WO2013118151A2

WO2013118151A2 - A system and method for controlling the ignition timing of an internal combustion engine

Info

Publication number: WO2013118151A2
Application number: PCT/IN2013/000087
Authority: WO
Inventors: Amit Dixit; Shashikanth Suryanarayanan; Pushkaraj Panse
Original assignee: Sedemac Mechatronics Pvt Ltd
Priority date: 2012-02-09
Filing date: 2013-02-08
Publication date: 2013-08-15
Also published as: WO2013118151A3

Abstract

A system and method of calculating ignition timing of a spark-ignited internal combustion engine that results in optimal operation of engine while ensuring suitable knock margin is provided. A base ignition timing σ_base is calculated using engine operating parameters, an additional ignition timing σ_ssc is calculated using an adaptive slope-seeking controller and a resultant ignition timing is calculated using the two calculated ignition timings. The operation of the slope-seeking controller (82) is controlled based on engine operating conditions.

Description

TITLE OF THE INVENTION

A system and method for controll ing the ignition timing of an internal combustion engine

FIELD OF THE INVENTION

The present invention relates a system and method for control ling ignition timing of an internal combustion (IC) engine. Particularly, it relates to a system and method for controlling i gnition tim ing of a spark-ign ited internal combustion engine that results in optimal operation of engine whi le ensuring su itable knock margin.

BACKGROUND OF THE INVENTION

Spark-ignited IC engines are widely used as prime movers for applications such as transport and power generation. These engines convert chem ical energy stored in a fuel such as gasol ine into useful mechanical work. Control of spark-ignited IC engines has been an active area of research for many decades.

For spark-ignited IC engines, the ign ition timing, that is the precise time at which a spark event that triggers combustion occurs, is an important control parameter that governs the efficiency of engine operation. For optimal engine operation, the ignition tim ing needs to be accurately controlled and varied suitably in response to engine operating conditions such as engine speed, load and engine temperature. The most prevalent method of controll ing spark-ignited IC engines in practice is to use a set of sensors for interpreting engine operating conditions, and choose ignition timing based on such interpreted engine operating conditions using a pre-cal ibrated table stored in an electronic control unit that controls the ignition timing. The table stored in memory of the electronic control unit is constructed using a set of calibration experiments on a set of sample engines that are representative of engines on which such ignition system is to be deployed. This method has a drawback, namely that it does not account for variations in engine characteristics arising due to factors such as manufacturing variations, ageing of engine components and change in fuel quality. Due to the presence of such variations in engine characteristics, the ignition timing calculated using a pre-calibrated table may not lead to an optimal engine operation.

Methods of choosing ign ition timing in real-time using a sensor for detecting engine knock have been described, for example, in fol lowing patents: U.S. Pat. No. 4,445,479, U.S. Pat. No. 5, 144,928 and U.S . Pat. No. 4,583, 175. Such schemes provide a potential for more optimal engine operation, but at an expense of added cost of sensor and related circuitry.

The present techniques used in an IC Engine are briefly described with reference to the following description and the accompanying drawings, wherei n the same characters and numerals denote the same parts and wherein,

Figure 1 is a schematic illustration of an internal combustion engine, to wh ich embodiments of the present technique are applicable;

Figure 2 is a graphical representation of the variation in torque generated by an IC engine with respect to the ignition tim ing for a set of operating conditions;

Figure 3 is a graphical representation of the variation in torque generated by an IC engine with respect to the ignition tim ing for an operating condition that shows the knocking region; Figure 4 is a schematic representation of the ESC method; Figure 5 is a graphical representation that shows reduction in knock margin that results when ESC method is used for ignition timing control application;

Figure 6 is a schematic representation of the S lope Seeking Control (SSC) method;

Figure 7 is a graphical representation that shows how knock margin can be adjusted using di fferent target slope values when SSC method is used for ignition timing control of spark-ignited IC engines;

