107) measures the voltage level of the ion current signal. The variation in the amplitude of voltage levels of the ion current signal during a misfire event and a no-misfire event is shown in Fig. 5.
[00033] The trigger signals from engine speed, ignition coil and spark plug are taken as inputs for signal conditioning unit (203). Predetermined engine speeds are used to trigger the start and end of the detection of the misfire by the misfire detection system (200). Further, ion current measurement circuit (107) sends ion current signal based on the spark event and ionization of air-fuel mixture by a spark plug electrode of the spark plug (106). The ion currents signal filtering and refinement of received ion current signal is carried out by the signal conditioning unit (203). The low pass filter (202) being provided in the signal conditioning unit (203) is used to attenuate the noise and to refine the signal and thereby obtain an improved signal. A misfire controller unit (200’) comprises of an analog to digital convertor unit (205), a peak detection unit (204) and a signal conditioning unit (203). Said analog to digital converter unit (205) being configured for converting the filter and refined ion current signal into N number of samples where N are desired number of samples determined by the manufacturer. The filtered and refined ion current signal is divided into N samples based on sampling frequency and the samples are collected within a time duration based on a predetermined sampling frequency. For e.g. the samples of ion current signals being collected at every 0.02 miliseconds is being sampled at 50 kHz. Hence, the sampling of the ion current signal is done at a pre-determined frequency and the samples are collected in a specified sampling time and stored within the controller unit (200’). An amplitude of voltage level of sampled ion current signal generated through one spark event is compared with pre-determined threshold fetched by the peak detection unit (204) from a look up table defined in the misfire controller unit (200’). The pre-determined threshold value in the controller unit (200’) is set by the manufacturer for an range of engine rpm and load. The pre-determined threshold value set by manufacturer varies w.r.t. engine speed, hence the look up table is being referred by the peak detection unit (204). If the value of detected filtered and refined signal is above the set threshold, it is flagged as ‘No misfire’ event in the misfire controller unit (200’) and if it is below the set threshold, it is flagged as ‘Misfire’ event. The vehicle comprises a notification unit (207) for generating and notifying a user of the engine on occurrence of the misfire, based on the analysis by the misfire controller unit (206). Based on the misfire flag and the no-misfire flag, the notification unit (207) sends a notification to a user device of the user. The user device may be a smart phone, a desktop, a laptop, an instrument cluster of the vehicle, etc. The notification may be a voice alert, a text notification communicating an error code and the related information on the identified fault to the user. The notification may later on be used for diagnosis and rectification of the fault by a service engineer. The detection of the misfire as per the present invention, is performed in real-time continuously, since no data is stored for later processing.
[00034] Fig. 3 exemplarily illustrates a method of determining occurrence of misfire, measured by the controller unit (200’), with respect to time. As can be seen, the voltage levels of the ion current signal exhibits dynamics at the initiation of the misfire condition and the no-misfire condition. The variation in the voltage levels are analyzed by other components of the controller unit (200’) discussed in detailed description of Fig. 2 to determine occurrence of the misfire. The method followed by the controller unit (200’) comprises the steps of: The ion current measurement circuit (107) measures an ion current signal in an ignition coil generated during a spark event in a spark plug (106) (step 301), further the ion current signal is sent to the signal conditioning unit (203) which further comprises of a low pass filter (202) that filters the noise from the received ion current signal. Further, the sampling of filtered & refined ion current signal is done by the sampling unit (205) (Step 302). After sampling of the filtered and refined ion current signal, the peak detection unit (204) determines an occurrence of one of a misfire and a no-misfire in the engine, based on detection of at least one peak in sampled ion current signal (step 303).
