JP2007332934A - Optimal ignition timing setting method of spark ignition internal combustion engine and optimal ignition timing setting device of spark ignition internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To set the optimal ignition timing of a spark ignition internal combustion engine of reflecting an operation condition and an operation state of an internal combustion engine. <P>SOLUTION: This method for determining the optimal ignition timing, delays the ignition timing little by little from an initial value SA<SB>1</SB>(S10 and S12), and determines an average indicator characteristic curve and torque τ in its ignition timing advance angle by performing combustion simulation (S14), and determines whether or not knocking is caused by using an ignition timing predicting technique (S16 and S18), and sets the optimal ignition timing (S22) by the limit ignition timing of causing the knocking. Here, the ignition timing predicting technique (S16) starts the average indicator characteristic curve calculated by the combustion simulation, and predicts the existence of the occurrence of knocking on its ignition timing, by using a cycle variation mode, a self-ignition predicting model and a knock determining value variation model. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an optimal ignition timing setting method for a spark ignition internal combustion engine and an optimal ignition timing setting device for a spark ignition internal combustion engine, and more particularly to a spark ignition internal combustion engine for obtaining an optimal ignition timing using a calculation model and simulation. The present invention relates to an optimum ignition timing setting method and an optimum ignition timing setting device for a spark ignition type internal combustion engine.

  In a spark ignition type internal combustion engine, increasing the compression ratio is effective for improving thermal efficiency, but the occurrence of knocking is counted as one of the impeding factors. Therefore, attempts have been made to provide knock sensors in the engine to detect the occurrence of knocking and perform feedback control at the ignition timing, and this mechanism has already been incorporated into many engines. Thus, not only the avoidance control is performed after the occurrence of knocking is detected, but also the occurrence of knocking is predicted according to a calculation model in order to more reliably avoid the knocking. Knocking is often simply referred to as knocking, and will be described as knocking or knocking below.

  For example, Patent Literature 1 discloses a combustion control device that predicts and controls the occurrence of knocking in a spark ignition internal combustion engine using a calculation model. Here, the combustion chamber is basically based on a two-region model that is divided into an unburned part and a burned part with the flame front as the boundary, and each state value estimated from information on the operating state of the engine is used as an initial value, and energy related to combustion is determined. It is stated that conserving equations etc. are used, and the mass ratio of the burned part is a function of the crank angle in the Wiebe function form, and the equation is solved according to the crank angle to predict the state change of the unburned part / burned part. It has been. Then, this simulation is applied to the self-ignition model to estimate the knocking intensity by predicting the self-ignition generation time of the unburned gas and the amount of heat generated by the self-ignition, and the combustion control so that the knocking intensity is below a predetermined value. Is done.

  Three self-ignition models are described here. One is to calculate the ignition delay time from the temperature and pressure of the unburned gas at a certain point of time based on an equation that gives the ignition delay time when the unburned gas is at a predetermined temperature and pressure. Ignition occurs. The equation for the ignition delay time used here is an exponential function for the reciprocal temperature (1 / T) and a function of the power of (−n) for the pressure. The second auto-ignition model uses the Live-Good-Wu integral considering that the ignition delay time changes with the passage of time, finds the ignition delay time under that state from the temperature, pressure, etc. at a certain moment, It integrates over time, and self-ignition occurs when the integral value becomes 1. In the third auto-ignition model, a gas in a fuel chamber is a gas in which a chemical species i is mixed at a mass fraction yi, and a chemical element in which the mass fraction yi of the chemical species i changes as the reaction proceeds. Based on the reaction model, this predicts changes in the temperature and pressure of the unburned gas over time, and self-ignition occurs when the temperature of the unburned gas section exceeds a predetermined value. .

JP 2004-332584 A

  In Patent Document 1, several self-ignition models are used, and the knocking strength is estimated by predicting the self-ignition occurrence time of unburned gas and the amount of heat generated by self-ignition, and combustion is performed so that the knocking strength becomes a predetermined value or less. It is stated that control takes place. Here, the simulation is performed with each state value estimated from the information on the operating state of the engine as an initial value. What is closely related to the occurrence of knocking in the engine operating state is the relationship between the crank angle and the pressure in the cylinder, and this is generally called a finger pressure history or simply finger pressure.

  In general combustion simulations of internal combustion engines including Patent Document 1, an average acupressure history is used as an acupressure history that is the basis of calculation. The average acupressure history is a typical acupressure history when the operating conditions of the internal combustion engine are given, but the actual operating conditions of the internal combustion engine vary considerably, and the acupressure history under the same operating conditions is also considerable. There is a cycle fluctuation. Knocking is more likely to occur when the pressure of the acupressure history is higher, but since the average acupressure history is used in the prior art, the occurrence of knocking is evaluated to be lower. That is, from the viewpoint of improving the compression ratio, the safety side is opposite to the safety side.

  In Patent Document 1, the first and second auto-ignition prediction models use ignition delay times calculated based on an equation that gives an ignition delay time when the unburned gas is in a predetermined temperature and pressure state. . The equation for the ignition delay time used here is an exponential function for the reciprocal temperature (1 / T) and a function of the power of (−n) for the pressure. Therefore, the temperature, that is, the in-cylinder temperature and the pressure, that is, the finger pressure, are considered on the assumption of the above function form. However, in the actual driving situation, the self-ignition delay time varies depending on the driving conditions, and The ignition delay time may not follow the function form as described above.

  As described above, the conventional technology may not reflect the cycle fluctuations and the self-ignition delay time that occur in the actual operating state of the internal combustion engine, and the self-ignition timing is not accurately estimated, so that knocking is suppressed. The optimal ignition timing setting is incorrect.