Figure 1 is a schematic il lustration of one cyl inder of a four-stroke spark-ignited internal combustion engine. It should be understood that a four-stroke internal combustion engine configuration has been il lustrated for the purpose of description only. The system and the method described in this i nvention are equally applicable to two-stroke spark-ignited i nternal com bustion engines. Returning to Figure 1 , when the intake valve 1 opens, a m ixture of air and fuel enters the cyl inder 2. The mixture is ignited by a spark initiated by the spark plug 3. The resulting explosive combustion drives the piston 4 downwards as v iewed in Figure 1 , rotating the crankshaft (not shown in Figure). When the exhaust valve 5 opens, the exhaust gases generated during combustion leave the cylinder. Thus the explosive combustion of a m ixture of air and fuel leads to generation of mechanical torque. The torque is subsequently transferred to the output shaft which is connected to load through appropriate transm ission system . For example, in an automobile, output shaft is connected to wheels through a transmission. In a generator set, the output shaft is connected to the shaft of an alternator through a transmission system .

The precise timing at which the spark is initiated by the spark plug 3 is control led by an Electronic Control Unit (ECU) 6. The ECU 6 comprises of an input interface 6a for processing of sensor signals, a CPU 6b, memory 6c and driver circuitry 6d to drive the ignition coil that energizes the spark plug. The ECU processes signals generated by multiple sensors such as engine speed sensor 7, wheel speed sensor 8, throttle position sensor 9, cylinder head temperature sensor 10, takes decision on when to actuate the spark and energizes the spark plug accordingly though the driving circuitry.

The torque generated by the engine is strongly influenced by the ignition timing. The variation in torque generated as a function of the ignition timing, in terms of degrees before top-dead-center, correspond ing to a set of engine operating conditions is graphically represented in F igure 2. Engine operating conditions can be characterized in terms of parameters such as engine speed, throttle opening and engine oi l temperature. As shown in Figure, the torque generated by the engine has an extremum relationship with respect to the ignition tim ing. Specifical ly, for a given engi ne operating condition, the torque is maximum for a specific value of the ignition tim ing. Also, as seen from the figure, the ign ition timing that maximizes the torque generated by the engine varies with variation in engine operating conditions. Hence, for optimal operating of the engine, the ign ition timing must be varied as a function of the engine operating conditions.

Figure 3 shows the engine torque as a function of ignition timing for an engine operating condition. As mentioned previously, engine output torque is maximum for a specific value of ignition timing. However, if ignition timing is increased beyond a certain value, a phenomenon known as engine knocking occurs. This phenomenon is extremely detrimental to life of the engine, and is highly undesirable. For a given engine operating condition, the difference between executed ign ition timing and the ignition timing at which the engine knocking starts appearing is known as knock margin. In a spark- ignited IC engine, it is desirable that there is sufficient knock margin avai lable under al l engine operating conditions.

For certain engine operating conditions such as high load conditions, ignition tim ing at which knock starts appearing is close to the ignition timing that leads to maximum engine torque. Under such conditions, if ignition tim ing is chosen to be the timing that results in maximum engine torque, the knock margin is greatly reduced. In certain extreme conditions, ignition timing at wh ich knock starts appearing can be less that the ignition timing at which the torque is maximum. Thus, it is not always desirable to operate the engine at the ignition timing that results in maximum torque output. This also indicates that there is a trade-off between engine output torque and knock margin. Further, the ignition timing at which knock starts appearing is a function of engine operating conditions such as cyl inder head temperature and atmospheric pressure. Considering these factors, in most practical applications ignition timing is chosen to be less that the ign ition timing that results in maximum output torque to provide sufficient knock margin. In many practical applications that uti lize spark-ignited IC engines, the common method of choosing the ignition timing corresponding to a given engine operating condition involves carrying out a number of cal ibration tests on a set of sample engines. From such calibration tests, the optimal value of the ignition tim ing corresponding to various engine conditions that lead to an appropriate trade-off between engine output torque and knock margin are determined and stored in the memory of the ECU in the form of a table. During actual operation, the engine operating conditions are determined by the ECU using one or more sensors. The stored value of the ignition timing corresponding to the measured engine conditions is then retrieved from memory and used.