[00035] Fig. 4 exemplarily illustrates the flow chart of method for detection of misfire in the engine. At step 401, as soon as the engine starts and has achieved a predetermined engine rpm and the ignition circuit is initiated by the user, the ignition coil is energized and sparking occurs with the help of spark plug (106) which ionizes the air-fuel mixture to cause normal combustion of the fuel. This sends a trigger signal to the controller unit (200’) and the processing of the ion current signal determined by the ion current measurement circuit (107) is initiated. When a trigger signal is generated then the predetermined threshold for the ion current signal, depending on the engine rpm, is fetched (Step 403, Step 404). If the trigger signal is not generated, all the parameters such as trigger input, engine rpm condition, counter for analog samples, ion current signal, analog input and the threshold value to be set to the default values (Step 403). Sampling of the signals are done by the sampling unit (205) and corresponding pre-determined threshold value is fetched. Controller unit (200’) sets a counter and increments the counting of the samples till it reaches the predetermined N samples (Step 405). The sampled ion current input is compared with the pre-determined threshold value of ion current signal corresponding to respective engine rpm and load (Step 406). If the sampled ion current input is greater than the pre-determined threshold value then count for peak detection increments else there will be no change in the peak detection count (Step 407 and Step 408). At Step 409, when number of samples is less than the predetermined number for ion current samples i.e. N number of sample for e. g. 100 samples are determined for an ion current signal and if the count is less than 100, the counter will keep on incrementing till it reached the 100th sample and steps 405 to steps 409 will be repeated. Once, all the 100 or N samples are collected, misfire condition by the peak detection unit (204) is determined (Step 410). If any peak or spike is detected and the voltage level of the peak/ spike is above the pre-determined threshold voltage then ‘No-Misfire’ condition is determined, else ‘Misfire’ condition is determined and based on the misfire flag, the notification unit (207) generates a notification to notify the occurrence of the misfire to the user of the engine (Step 411).
[00036] Figs. 5 exemplarily illustrate graphical representations of the ion current signal in misfire condition and no-misfire condition, in time domain. As exemplarily illustrated in Fig. 4, the ion current signal in time domain is obtained by ion current measurement circuit (107). The graphical representation shows variation in the amplitudes of the ion current signal during misfire condition and no-misfire condition. The samples of filtered and modified ion current signal are captured at a predetermined time interval. The time intervals are determined on sampling frequency that can be determined by the manufacturer. In the figure 5, the time vary from T1, T2, T3,…TN where T1, T2…TN is determined through sampling frequency. N are the number of pre-determined samples and TN is the time for Nth sample. Further, the amplitude of the ion current signal varies from V1, V2, …, to V6 where V1 to V6 are the amplitude of the voltage output of the ion current signal. From the graph, it is illustrated that the magnitude of voltage level of ion current signal during a ‘Misfire’ condition is less than the magnitude of voltage level of ion current signal during a ‘No Misfire’ condition.
[00037] Fig. 6a and Fig. 6b exemplarily illustrates a graphical representation determining the occurrence of misfire in the engine. In fig 6a represented in time domain, the primary voltage varies based on engine rpm and accordingly the pre-determined threshold value for ion current signal also varies. The ion current signal flows in the negative direction and hence negative values for ion current signal are received. However, the magnitude in the voltage level of the ion current signal is compared with the pre-determined threshold value and as can be seen from the graph the magnitude of the ‘no-misfire’ condition is greater than ‘misfire’ condition and hence, there is a clear difference between the misfire condition and the normal combustion of the air-fuel mixture. There is a peak/spike captured in a pre-determined time duration during a normal combustion. The time duration is based on sampling frequency and since only a small part of ion current signal is captured and not the entire waveform, such accurate and short time duration is achieved through the experimental data received from several tuning and calibration iterations gathered after performing the misfire detection through controller unit (200’). In the graph, the area inside the signal captures the misfire condition and there is no peak or spike detected in such area, rather the value of ion current signal is below the pre-determined threshold value and the value is reaching towards zero in case of complete misfire condition. In Figure 6b represented in frequency domain, according to one embodiment, it is shown that a trigger signal is generated when the ignition coil is energized and sparking occurs through spark plug, the digital input of such trigger signal goes to the controller unit (200’). In case of misfire as indicated by the trough region, there will be no peak detected and the digital output will be ‘0’. In case of normal combustion, the digital output is ‘1’.
[00038] Fig. 7a represented in frequency domain, exemplarily illustrates a graphical representation comprising steps of determining the occurrence of misfire in the engine. The peak detection signal is the digital output of the voltage values of received ion current signal detecting a peak or the spike above a pre-determined threshold value of ion current signal. In case of misfire, there will be no peak detected and the digital output will be ‘0’. In case of normal combustion, the digital output is ‘1’. Based on the peak detection signal, a misfire flag is generated as shown in Fig. 7b, whenever the misfire is detected, the digital output value of the misfire flag is ‘1’ indicating the ‘Misfire’ condition and a ‘0’ value indicating the ‘No Misfire’ condition. Fig. 7c shows the graphical representation of the ion current signal output based on which a peak detection signal and misfire flag is generated.