  An object of the present invention is to provide an optimum ignition timing setting method for a spark ignition type internal combustion engine and an optimum ignition timing setting device for a spark ignition type internal combustion engine reflecting the operating conditions and operating conditions of the internal combustion engine.

  An optimal ignition timing setting method for a spark ignition type internal combustion engine according to the present invention, for a spark ignition type internal combustion engine, gives an ignition timing under an arbitrary operating condition, executes a combustion simulation, and under the ignition timing, Calculating an average acupressure characteristic curve indicating the relationship of the average acupressure to the crank angle, obtaining a knock possibility acupressure characteristic curve that may be knocked from the calculated average acupressure characteristic curve, and a knocking possibility acupressure characteristic curve The combustion simulation is performed under the conditions satisfying the conditions, the mass combustion ratio characteristic curve and the in-cylinder temperature characteristic curve with respect to the crank angle are calculated, the temperature based on the knock possibility acupressure characteristic curve and the in-cylinder temperature characteristic curve A process for determining the autoignition timing according to a predetermined autoignition prediction model using an ignition delay time that is a function of pressure, and a mass combustion ratio characteristic curve Including a knock presence / absence determination step of determining whether or not knocking has occurred based on the determined self-ignition mass combustion ratio, which is a mass combustion ratio corresponding to the self-ignition timing, and changing the ignition timing. The ignition timing at the limit of occurrence of knocking is set as the optimal ignition timing.

  Further, in the optimum ignition timing setting method for a spark ignition type internal combustion engine according to the present invention, the step of obtaining a knock possibility acupressure characteristic curve includes the acupressure characteristic curve under a cycle variation stored in advance with respect to the average acupressure characteristic curve. It is preferable to search for a group, identify a maximum acupressure characteristic curve showing the maximum acupressure characteristic among them, and use this as a knock possibility acupressure characteristic curve.

  Further, in the optimum ignition timing setting method for a spark ignition type internal combustion engine according to the present invention, the step of obtaining the self-ignition timing is a self-ignition in which the change in the ignition delay time with respect to the temperature is less in the intermediate temperature region than in the temperature regions before and after the intermediate temperature region. It is preferable to determine the autoignition timing using a prediction model.

  Further, in the optimum ignition timing setting method for a spark ignition type internal combustion engine according to the present invention, the ignition delay time is the magnitude of the finger pressure, the in-cylinder temperature, the value of (theoretical air / fuel ratio / actual air / fuel ratio), or the octane number. Alternatively, it is preferable to determine the autoignition timing as at least one function of the residual gas amount.

  Further, in the optimum ignition timing setting method for a spark ignition type internal combustion engine according to the present invention, the knock presence / absence determination step compares the calculated self-ignition mass combustion ratio with a predetermined knock generation mass combustion ratio, It is preferable to determine the presence or absence of occurrence.

  Further, the optimum ignition timing setting method for a spark ignition type internal combustion engine according to the present invention is a spark ignition type internal combustion engine, which performs an ignition timing under an arbitrary operating condition to execute a combustion simulation, and sets the initial ignition timing and torque. A step of giving a value, advancing the ignition timing of the initial value, and executing a combustion simulation to calculate a torque under the advanced angle and an average acupressure characteristic curve with respect to the crank angle, A process of searching a previously stored acupressure characteristic curve group under a cycle variation for the average acupressure characteristic curve and specifying a maximum acupressure characteristic curve indicating the maximum acupressure characteristic curve as a knocking possibility acupressure characteristic curve And a combustion simulation under conditions satisfying the knock potential acupressure characteristic curve, a mass combustion ratio characteristic curve with respect to the crank angle, an in-cylinder temperature characteristic curve, and A step of calculating, a step of obtaining a self-ignition timing based on a predetermined self-ignition prediction model using a ignition delay time as a function of temperature and pressure, based on a knock possibility acupressure characteristic curve and an in-cylinder temperature characteristic curve, and a mass combustion ratio The mass combustion ratio corresponding to the self-ignition timing is obtained from the characteristic curve, compared with a predetermined knock generation mass combustion ratio, and when knock occurs in the knock presence / absence determination step and the knock presence / absence determination step for determining whether or not knock occurs. When determining, and when the torque obtained in the advance step is equal to or lower than the torque before advance, an optimal ignition timing setting step in which the ignition timing before performing advance in the advance step is the optimum ignition timing; In the knock presence / absence determining step, if it is not determined that knocking occurs, the process returns to the advance step, further advanced, and the subsequent steps are repeated.

  An optimum ignition timing setting device for a spark ignition type internal combustion engine according to the present invention is an optimum ignition timing setting device for obtaining an optimum ignition timing for a spark ignition type internal combustion engine by a computer. Under the operating conditions, the ignition timing is given to execute the combustion simulation, the processing means for giving the ignition timing and the initial value of the torque, the initial ignition timing is advanced, the combustion simulation is executed, and the Advancing processing means for calculating an average acupressure characteristic curve with respect to the torque below and a crank angle, and searching for an acupressure characteristic curve group under a cycle variation stored in advance with respect to the calculated average acupressure characteristic curve, The processing means for specifying the maximum acupressure characteristic curve showing the maximum acupressure characteristics as the knock possibility acupressure characteristic curve and satisfying the knock possibility acupressure characteristic curve A combustion simulation is executed under the conditions, a processing means for calculating a mass combustion ratio characteristic curve with respect to the crank angle and an in-cylinder temperature characteristic curve, a temperature based on a knock possibility acupressure characteristic curve and an in-cylinder temperature characteristic curve. Processing means for determining the autoignition timing according to a predetermined autoignition prediction model using an ignition delay time that is a function of pressure, a mass combustion ratio corresponding to the autoignition timing from the mass combustion ratio characteristic curve, and a predetermined knock generation mass Compared with the combustion ratio, knock presence / absence determination processing means for determining the presence or absence of knock occurrence, and when determining that knock occurs in the knock presence / absence determination step, the torque obtained in the advance step is equal to or less than the torque before advance In the case of the above, a knocking presence / absence determination step, including an optimal ignition timing setting processing means for setting the ignition timing before the advance in the advance step to an optimal ignition timing Oite, if it is not determined that knocking occurs, the return to the advance process, and further advanced, and repeating the processes subsequent.