However, due to several factors such as manufacturing variations, aging, change in fuel quality, undetected changes in engine operating conditions, using an ignition timing that was found from the calibration exercise may not lead to an optimal operation of the engine. The engine may operate with either too retarded ignition timing which resu lts in engi ne torque output to be considerably lower than the maximum possible engine torque, or with too advanced tim ing which results in poor knock margins or in extreme case in knocking of engine. Thus, a scheme that decides, in real-time, the optimal ignition timing corresponding to the given engine operating conditions is highly desirable.

A method of fi nding ign ition timing that is sometimes used in practice involves using a dedicated sensor for determining onset of engine knock. In this method, during operation of engine, ignition timing is increased till the output of knock sensor indicates onset of engine knock. When such a condition is detected, advance of ignition timing is stopped. This method can lead to more optimal engine operation as compared to more widely used method of determining ignition timing using cal ibration experiments, but it requ ires a dedicated sensor, additional circu itry and additional computational power for processing the sensor output. Th is may not be economical ly feasible in application such as smal l two-three wheeler veh icles, smal l cars and generator sets.

Extremum Seeking Control (ESC) is a technique described in "Real- Time Optimization by Extremum-Seeking Control " M. Krstic and K. B. Ariyitr, Wiley Interscience, 2003, for real-time optimal control of a system . The techn ique is applicable to a type of systems where the relationsh ip between the systems inputs and outputs exhibits an extremum characteristic. Appl ications of ESC for different types of systems, including ignition timing control of spark-ignited IC engines have been proposed in following patents: U.S. Pat. No. 7,457,619, U.S. Pat. No. 6,098,010, U.S. Pat. No. 6,522,991 , U.S. Pat.

App. No. US2010/0106328 and U.S. Pat. No. 7,698,05 1 . A schematic representation of the methodology is shown in Figure 4. As shown in the figure, Plant 20 is a system being controlled, which exhibits an extremum relationship between input u and output y. The ESC method consists of passing the output y of the controlled plant 20 through a washout filter 21 (i.e. a high-pass filter), multiply ing the output w of the washout filter 21 with a period ic perturbation signal m and integrating the product d. The input u to the plant is chosen as the scaled 23 version of output of the integrator 22 added together w ith the periodic perturbation signal m. It can be shown that in steady-state, the mean value of input u corresponds to the input value that leads to an extremum value of output y. Methods of using ESC have been proposed for many practical appl ications such as HVAC control, information network control and control of mechanical compressors. Additionally, methods based on ESC have been proposed in relation to IC engine control, for conducting engine calibration experiments, and for real-time control .

Figure 5 shows engine output torque as a function of ignition tim ing for an engine operating condition. Since relationship between ignition tim ing and output torque exhibits extremum characteristic, ESC technique can be appl ied for control of ign ition timing such that output torque is maximized . Using ESC method in such a manner wi ll result in execution of the ignition tim ing that result in maximum engine torque. However, as mentioned previously, in most operating conditions, choosing an ignition tim ing that results in maximum torque output results in poor knock margins, or in extreme cases in engine knocking, which is a highly undesirable phenomenon that reduces l ife of the engine. Thus, ESC is not suitable for control of ignition tim ing of spark-ignited IC engines.