[00039] Fig 8a and 8b represented in time domain, exemplarily illustrates a graphical representation of a misfire flag signal generated by controller unit (200’) based on the determination of the peak of the sampled ion current signal and sends the misfire flag to the notification unit (207) thereby indicating the occurrence of misfire to the user.
[00040] The present invention provides the following technological advancements in the field of on-board diagnostics of IC engines as follows: the present invention discloses a new method and circuit to accurately & instantaneously detect a misfire and a partial misfire in a spark ignition engine by analyzing ion current signal in time domain with the help of peak detection techniques. Essential information is extracted in time domain by comparing ion current signal during ‘Misfire’ and ‘No Misfire’ condition and appropriate threshold conditions are preset to differentiate misfire from normal combustion. The current subject matter enables overcoming the drawbacks of the known art and ensures the misfire is accurately detected thereby enabling reliable control and reduction of emissions for an engine especially of a small capacity.
[00041] Also, the sparking event is very fast phenomenon with a maximum time of few milliseconds. Ion current signal flows through the circuit rapidly the moment spark ends. Hence, in order to collect large set of data pertaining to the sparking event in a short duration, the sampling unit with very high sampling rate are implemented in the present invention. The low pass filter and signal conditioning unit, filters out the ion current signal within defined frequency band so that the digital ion current signals of respective frequency bands can be compared accurately. Also, the frequency bands are intelligently chosen such that the digital ion current signal shows significant variations in both ‘Misfire’ and ‘No Misfire’ condition. The engine speed and the voltage on the primary side of the ignition coil are both used as reference to determine the misfire by the controller unit. The signals from engine speed and voltage of primary side of ignition coil are used to improve the reliability of the controller unit. If incase voltage of primary side of the ignition coil is not detected due to some fault, engine speed will act as a reference for the misfire detection in real time.
[00042] Misfire detection based on ion current measurement will intimate user of the engine about the misfire events in the spark ignition engine of a vehicle in real time and by investigating and rectifying the causes of misfire, the performance of the vehicle is improved, thereby improving reliability, durability, mileage of the vehicle, and comfort offered to the user of the vehicle. Also, the vehicle enables achieving OBD II targets. Also, timely detection of misfire in the engine and rectification of the fault reduces degradation of the catalyst and enhances the performance by achieving target lambda value in the engine of the vehicle.
[00043] In addition to detecting the occurrence of the misfire, the controller unit can also be configured with a peak detection unit which can perform determination of state of engine where the state can be one or more of a knock detection, spark plug timing determination and spark duration measurement which enable performing analysis of quality of combustion in the engine, and aid in spark plug maintenance of the engine, using ion current sensing technology. Another aspect of present invention is to analyse the quality of combustion in the engine by determining ion current signal.
[00044] Other aspect of present invention is to provide ease in maintaining spark plug provided to ignite the air/fuel mixture. If there are occurrence of multiple ‘Misfire’ conditions in the engine, servicing and maintenance of spark plug may minimize said occurrences.
[00045] Yet another aspect of present invention is reliable knocking detection for less consumption of air-fuel mixture and more torque. “Knocking” occurs when the air-fuel mixture self-ignites prematurely and hence the determination of peak of ion current signal with the help of controller unit may help in detection of knocking in the engine.
[00046] Another aspect of the present invention is monitoring the lambda value of the vehicle through controller unit based on detection of peak of ion current signal. Lambda is the ratio between the amount of oxygen actually present in a combustion chamber versus the amount that should have been present to get perfect combustion. Hence, analysis of lambda may be done through controller unit.
[00047] Improvements and modifications may be incorporated herein without deviating from the scope of the invention.
LIST OF REFERENCE NUMERALS
In Figure- 1
100- Ignition system
101-primary side of ignition coil
102- battery positive terminal
103- secondary side of ignition coil
104-control unit
105-switching device
106- spark plug
107- ion current measurement circuit