  According to at least one of the above-described configurations, an average acupressure characteristic curve is calculated under a given driving condition, and a knocking possibility acupressure characteristic curve that may be knocked is obtained with respect to the calculated average acupressure characteristic curve. Based on this knock possibility acupressure characteristic curve, a combustion simulation is executed and the like to determine the self-ignition timing, and the presence / absence of knocking is determined based on the mass combustion ratio at that timing. Then, the ignition timing is changed to set the ignition timing at the limit of knock generation as the optimum ignition timing.

  Thus, instead of using the average acupressure characteristic curve, that is, the average acupressure history, a knock possibility acupressure characteristic curve corresponding to the average acupressure history is obtained, and the self-ignition timing and the like are obtained. Therefore, it is possible to set the optimum ignition timing reflecting the actual operating conditions and operating conditions of the internal combustion engine.

  In addition, the acupressure characteristic curve for determining the knocking possibility is obtained by searching a group of acupressure characteristics under a cycle variation stored in advance for the average acupressure characteristic curve, and showing a maximum acupressure characteristic among them. This is done by specifying a curve. Therefore, it is possible to set the optimal ignition timing reflecting the cycle variation of the acupressure history in the actual operating conditions and operating conditions of the internal combustion engine.

  In addition, since the auto-ignition timing is calculated using an auto-ignition prediction model in which the change in the ignition delay time with respect to the temperature is smaller in the intermediate temperature region than in the temperature region before and after that, the auto-ignition delay time is simply calculated as Instead of using an exponential function, it is possible to set the optimal ignition timing by reflecting the change in the self-ignition delay time in the actual operating state of the internal combustion engine.

  Further, the ignition delay time is assumed to be a function of at least one of the magnitude of the finger pressure, the in-cylinder temperature, the value of (theoretical air / fuel ratio / actual air / fuel ratio), the octane number, or the residual gas amount. Therefore, it is possible to set the optimal ignition timing reflecting the actual operating condition of the internal combustion engine.

  In addition, the calculated self-ignition mass combustion ratio is compared with a predetermined knock generation mass combustion ratio to determine whether knock has occurred or not. It is known that knocking is more likely to occur as the mass combustion ratio during self-ignition is lower. If the operating conditions and the fluctuation conditions thereof are determined, the mass combustion ratio when knocking occurs can be predicted in advance. If the calculated self-ignition mass combustion rate is lower than the predicted knock generation mass combustion rate, knocking occurs. Therefore, by comparing the two, it is possible to know the autoignition timing at the limit of occurrence of knocking, and by setting this as the optimal ignition timing, the optimal ignition timing is set to reflect the actual operating conditions and operating conditions of the internal combustion engine. It becomes possible to do.

  Also, the ignition timing is given under arbitrary operating conditions, the combustion simulation is executed, the initial values of the ignition timing and torque are given, the ignition timing is advanced from the initial values, the average acupressure characteristic curve calculation, the maximum acupressure Perform characteristic curve specification, mass combustion ratio characteristic curve calculation, in-cylinder temperature characteristic curve calculation, self-ignition timing calculation, knock occurrence determination, etc. When the torque is not more than the pre-advance torque, the ignition timing before the advance is performed in the advance process is set as the optimum ignition timing. If it is not determined that knocking will occur, the angle is further advanced and the subsequent steps are repeated. Thus, the optimal ignition timing can be obtained based on the maximum acupressure characteristic curve by shifting the ignition timing. Therefore, it is possible to set the optimum ignition timing reflecting the actual operating conditions and operating conditions of the internal combustion engine.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The characteristic curves and the like illustrated below are used for convenience of explanation, and are characteristic curves having other characteristics as long as they reflect actual operating conditions and operating conditions of the internal combustion engine. It does not matter.

  FIG. 1 is a flowchart for explaining the principle flow of a method for obtaining the optimum ignition timing, and FIG. 2 is a flowchart for explaining the role of a model used in the principle flow. Note that a flowchart of a procedure specifically processed on the computer will be described in detail later.

As shown in FIG. 1, the optimum ignition timing is calculated by advancing the ignition timing little by little to determine whether or not knocking will occur by using an ignition timing prediction method. The optimal ignition timing is determined by the ignition timing. That is, under the operating conditions given engine in question, given the initial value SA ₁ of the ignition timing, it calculates the initial value tau ₁ of the torque by executing a combustion simulation in the ignition timing. In FIG. 1, the initial value of the given ignition timing is shown as SA ₀ , and the calculated initial value of the torque is shown as τ ₀ (S 6, S 8, S 10). Initial value SA ₁ of the ignition timing is the ignition timing is found that knocking does not occur. In general, it is known that the characteristics of the ignition timing and torque show the maximum torque at a certain ignition timing, and the knocking advances the ignition timing toward the ignition timing indicating the maximum torque. It is known to occur easily. Here, to advance the ignition timing is to set an ignition timing corresponding to a preceding angle in crank rotation, that is, a crank angle at a time earlier than the present time. On the other hand, setting the ignition timing corresponding to the crank angle at a later time than the present is called retarding the ignition timing. Therefore, the ignition timing SA ₁ = SA ₀ of the initial value is preferably retarded sufficiently.