The Slope Seeking Control (SSC) technique, described in "Slope-Seeking, a Generalization of Extremum Seeking " International Journal of Adaptive Control and Signal Processing, 2004, 18: 1-14, is a general ization of the ESC technique that is applicable to systems that have an extremum relationship between inputs and outputs. The SSC techn ique provides means of attaining a certain slope of the input- output relationship, rather than the extremum point which is attained by the ESC method. A schematic representation of the SSC method is shown in Figure 6. As shown in the Figure, the SSC method is similar to the ESC method with one major difference: the input to the integrator 22 is the signal d added with a suitably chosen offset o. This results in a choice of the system input that attains a target slope on the input-output relationship. Figure 7 shows how SSC method can be suitably applied for ignition tim ing control of spark- ign ited IC engines. As mentioned previously, S SC method al lows for attaining a specified slope of the input-output relationship. Referring to Figure 7, it can be seen that by keeping different values of target slope, knock margin can be suitable chosen. As shows in Figure 7, application of SSC control with target slope value of Target Slope 1 results in ignition timing σι . S imi larly, application of SSC control with target slope value of Target Slope 2 results in ignition timing σ₂. Thus, it is possible to choose a knock margin by suitably choosing a target slope value. This flexibi lity is not provided by the ESC method. Hence, SSC method is more su itable for real-time control of ign ition tim ing as compared to the ESC method. A lthough SSC method al lows for choosing an optimal ignition tim ing whi le incorporating desired knock margi n, it is not usefu l under all operating conditions seen in a practical application of an internal combustion engine such as a vehicle or a generator set. Under certain operating conditions such as engine idl ing and fast changes in engine speed, it is not necessary or even desirable to use the SSC method. For example, using the SSC method during engine idling may lead to unstable engine operation, which is undesirable. Thus, a practical method of ignition timing control that utilizes the SSC method requires a selective use of the SSC method under suitable engine operating conditions. Further, for optimal operation, the parameters used in SSC method may also need to be changed depending on engine operating conditions. A single set of parameters for the SSC method may not work under all operating conditions. OBJECTIVES OF THE INVENTION

An objective of the invention is to provide a system and method for controlling the ignition timing of a spark-ignited IC Engine which obviates the aforesaid drawbacks.

DESCRIPTION OF THE INVENTION

In order to achieve the aforesaid and other objectives, according to the invention, a system and method of calculating ignition timing of an IC Engine is disclosed. Base ignition timing is calculated using engine operating parameters, an additional ignition tim ing is calculated using an adaptive slope- seeking controller and a resultant ignition tim ing is calculated using the two calculated ignition ti mings. The operation of the slope-seeking control ler is control led based on engine operating cond itions.

These and other aspects, features and advantages of the invention wi l l be better understood with reference to the following description and the accompanying drawings, wherein the same characters and numerals denote the same parts and wherein,

Figure 8 is a schematic representation of a method for determ ining, in real time, ignition tim ing of a spark-ignition IC engine;

Figure 9 is a schematic representation of the internal operation of the Slope Seeking Controller block shown in Figure 8;

Figure 10 is an exemplary flowchart i ll ustrating the method used in SSC Control Parameter and Reset Control block of the method described in Figure 8; Figure 1 1 is a schematic representation of an experimental setup that can be used for determination of parameters o and ;

Figure 12 is an illustration of relationship between engine torque, experimental ly computed quantity μ and ign ition timing; Figure 13 is an exemplary flowchart illustrating the method used in a part of the method described in Figure 8, where engine speed is considered to be the only input avai lable for computation of ignition timing;

Figure 14 is a schematic representation of a system that implements real-time control of ignition tim ing for a spark-ign ited IC engine using method descri bed in this invention; and Figure 15 is a schematic representation of the method implemented in microcontrol ler shown in Figure 14.

Figure 8 describes schematical ly, a method for determining, in real-time, ignition timing of a spark-ignited IC engine. It is assumed that the ignition timing σ determined by the method is executed in an IC engine 84 through suitable means 85, and that output of a set of sensors that monitor engine operating parameters is processed through a sensor processing block 80 and is avai lable as an input. It is assumed that engine speed is one of the outputs of the sensor processor block 80. As seen from Figure 8, the method consists of three blocks: a Lookup Table block 81 that takes in engine speed, possi bly along with other processed engine operating parameters such as throttle opening, engine oil temperature and manifold absolute pressure, and determines a base value of ignition tim ing, cal led Cbase,' a Slope Seeking Controller block 82 that implements a type of slope-seeking control ler and a block 83 for controlling parameters and operation of Slope Seeking Controller block 82, called SSC Parameter and Reset Control. Operation of each block will subsequently be explained in detai l.