In Figure-2,
200- Misfire Detection System
200’-Misfire Controller Unit
201- Engine speed input
202-Low pass filter
203-Signal conditioning unit
204-Peak detection unit
205-ADC, Sampling unit
207-Notification unit

In Figure-3,
301-303- Steps to detect misfire by misfire detection system

In Figure-4,
401-412- Steps shown to determine a method for detection of misfire in the engine
,CLAIMS:We Claim:
1. A controller unit (200’) of an engine, said controller unit (200’) comprising:
an ion current measurement circuit (107) for measuring an ion current signal in an ignition coil (101 and 103) generated during a spark event in a spark plug (106), wherein said ignition coil (101 and 103) including a primary side of ignition coil (101) and a secondary side of ignition coil (103),
a sampling unit (205) being configured for sampling said ion current signal, and
a peak detection unit (204) determining an occurrence of one or more state of said engine,
wherein said one or more state of said engine being a misfire and a no-misfire in said engine, a knocking state of said engine, spark plug timing of said engine, spark duration of said engine, lambda value of said engine
wherein determination of said one or more state of said engine being based on detection of at least one peak in said sampled ion current signal.

2. The controller unit (200’) as claimed in claim 1, said controller unit (200’) being configured with a method for determining occurrence of one of a misfire and a no misfire in said engine, said method comprising steps of
comparing by said peak detection unit (204), magnitude of a voltage of a plurality of samples in said sampled ion current signal with a pre-determined threshold voltage,
determining by said peak detection unit (204), one of said occurrence of said no-misfire in said engine when magnitude of said voltage level of at least one sample is one of greater than or equal to said pre-determined threshold voltage, and
determining said occurrence of said misfire in said engine when the magnitude of said voltage level of at least one sample is not greater than said pre-determined threshold voltage.

3. The controller unit (200’) as claimed in claim 2, wherein the said peak detection unit (204) sets one of a misfire flag on determining said occurrence of said misfire and a no-misfire flag on determining said occurrence of said no-misfire.

4. The controller unit (200’) as claimed in claim 1, wherein said controller unit (200’) comprises of a signal conditioning unit (203) for receiving said ion current signal, filtering out noise from said ion current signal and refining said ion current signal to provide a filtered and refined ion current signal.

5. The controller unit (200’) as claimed in claim 4, wherein said signal conditioning unit (203) comprising a low pass filter (202) to filter out noise.

6. The controller unit (200’) as claimed in claim 5, wherein said controller unit (200’) comprises of an analog to digital converter (205), wherein said analog to digital converter (205) being provided within said sampling unit (205), said analog to digital converter (205) being configured with a high sampling rate for reading and converting said filtered and refined ion current signal to said sampled ion current signal, said samples ion current signal being fed to said peak detection unit (204) for processing said sampled ion current signal.

7. The controller unit (200’) as claimed in claim 2, wherein a predetermined threshold for said sampled ion current signal being fetched by said peak detection unit (206) from a look up table, said lookup table being configured based on an engine rpm and engine load, said look up table being prestored inside memory of said controller unit (200’).