  Then, the ignition timing is advanced by ΔSA to be SA (S12). A combustion simulation is performed under this advanced state, and the average acupressure characteristic, that is, a typical value of each acupressure, which is the in-cylinder pressure for each crank angle, is obtained, and the obtained acupressure characteristic curve is obtained. Then, the torque τ at the ignition timing SA is obtained (S14). As described above, the acupressure characteristic is a characteristic curve in which the horizontal axis represents the crank angle and the vertical axis represents the acupressure, and indicates the change history of the in-cylinder pressure of the internal combustion engine as the crank rotates. Called history. Various combustion simulation programs for obtaining an average acupressure characteristic curve, that is, an average acupressure history, have already been proposed, and an appropriate one can be used among them.

When the average acupressure characteristic curve is obtained, an ignition timing prediction method is used based on the average acupressure characteristic curve (S16), and it is determined whether or not knocking occurs under the advance angle SA, thereby further increasing the ignition timing. It is determined whether or not to perform (S18). The result of the prediction of S16, it is determined that knocking occurs, the ignition timing SA ₁ before advance so that the optimum ignition timing SA ^* (S22).

As described above, the setting of the initial value SA ₁ = SA ₀ is sufficiently retarded from the ignition timing indicating the maximum torque. Therefore, if the advance angle magnitude ΔSA is appropriate, it is usually determined that there is no knock. Further, the torque τ at that time is larger than the torque τ ₁ before the advance angle. Therefore, in the determination (S20) of whether τ is larger than τ ₁ or not, it is determined that there is no knocking except that τ is not larger than τ ₁ , and the advanced SA state is replaced with the initial value. (S24), the process returns to S12 again. That is, the ignition timing is further advanced by ΔSA. The subsequent processing is repeated. When the ignition timing is successively advanced, so gradually knocking is likely to occur, with the advanced state of SA ₁ before the advanced state knocking is first generated and the optimum ignition timing SA ^*. May tau is not determined to be greater than tau ₁ at S20, with the advanced state of SA ₁ before the advanced state, is the optimum ignition timing SA ^*. In this way, the ignition timing is advanced little by little to determine whether or not knocking occurs using the ignition timing prediction method, and the optimum ignition timing can be determined by the limit ignition timing at which knocking occurs. .

  FIG. 2 shows a detailed internal flowchart of the ignition timing prediction method (S16). The ignition timing prediction method starts from the average acupressure characteristic curve calculated by the combustion simulation, and uses a cycle fluctuation model, a self-ignition prediction model, and a knock judgment value fluctuation model to predict the presence or absence of knocking for the ignition timing. is there.

  The cycle variation model is obtained by modeling a variation in the acupressure history of, for example, 400 cycles under a given driving condition and associating it with an average acupressure characteristic curve under the driving condition. This cycle variation model is created for each operating condition and stored in an appropriate storage device, and can be searched using the average acupressure characteristic curve as a search key.

  The self-ignition prediction model is used when calculating the self-ignition timing and the mass combustion ratio at that time using the history of mass combustion ratio and in-cylinder temperature obtained by performing a combustion simulation based on the acupressure characteristic curve. It is a model of when self-ignition occurs. Here, the second self-ignition model of Patent Document 1 is used in an improved manner. The second self-ignition model of Patent Document 1 uses the Liven Good-Wu integral considering that the ignition delay time changes with time, and obtains the ignition delay time under that state from the temperature, pressure, etc. at a certain moment. The reciprocal is integrated over time, and self-ignition occurs when the integral value becomes 1. In Patent Document 1, an expression defining the ignition delay time f is an exponential function for the reciprocal of temperature (1 / T) and a function of the power of (−n) for pressure. As will be described later in detail, the self-ignition prediction model in FIG. 2 adapts the function form of temperature to an actual one, and uses the effect of operating condition parameters other than temperature and pressure. The self-ignition prediction model considering the effect of these parameters is stored in an appropriate storage device, and the ignition delay time f can be read using one or a plurality of parameters as a search key.

  The knock determination value variation model is obtained by modeling the mass combustion ratio when knocking occurs. Here, the mass combustion ratio is defined by (calorific value up to the present) / (low calorific value of the total amount of injected fuel). Here, the lower calorific value is a calorific value in the case where moisture remains as a gas (water vapor), and corresponds to a heat amount that can actually be used, that is, a so-called true calorific value. The unit is J / kg. The total calorific value is calculated based on the amount of fuel introduced. As understood from the unit, the calorific value is related to the combustion mass, and from that point of view, it is called the mass combustion ratio. The mass combustion ratio is also called BMF (Burned Mass Fraction).

  Generally, it is known that knocking is more likely to occur as the mass combustion rate is lower, and the mass combustion rate at which knocking occurs can be determined according to the operating conditions. Therefore, knock determination can be made by comparing the mass combustion ratio at which knocking occurs with the mass combustion ratio at the self-ignition timing. The knock determination variation model is a model from such a viewpoint.

  Returning to FIG. 2, in the ignition timing prediction method (S16), first, an average acupressure characteristic curve is given (S30). Next, a cycle variation model corresponding to the average acupressure characteristic curve is acquired (S32). And the acupressure characteristic curve with a possibility of knocking is specified from among a plurality of acupressure characteristics curves included in the acquired cycle variation model. In general, since the higher the acupressure, the easier it is to knock, the acupressure characteristic curve among the plurality of acupressure characteristics curves included in the cycle variation model is specified as a possibility of knocking (S34).