The Lookup Table block 81 implements a table lookup operation, where based on a set of processed sensor values that indicate engine operating conditions, an ignition timing value is retrieved from a pre-cal ibrated table. Several possibilities exist regarding size and number of inputs of the lookup table. As an example, the table may have engine speed and throttle openings as inputs. Alternatively, the table may have only engine speed as an input. Ignition timing values as a function of the inputs are determ ined in advance, and are stored in the lookup table. When engine is running, a value of ignition timing corresponding to the inputs to the table is retrieved. Suitable interpolation operations may also be performed on the retrieved values. The output of the block is a base value of ign ition tim ing, cal led Obase-

Figure 9 shows a schematic representation of the internals of the Slope Seeking Control ler block. The block 82 takes engine speed as an input, and gives an ignition timing value, cal led ossc as output. As shown in Figure, engine speed is passed through a high-pass filter (HPF) 90 to generate signal x l , which is multiplied by a signal x2 to generate signal x3. S ignal x2 is a phase-delayed version of a periodic perturbation signal m, delayed by a phase Δ. In accordance with a target slope, an offset o is subtracted from signal x3 to generate signal x4. Signal x4 is passed through an integrator 91 to generate signal x5. S ignal x5 is scaled by the Scal ing block 92 by a factor to generate signal x6. S ignal x6 is passed through a Saturation block 93 that restricts value of signal x6 between two pre-defined l imits to generate signal x7. Signal x7 is added with the period ic perturbation signal m to generate the output esse of the block 82. The value stored in integrator 91 can be reset, that is set to be equal to zero, using a Reset Command signal 94. The Reset Command signal 94 is generated by the SSC Parameter and Reset Control block 83. The operation of the Slope Seeking Control block 82 can be characterized by parameters K, Δ and o. These parameters as wel l as overall operation of the block is controlled by the SSC Parameter and Reset Control block 83.

SSC Parameter and Reset Control block 83 governs the operation of the Slope Seeking Control block 82. The block 83 takes in a set of engine operating parameters as inputs. Broadly, it performs the fol lowing functions: it decides the parameters K, Δ and o of the Slope Seeking Control block 82; it decides whether the Slope Seeking Control block 82 needs to be executed and it decides when to reset the integrator 91 used in Slope Seeking Control block 82. A flow-chart representation of the operation of the block is shown in Figure 10. It is assumed that the sequence of operations defined in the flow-chart is repeated periodical ly. In the first step (SO I ), engine operating condition is determined based on values of engine operating parameters. Determination of engine operating condition is required, since in certain engine operating conditions, it may not be necessary, or even desirable to execute the Slope Seeking Control block. Examples of such conditions are engine idling, rapid accelerations/decelerations and transmission ratio shifts in automobi les equipped with stepped transmission. It needs to be ensured that under such conditions, the Slope Seeking Control block is not executed. Referring to Figure 10, based on operating condition of the engine, in step S02 it is decided whether to execute computations related to the Slope Seeking Control block. If it is decided that the computations related to the Slope Seeking Control block are not to be executed, then in step S03 integrator used in Slope Seeking Control block is reset, and value of aSSC is set to zero. Alternatively, if it is decided in step S02 that the computations related to Slope Seeking Control block are to be executed, then in step S04 vlaues of parameters K, Δ and o are determined based on values of engine operating parameters. These parameters are then used in computations performed in Slope Seeking Control block. SSC Parameter and Reset Control block contains values of parameters , Δ and o stored as a function of engine operating parameters. A description of how to choose these values as a function of engine operating parameters wi ll now be provided.