8. The controller unit (200’) as claimed in claim 2, wherein a predetermined threshold for said sampled ion current signal being fetched by said peak detection unit (206) from a look up table, said lookup table being configured based on one or more of an engine rpm and voltage on primary side of ignition coil (101), said look up table being prestored inside memory of said controller unit (200’).

9. The controller unit (200’) as claimed in claim 3, wherein said engine being provided in a vehicle, said vehicle being provided with a notification unit (207), said occurrence of said misfire being indicated by said notification unit (207), based on said misfire flag.

10. A method for determining occurrence of a misfire or a no misfire in an engine, said method being implemented by a controller unit (200’), said engine being configured with an ignition coil (101 and 103), a spark plug (106), said controller unit (200’) including an ion current measurement circuit (107), a sampling unit (205), and a peak detection unit (204),said method comprising the steps of:
measuring an ion current signal in said ignition coil (101 and 103) generated during a spark event in said spark plug (106) by said ion current measurement circuit (107),
sampling said ion current signal by said sampling unit (205), and
determining an occurrence of one of a misfire and a no-misfire in said engine, said detection being based on detection of at least one peak in said sampled ion current signal by said peak detection unit (204).

11. The method as claimed in claim 9, wherein the method implemented by said peak detection unit (204) comprising the steps of:
comparing magnitude of a voltage of a plurality of samples in said sampled ion current signal with a pre-determined threshold voltage,
determining said occurrence of said no-misfire and an occurrence of a normal combustion in said engine, when magnitude of said voltage level of at least one sample is one of greater than or equal to said pre-determined threshold voltage, and
determining said occurrence of said misfire in said engine, when said magnitude of said voltage level of at least one sample is not greater than said pre-determined threshold voltage.

12. The method as claimed in claim 10, wherein said controller unit (200’) being configured to set one of a misfire flag on determination of said occurrence of said misfire and a no-misfire flag on determination of said occurrence of said no-misfire, said determination being by said peak controller unit (204).

13. The method as claimed in claim 9, wherein generation of filtered and refined ion current signal by a signal conditioning unit (203), said signal conditioning unit (203) being communicatively coupled with said sampling unit (205).

14. The method as claimed in claim 12, wherein filtering out noise from said ion current signal and refinement of said ion current signal being achieved by a low pass filter (202) of said signal conditioning unit (203).

15. The method as claimed in claim 12, wherein conversion of said filtered and refined ion current signal to said sampled ion current signal is being done by an analog to digital converter (205), wherein said analog to digital converter (205) being capable of a high sampling rate, said analog to digital converter (205) being provided within said sampling unit (205).

16. The method as claimed in claim 14, wherein said analog to digital converter (205) being communicatively coupled with said peak detection unit (204) for processing of said sampled ion current signal.

17. The method as claimed in claim 10, wherein fetching of said predetermined threshold for said sampled ion current signal being done by said peak detection unit (204), said fetching of threshold being from a look up table, said lookup table being configured based on an engine rpm and engine load, said look up table being prestored inside memory of said controller unit (200’).

18. The method as claimed in claim 11, wherein indication of said occurrence of the misfire being based on said misfire flag by a notification unit (207).

19. A vehicle for determining occurrence of a misfire or a no misfire in an engine, said vehicle comprising:
an ignition coil (101 and 103);
a spark plug (106); and
a controller unit (200’)
wherein,
said controller unit (200’) comprises of an ion current measurement circuit (107) for measuring an ion current signal in said ignition coil (101 and 103), said ion current signal being generated during a spark event in said spark plug (106),
said controller unit (200’) comprising of a sampling unit (205), said sampling unit (205) being configured for sampling said ion current signal, and
said controller unit (200’) comprising of a peak detection unit (204), said peak detection unit (204) being capable of determining an occurrence of one of a misfire and a no-misfire in said engine, based on detection of at least one peak in said sampled ion current signal.