  Under the conditions of this maximum acupressure characteristic curve, the history curve of the mass combustion rate, the history curve of the in-cylinder temperature, that is, the characteristic curve indicating the change in the mass combustion rate with respect to the crank angle, and the change in the in-cylinder temperature with respect to the crank angle are also shown. Is obtained (S36).

  Then, based on the maximum acupressure characteristic curve and the in-cylinder temperature characteristic curve, the time lapse, that is, the ignition delay time f corresponding to the crank angle is calculated. Since the ignition delay time f is modeled for each parameter of the operating condition as described above, the ignition delay time f can be obtained with the passage of time using each parameter as a search key. Then, the Live-Good-Wu integration is executed, and the time when the integrated value becomes 1 is the self-ignition timing tk. Then, a mass combustion ratio pBMF corresponding to tk on the mass combustion ratio characteristic curve is obtained (S38).

  Then, according to the knock determination value variation model, the kBMF to be knocked is compared with the pBMF obtained in S38 (S42), and the presence or absence of the knock is determined. In this way, it is possible to predict the occurrence of knocking for the ignition timing using the cycle variation model, the auto-ignition prediction model, and the knock determination value variation model, starting from the average acupressure characteristic curve calculated by the combustion simulation. .

  FIG. 3 is a block diagram showing the configuration of the optimum ignition timing setting device 10 for the spark ignition type internal combustion engine. The optimal ignition timing setting device 10 is a device having a function of obtaining an optimal ignition timing using a calculation model, simulation, and the like, and outputs a CPU 12, an input unit 14 such as a keyboard for inputting initial conditions, and the like, a calculation result, and the like. An output unit 16 such as a printer or a display and a storage unit 18 for storing a calculation model, a program, and the like are included. These elements are connected to each other via an internal bus. The optimum ignition timing setting device 10 can be constituted by a personal computer or a scientific computer suitable for simulation.

  The storage unit 18 stores the cycle variation model 34, the self-ignition prediction model 36, the knock determination value variation model 38, the combustion simulation program 40, and the like described with reference to FIG. As described above, the cycle variation model 34 can retrieve a plurality of acupressure characteristics curves according to the corresponding cycle variation, using the average acupressure characteristic curve as a search key, and particularly can retrieve a maximum acupressure characteristic curve. The self-ignition prediction model 36 can search the ignition delay time f using the in-cylinder temperature, the finger pressure, the operating condition parameters, and the like as search keys. The knock determination value variation model 38 can search for kBMF using the operation conditions and the like as search keys. The combustion simulation program 40 can calculate an average acupressure characteristic curve by giving operating conditions, and has a function of calculating an in-cylinder temperature characteristic curve, a mass combustion ratio characteristic curve, and the like based on the acupressure characteristic curve. Stored.

  In order to obtain the optimal ignition timing, the CPU 12 advances the ignition timing little by little to acquire the operating conditions input from the advance angle processing unit 20 and the input unit 14 and execute the combustion simulation program. An average acupressure calculation part 22 for calculating an average acupressure characteristic curve, a maximum acupressure calculation part 24 for obtaining a maximum acupressure characteristic curve corresponding to the average acupressure characteristic curve using a cycle variation model, and combustion under conditions satisfying the maximum acupressure characteristic curve A mass combustion ratio / in-cylinder temperature calculation unit 26 that executes a simulation program to obtain a mass combustion ratio characteristic curve and an in-cylinder temperature characteristic curve, and an auto-ignition timing calculation part that calculates an auto-ignition timing tk using an auto-ignition prediction model 28. Knock presence / absence determination unit 30 for determining the presence / absence of knock using the knock determination value variation model, as long as the advance angle is repeated and knocking occurs Configured to include an optimal ignition timing setting unit 32 for setting the ignition timing of the as the optimum ignition timing. These functions can be realized by executing software, and specifically, can be realized by executing a corresponding optimum ignition timing setting program. Some of these functions may be realized by hardware.

  The operation of the optimum ignition timing setting device 10 having the above-described configuration, particularly the functions of the CPU 12, will be described in detail below according to the flowchart of FIG. 4 and the characteristic curves shown in FIGS. FIG. 4 is a flowchart showing a procedure for setting the optimum ignition timing, and each procedure corresponds to each processing procedure of the corresponding optimum ignition timing setting program.

After starting the optimal ignition timing setting device 10 and starting the optimal ignition timing setting program, the operating condition of the target internal combustion engine is input from the input unit 14. The operating conditions include the specifications of the internal combustion engine and the like, as well as the octane number of the fuel. Then, an initial value SA ₁ = SA ₀ of the ignition timing which is a starting point for obtaining the optimum ignition timing is given. Then, a combustion simulation is executed under the conditions, and an initial torque value τ ₁ = τ ₀ is calculated (S46, S48, S50).

This is shown in FIG. FIG. 5 shows the change in the torque τ when the ignition timing SA is changed by taking the ignition timing SA on the horizontal axis and the torque τ on the vertical axis. The torque becomes maximum at a certain ignition timing. It is shown. In this ignition timing-torque characteristic curve 50, knocking is less likely to occur as the ignition timing is set to the retard side than the timing indicating the maximum torque, and conversely, the ignition timing is set to the advance side toward the timing indicating the maximum torque. It is known that knocking is more likely to occur. Therefore, it is preferable to set the initial value of the ignition timing sufficiently on the retard side as the initial value for performing the calculation for setting the optimal ignition timing at the limit at which knocking occurs. In Figure 5, SA _1, as an initial value of the torque as the initial value of the ignition timing, torque tau ₁ is shown in SA _1. Note that TDC in FIG. 5 represents the ignition timing corresponding to the top dead center of the crank.