Parameter Δ is required to account for the phase shift between modulation input (ignition timing) and engine speed at modulation frequency. Since the system from ignition timing input to engine speed output is dynamic in nature, the output corresponding to the modulation input wil l be shifted from modulation input by a few degrees. It is necessary to account for this phase sh ift appropriately, since a wrong choice of phase shift compensation can lead to slow convergence to optimal ignition tim ing, or in extreme case in instabi l ity of system. Speci fical ly, a sufficient condition to ensure stabil ity of system is that the resulting phase difference between the demodulation signal (x2 in F igure 9) and engine speed is less than 90 deg. The phase shift between modulation input and corresponding output is a function of the modulation frequency, and of the frequency response characteristics of the input-output system . When the dynamics corresponding to the IC engine system are fixed in nature, for example as in a generator set, the amount of this phase shift is fixed with respect to the engine operating parameters. During implementation, this fixed value of phase sh ift, which can be computed a-priori based on knowledge of system dynam ics, can be used. On the other hand, when the dynamics of the IC engine system are a function of engine operating conditions, this phase shi ft can be a function of engine operating parameters. An example of this kind is an automobile with multi-stepped transm ission, where the dynamics are a function of the transmission ratio. In this case, during implementation, the parameter Δ can be chosen based on engine operating parameters. The value of parameter Δ to be used in run-time can be found out a-priori based on knowledge of dynamics of the system. In the special case where the system dynamics are a function of engine operating conditions, but it is not possible to identify the relevant operating condition in run-time, for example due to lack of relevant sensors, a fixed value of 45 degrees can be used for parameter Δ. This is because the dynamic relationship between a change in ignition timing and a change in engine speed can be well-approximated by a first-order linear system, and it is well-known that for such a system, irrespective of the system parameters, the phase difference between the input and output is always between 0 degree and 90 degrees. Thus, when the parameter Δ is chosen to be 45 degrees, it is ensured that the phase d ifference between the demodulation signal and the engine speed component corresponding to modulation is less than or equal to 45 degrees, which is a sufficient condition. for system stabi l ity. Thus, setting value of parameter Δ to 45 degrees ensures stable system operation in presence of changing system dynamics even when relevant operating conditions cannot be detected. Choice of parameter "o" decides the target slope between the torque and ignition tim ing, which in turn decides the knock margin. Parameter "o" can be chosen by conducting controlled experiment on the target engine system . A schematic diagram of the experimental setup that can be used for this purpose is shown in Figure 1 1 . As shown in the figure, the experimental setup consists of means of varying load on engine to maintain the speed of engine at a constant level, means of executing ignition tim ing at desired level, where ignition timing consists of a freely settable mean value with a freely settable modulation component added to it, and means of computing a quantity μ based on measured engine speed and modulation part of ignition timing. The calculated value of μ corresponds to the slope of relationship between engine torque and ignition timing. By conducting experiments at different constant speeds and different constant throttle openings, the value of μ for different values of ignition tim ing can be calcu lated. An i llustration of relationship between engine torque, value of μ and mean ignition timing for a constant engine speed for two different throttle openings is shown in F igure 12. As seen from the Figure, the value of parameter "o" can be chosen from such observed relationship as the value of μ that leads to an acceptable lowering of engine torque. The value of parameter "o" can thus be calibrated for a combination of engine speeds and throttle opening values, and stored in a table during run-time implementation. Alternatively, it can be observed from Figure 12 that for constant engine speed, for a given distance from the ign ition timing that corresponds to the maximum torque, value of μ is lesser for higher throttle opening. Thus, for a given engine speed, choosing the value of "o" that corresponds to an acceptable lowering of engine torque for highest throttle opening wi ll lead to acceptable lowering of engine torque at any lower throttle opening. This characteristic can be used in implementations where the throttle position sensor is not avai lable, where the value of parameter "o" can be derived for highest throttle openings for a set of engine speeds, and stored as a function of engine speed alone. During run-time, the value of parameter "o" can be retrieved using the prevalent engine speed.

Value of parameter K decides the rate of convergence of ign ition tim ing to the target ignition timing value. Value of parameter K can also be found from experiments conducted for determi ning values of parameter "o". Speci fically, referring to Figure 12, value of parameter , and the d ifference (μ - o) decides the system convergence rate. Since μ and o are known, value of can be chosen to be the value that wi ll lead to an acceptable rate of convergence. A set of values of K can thus be determined as a function of engine speed and throttle positions. During implementation, based on prevalent values of engine speed and throttle position, the value of K can be selected from a stored table. Further, similar to choice of parameter "o", for a given engine speed, value of difference (μ - o) is lowest for highest throttle opening. Consequently, if the value of K derived for highest throttle opening is used for a lower throttle opening, the convergence rate wi ll be better than the convergence rate at highest throttle opening. This characteristic can be used in implementations where the throttle position sensor is not available, where the value of parameter can be derived for highest throttle openings for a set of engine speeds, and stored as a function of engine speed alone. During run-time, the value of parameter K can be retrieved using the prevalent engine speed.