Then, by the function of the advance angle processing section 20 of the CPU 12, the initial value SA ₁ of the ignition timing is advanced by [Delta] SA (S52). This is shown by the arrow direction in FIG. Under the advanced condition, a combustion simulation is executed to obtain an average acupressure characteristic curve and a torque τ at the advanced ignition timing (S54). This function is executed by the average acupressure calculation unit 22 of the CPU 12. Specifically, the ignition timing is set to SA = SA ₁ + ΔSA under the operating conditions given in S 50, and the combustion simulation is executed using the combustion simulation program in the storage unit 18.

  An example of the average acupressure characteristic curve 52 obtained as a result of the combustion simulation is shown in FIG. The average acupressure characteristic curve 52 shows typical data of acupressure history under given driving conditions. As shown in FIG. 6, the average acupressure characteristic curve 52 is a characteristic curve in which the abscissa indicates the crank angle and the ordinate indicates the acupressure. The crank angle is defined as an angle from the top dead center (TDC) to 0 ° (After TDC; ATDC). If the rotational speed of the crank of the internal combustion engine is given, the crank angle directly corresponds to the time. As will be described later, since the ignition delay time f has a unit of time and 1 / f is integrated with respect to time, the crank angle indicating the mechanical angle is assumed to have a character as a time corresponding to this. deal with. That is, the time corresponding to the crank angle is used in this sense. Therefore, the ignition timing indicates time, but since this time can be easily converted into a crank angle, the ignition timing can also be indicated by a crank angle corresponding to that time.

When the average acupressure characteristic curve 52 is obtained, the torque τ at the ignition timing SA = SA ₁ + ΔSA is obtained and compared with the torque τ ₁ under the ignition timing SA ₁ (S56). 5 As described in, the ignition timing SA ₁ in step S50, the ignition timing - because it is set at a sufficiently retarded side than the ignition timing to be the maximum torque in the torque characteristic, if ΔSA is appropriate, after advancing The torque τ at the ignition timing is larger than the torque τ ₁ before advancement. Therefore, after the first advance, if normal, S56 is determined as YES, and the process proceeds to S58.

As will be described later, when the advance angle is repeated a plurality of times, the torque τ at the ignition timing after advance gradually approaches the maximum torque, eventually exceeds the maximum torque, and the torque τ at the ignition timing after advance advances. It becomes smaller than the torque τ ₁ before the corner. At this time, it is determined NO in S56, and the process proceeds to S74, where the ignition timing at the advance angle immediately before the last advance angle is set as the optimum ignition timing.

  If YES is determined in S56, the process proceeds to S58, and a cycle variation model corresponding to the condition of the average acupressure characteristic curve 52 is acquired. Then, the one with the highest acupressure among the plurality of acupressure characteristics curves of the acquired cycle variation model is specified as the acupressure characteristic with the highest possibility of knocking. That is, the maximum acupressure characteristic curve corresponding to the average acupressure characteristic curve 52 is specified (S60). This function is executed by the maximum acupressure calculation unit 24. Specifically, in the cycle variation model 34 of the storage unit 18, a cycle variation model corresponding to the average acupressure characteristic curve 52 calculated in S 54 is searched as a search key, and a plurality of acupressure characteristic curve data included therein is searched. Among them, the acupressure characteristic curve having the maximum acupressure is identified as the maximum acupressure characteristic curve with a high possibility of knocking. This is shown in FIG. FIG. 7 shows a plurality of acupressure characteristics curves belonging to the cycle variation model corresponding to the average acupressure characteristics curve 52, and among them, the one having the maximum torque is shown as the maximum acupressure characteristics curve 54.

  Subsequent processing is executed based on the maximum acupressure characteristic curve 54. As described above, by using the maximum acupressure characteristic curve 54 instead of the average acupressure characteristic curve 52, the fluctuation of the actual internal combustion engine operation state is reflected, and the occurrence of knocking occurs under the conditions where the knocking is most likely to occur. The limit ignition timing can be set as the optimum ignition timing. That is, it is possible to limit the evaluation of the occurrence of knocking to the limit, and accordingly, it is possible to increase the compression ratio of the internal combustion engine and set the ignition timing that can suppress knocking while improving the thermal efficiency.

  When the maximum acupressure characteristic curve 54 is calculated, a combustion simulation is executed so as to satisfy the condition, and a mass combustion ratio characteristic curve and an in-cylinder temperature characteristic curve are calculated (S62). The mass combustion ratio characteristic curve shows a change in the mass combustion ratio with the passage of time, and is specifically shown as a change in the mass combustion ratio with respect to the crank angle. A mass combustion ratio characteristic curve 70 is shown in FIG. 14 described later. The in-cylinder temperature characteristic curve shows a change with time of the in-cylinder temperature of the internal combustion engine, and is specifically shown as a change in the in-cylinder temperature with respect to the crank angle. An in-cylinder temperature characteristic curve 66 is shown in FIG.