Method described in F igure 8 enables optimal operation of a spark-ign ited IC engine whi le preserving a suitable knock margin. It addresses variations in engine characteristics arising due to factors such as aging, change in fuel qual ity and manufacturing variations by suitable changing ignition tim ing in real-time operation. The method also prevents undesirable ignition timing changes that may occur in SSC technique when engine is undergoing fast changes in operating conditions. Further, optim ization of ign ition timing is not performed under conditions where such optimization is not required, such as during engine idl ing. An embodiment of the method described above will now be presented . In this embodiment, engine speed is considered to be the only available Engine Operating Parameter input for computation of ign ition ti m ing. In this embodiment, the Lookup Table block (shown i n Figure 8) consists of a one dimensional lookup table that speci fies the base ign ition timi ng Obase as a function of engine speed . The Slope Seeking Control block remains identical to one shown in Figure 9, A flow-chart representation of the SSC Parameter and Reset Control block is shown in Figure 13. As shown in Figure 13, the first step SO I of the SSC Parameter and Reset Control block is to check whether the engine speed (denoted as RPM in Figure 1 3) is less than a predetermined value, called RPMjdi_e- If this cond ition is found to be true, then it is concluded that engine is under idl ing conditions. Accordingly, in step S04 the integrator used in the Slope Seeking Control block is reset, and ignition timing ossc is set to zero. In step SO I , i f engine speed is found to be higher than the predeterm ined engine speed RPM,di_e, then in step S02 the time derivative of engine speed, dRPM, is calculated. In step S03, it is checked whether absolute value of dRPM is higher than a predeterm ined value, dRPM|_ini,_t. If th is condition is found to be true, then it is concluded that fast transients in engine operation is taking place. Accordingly, step S04 is executed as mentioned earl ier. If in step S03 , absolute value of dRPM is found to be less than the predetermined value dRPMiimn, then in step S05 the Slope Seeking Control block parameters , Δ and o are computed as functions of engine speed. Using the method described in above embod iment, an optimal ign ition timing for a spark-ignited

1C engine can be calculated using only engine speed as input.

Figure 14 describes a system that implements real-time optimal control of ignition timing of a spark-ignited IC engine using the method described in this invention. As shown in Figure, there are three main components of the system 140. The first component is a signal processing circuitry 141 that interfaces with a set of available sensors, and generates signals that can be accepted by a m icrocontrol ler 142. The second component is a microcontroller 142 accepts the signals generated by the signal conditioning circuitry , executes the method and generates command signals for the ignition driver circuitry 143. The third component is an ignition driver circuitry 143 that energizes the ignition coi l to generate spark in IC engine in response to commands received from the microcontrol ler 142. Figure 15 describes schematical ly the method executed by the m icrocontrol ler shown in Figure

14. The first part of the method reads the sensor signals processed by the signal conditioning circuitry 150 and generates signals representing engine operating parameter 152 that are used by the ignition timing calculation block 151. The optimal ignition timing calculation block 151 contains the method that performs computations according to the method described in Figure 8 to calculate optimal ignition timing σ. The tim ing computation block 153 takes the ignition timing σ and a processed sensor signal corresponding to crankshaft position as inputs. Based on ignition timing to be executed, and using crankshaft position as reference, it generates command signals which are given to the driver circuitry to execute sparking events at appropriate crankshaft positions.

It should be noted that the system described in Figure 14 can be used in any one of the two commonly used configurations of ignition system hardware, the capacitive discharge ignition and the transistorized ignition. The capacitive discharge ignition uses energy stored in a capacitor to prov ide the sparking energy, while a transistorized ignition uses energy stored in an inductor to provide the sparking energy. According to the type of ign ition system hardware chosen, the ign ition driving circuitry and the timing command computation methods wil l need to be suitably chosen.

It should be noted that the system described in th is invention can either constitute a stand-alone ignition system, such as one used in many carburetted IC engines, or can be part of an overal l engine management system such as one used in IC engines equ ipped with an electronic fuel-injection system .

The system described in this invention can be used when a crankshaft position transducer is the only available sensor. In such condition, crankshaft position transducer can be used for computation of engine speed. Using engine speed, optimal ignition timing can be computed as shown in Figure 13. Using ignition tim ing so calculated, and using output of the crankshaft position transducer, appropriate tim ing commands can be generated for the ignition driving circuitry.

Although the invention has been descri bed with reference to a specific embod iment, this description is not meant to be construed in a limiting sense. Various modifications of the disclosed embodiment, as well as alternate embodiments of the invention, wil l become apparent to persons skil led in the art upon reference to the description of the invention. It is therefore contemplated that such mod ifications can be made without departing from the spirit or scope of the invention as defined.

Claims

CLAIMS:

1. A system for controlling ignition timing of a spark-ignited internal combustion engine (84) comprising:

a) plurality of sensors connected to said internal combustion engine;

b) a sensor processing circuitry (141) processing output from said sensors in a microcontroller acceptable form;

c) a microcontroller (142) processing output from said sensor processing circuitry (141) executing a method comprising the steps:

i. computing a set of engine operating parameters (150; 152) indicative of engine operating conditions based on outputs of sensor processing circuitry (141);

ii. determining a base ignition timing Obase using said engine operating parameters (150; 152) and a pre-calibrated table (81);

iii. determining engine operating conditions based on said engine operating parameters (150; 152); iv. deciding if slope-seeking controller (82) computations are to be performed for said engine operation conditions determined in step (iii);

v. determining parameters to be used in said slope-seeking controller (82) based on engine operating parameters (150; 152);

vi. performing slope-seeking controller computations (83) based on slope-seeking controller parameters determined in step (v) to compute an ignition timing assc;

vii. adding the base ignition timing Ob_aSe and the ignition timing assc to compute the resultant optimal ignition timing σ; vii i. generating command signals for an ignition driving circuitry based on ignition timing calculated in step (viii) and on output of the position transducer, output of which can be related to crankshaft position; d) an ignition driving circuitry ( 143) connected to said m icrocontroller ( 142) for generating a spark in the internal combustion engine (84),

A system as claimed in claim 1 wherein if slope-seeking control ler computations are not to be performed in step (b)(iv) as claimed in claim 1 , integrator used in said slope-seeking controller is reset and assc is set to zero.

A system as claimed in claims 1 or 2, wherein said ignition driving circuitry ( 143) uses energy stored in a capacitor to provide a spark.

A system as claimed in claims 1 or 2, wherein said ignition driving circuitry ( 143) uses energy stored in an inductor to provide a spark.

A system as claimed in claim 1 , wherein said sensor processing circuitry includes a position transducer to indicate operating condition of said internal combustion engine (84).

A method for controll ing the ignition timing of a spark-ignited internal combustion engine (84) comprising the steps of: a) determining a base ignition timing a_base using a set of engine operating parameters (150; 152) and a pre-calibrated table (81);

b) determining engine operating conditions based on engine operating parameters (150; 152);

c) deciding (142) if slope-seeking controller (82) computations are to be performed for the engine operation conditions determined in step (b);

d) determining parameters (83) to be used in a slope-seeking controller (82) based on engine operating parameters (150; 152);

e) performing slope-seeking controller computations (142) based on slope-seeking controller parameters (150; 152) determined in step (d) to compute an ignition timing esse;

adding the base ignition timing Ob_aSe and the ignition timing ossc to compute the resultant optimal ignition timing σ.

7. A system as claimed in claim 6, wherein if slope-seeking controller computations are not to be performed in step (b)(iv) as claimed in claim 6, integrator used in said slope-seeking controller is reset and ossc is set to zero.

8. A method as claimed in claim 6 or 7, wherein engine speed is the only engine operating parameter (150; 152) used for calculation of ignition timing.