  When the in-cylinder temperature characteristic curve is obtained, the pressure and temperature for each crank angle are obtained together with the maximum acupressure characteristic curve, so that the ignition delay time f can be obtained for each crank angle. Specifically, the following procedure is executed. That is, first, the f-1 / T characteristic is obtained (S64). Here, f is the ignition delay time as described above, and (1 / T) is the reciprocal of the in-cylinder temperature T. Since the f-1 / T characteristic is stored in the auto-ignition prediction model 36 of the storage unit 18 for each parameter related to actual driving conditions and driving conditions, the necessary f-1 / T characteristic is obtained using the parameter as a search key. Can be obtained by reading out.

  8 to 11 show examples of characteristics relating to the ignition delay time f stored in the self-ignition prediction model 36. FIG. 8 shows the f−1 / T characteristic 56 with the horizontal axis taking 1000 times 1 / T and the vertical axis taking f on a logarithmic scale. As shown in FIG. 8, in the f−1 / T characteristic 56, the change in the ignition delay time f with respect to the temperature T is less in the intermediate temperature region than in the temperature region before and after the intermediate temperature region. On the other hand, in the above-mentioned patent document 1, the ignition delay time f is simply treated as an exponential function of (1 / T), and such characteristic characteristics in the intermediate temperature region are not used. In FIG. 8, the finger pressure with respect to the ignition delay time f, that is, the effect of the pressure is shown by a characteristic curve 58. Here, it is shown that the ignition delay time f becomes shorter as the acupressure increases.

  FIG. 9 shows the effect of the equivalence ratio on the ignition delay time f by a characteristic curve 60. The method of taking the horizontal and vertical axes is the same as in FIG. Here, the equivalence ratio is a value defined by (theoretical air / fuel ratio / actual air / fuel ratio). In Patent Document 1, the effect of the equivalence ratio on the ignition delay time f is not shown. However, under an actual operating condition, the ignition delay time f varies depending on the equivalence ratio as shown in FIG. Here, it is shown that the ignition delay time f decreases as the equivalence ratio increases.

  FIG. 10 shows the effect of the fuel octane number on the ignition delay time f as a characteristic curve 62. The method of taking the horizontal and vertical axes is the same as in FIG. In Patent Document 1, although the effect of the octane number on the ignition delay time f is not shown, the ignition delay time f changes depending on the octane number under an actual driving condition as shown in FIG. Here, it is shown that the ignition delay time f increases as the octane number increases.

FIG. 11 shows the effect of the in-cylinder residual gas amount on the ignition delay time f as a characteristic curve 64. Here, the horizontal axis indicates the in-cylinder temperature T, and the vertical axis indicates f / f ₀ which is the ratio of the ignition delay time f to the ignition delay time f ₀ when the residual gas ratio is zero. . As shown in FIG. 11, the influence degree f / f ₀ of the residual gas amount has the maximum distribution characteristic at a certain in-cylinder temperature, and the influence degree f on the ignition delay time increases as the residual gas amount increases. / F ₀ increases.

  Using the data regarding the ignition delay time f, 1 / f is integrated over time from the time corresponding to the crank angle corresponding to the valve closing to the time corresponding to an arbitrary crank angle in the direction of the top dead center side ( In S66), the time when the time integral value becomes 1 or the crank angle corresponding to the time is set as the self-ignition timing tk (S68). This is a technique known as the Livengood-Wu integration as described above. This function is executed by the function of the self-ignition timing calculation unit 28.

  This is shown in FIGS. That is, FIG. 12 shows the in-cylinder temperature characteristic curve 66 obtained in S62, where the abscissa indicates the crank angle and the ordinate indicates 1/1000 of the in-cylinder temperature T. The maximum acupressure characteristic curve 54 calculated in S60 is also shown corresponding to the same horizontal axis. Using the temperature T at each crank angle of the in-cylinder temperature characteristic curve 66, the finger pressure at each crank angle of the maximum acupressure characteristic curve 54, the actual operating conditions, the equivalent ratio under the operating conditions, the octane number, and the residual gas amount, With reference to the characteristics of the ignition delay time f described with reference to FIGS. 8 to 11, the ignition delay time f at each crank angle under an actual driving condition is obtained. Each crank angle is converted into a corresponding time, and the reciprocal of the ignition delay time f is time-integrated. In the integration range, as described above, the time corresponding to the crank angle corresponding to the valve closing is the start point, and the time corresponding to the arbitrary crank angle in the direction toward the top dead center is the end point. FIG. 13 shows the state of the 1 / f time integration curve 68. The integration value increases as time integration is performed from the start point of the integration range toward the top dead center. Therefore, the time when the integral value becomes 1 is set as the self-ignition time tk (S68).

  Next, in the mass combustion ratio characteristic curve obtained in S62, pBMF that is a value corresponding to the self-ignition timing tk is obtained (S70). Then, according to the knock determination value variation model, it is compared with a predetermined knock generation mass combustion ratio kBMF to determine the presence or absence of knock (S72). This function is executed by the knock presence / absence determining unit 30. Specifically, the kBMF is read from the storage unit 18, the magnitude relationship with the pBMF obtained in S70 is determined, it is determined whether the pBMF is equal to or less than kBMF, and if the determination is YES, there is a knock, If it is NO, it means no knock.

  This is shown in FIG. FIG. 14 is a diagram showing the mass combustion ratio characteristic curve 70 obtained in S62, with the horizontal axis representing the crank angle and the vertical axis representing the mass combustion ratio BMF. The mass combustion ratio at the crank angle corresponding to the self-ignition timing tk is pBMF, and what is shown as kBMF in FIG. 14 is the knock generation mass combustion ratio. In the example of FIG. 14, since pBMF is larger than kBMF, the determination in S72 is NO.

If the determination in S72 is NO, knocking has not yet occurred at this ignition timing, so the function of the advance angle processing unit 20 returns to S52 again to advance the ignition timing by ΔSA, and further on and after S54. Follow the steps. In this manner, the ignition timing is successively advanced, so gradually knocking is likely to occur, with the advanced state of SA ₁ before the advanced state knocking is first generated and the optimum ignition timing SA ^* . Moreover, as explained in connection with S56, even if the tau is not determined to be greater than tau ₁ at S56, with the advanced state of SA ₁ before the advanced state, is the optimum ignition timing SA ^* (S74 ). This function is executed by the optimum ignition timing setting unit 32. In this way, the ignition timing is advanced little by little to determine whether or not knocking occurs using the ignition timing prediction method, and the optimum ignition timing can be determined by the limit ignition timing at which knocking occurs. .

  FIG. 15 summarizes the contents of FIG. 12, FIG. 13 and FIG. 14 in a single figure with the horizontal axis in common, and shows a state of comprehensive ignition timing optimization.

4 is a flowchart for explaining a principle flow of a method for obtaining an optimal ignition timing in the embodiment according to the present invention. In embodiment which concerns on this invention, it is a detailed internal flowchart of an ignition timing prediction method. In embodiment which concerns on this invention, it is a block diagram which shows the structure of the optimal ignition timing setting apparatus of a spark ignition internal combustion engine. 5 is a flowchart showing a procedure for setting an optimal ignition timing in the embodiment according to the present invention. In embodiment which concerns on this invention, it is a figure which shows an ignition timing-torque characteristic curve. In embodiment which concerns on this invention, it is a figure which shows the example of an average acupressure characteristic curve. In embodiment which concerns on this invention, it is a figure which shows the maximum acupressure characteristic curve corresponding to an average acupressure characteristic curve. In embodiment which concerns on this invention, it is a figure which shows the relationship between the ignition delay time f and the in-cylinder temperature T. FIG. In embodiment which concerns on this invention, it is a figure which shows the effect of the equivalence ratio with respect to the ignition delay time f. In embodiment which concerns on this invention, it is a figure which shows the effect of the fuel octane number with respect to the ignition delay time f. In embodiment which concerns on this invention, it is a figure which shows the effect of the cylinder residual gas amount with respect to the ignition delay time f. In embodiment which concerns on this invention, it is a figure which shows the example of a cylinder temperature characteristic curve. In the embodiment according to the present invention, it is a diagram showing the time integration of the reciprocal of the ignition delay time f and how the time when the integral value becomes 1 is set as the self-ignition timing tk. In embodiment which concerns on this invention, it is a figure explaining the relationship between the mass combustion ratio pBMF and the knock generation mass combustion ratio kBMF in self-ignition timing tk. In embodiment which concerns on this invention, it is a figure which shows the mode of a comprehensive ignition timing optimization.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 Optimal ignition timing setting apparatus, 12 CPU, 14 input part, 16 output part, 18 memory | storage part, 20 lead angle process part, 22 average acupressure calculation part, 24 maximum acupressure calculation part, 26 mass combustion ratio and in-cylinder temperature calculation part 28 auto ignition timing calculation unit, 30 knock presence / absence determination unit, 32 optimum ignition timing setting unit, 34 cycle fluctuation model, 36 auto ignition prediction model, 38 knock judgment value fluctuation model, 40 combustion simulation program, 50 ignition timing-torque characteristics Curve, 52 average acupressure characteristic curve, 54 maximum acupressure characteristic curve, 56 f-1 / T characteristic curve, 58, 60, 62, 64 characteristic curve showing effect on ignition delay time f, 66 in-cylinder temperature characteristic curve, 68 1 / F time integral curve, 70 mass combustion ratio characteristic curve.

Claims (7)

For a spark ignition type internal combustion engine, an ignition timing under an arbitrary operating condition is given, a combustion simulation is executed, and an average acupressure characteristic curve indicating a relationship of an average acupressure to a crank angle is calculated under the ignition timing, A step of obtaining a knock potential acupressure characteristic curve that may be knocked with respect to the calculated average acupressure characteristic curve;
Means for executing a combustion simulation under conditions satisfying the knock potential acupressure characteristic curve, and calculating a mass combustion ratio characteristic curve and an in-cylinder temperature characteristic curve with respect to a crank angle;
Based on the knock possibility acupressure characteristic curve and the in-cylinder temperature characteristic curve, obtaining a self-ignition timing according to a predetermined self-ignition prediction model using an ignition delay time that is a function of temperature and pressure;
A knock presence / absence determination step for determining a self-ignition mass combustion ratio, which is a mass combustion ratio corresponding to the self-ignition timing, from the mass combustion ratio characteristic curve, and determining the presence or absence of knock based on the obtained self-ignition mass combustion ratio;
An optimal ignition timing setting method for a spark ignition type internal combustion engine, characterized in that the ignition timing is changed and the ignition timing at the limit of occurrence of knocking is made the optimal ignition timing. In the spark ignition internal combustion engine optimal ignition timing setting method according to claim 1,
The process of calculating the knock potential acupressure characteristic curve is as follows:
Search the acupressure characteristics curve group under the cycle variation stored in advance for the average acupressure characteristics curve, identify the maximum acupressure characteristics curve showing the maximum acupressure characteristics among them, and knock this An optimum ignition timing setting method for a spark ignition type internal combustion engine. In the spark ignition internal combustion engine optimal ignition timing setting method according to claim 1,
The process for determining the auto-ignition time is
An optimal ignition timing setting method for a spark ignition type internal combustion engine, characterized in that an auto-ignition timing is obtained using an auto-ignition prediction model in which a change in ignition delay time with respect to temperature is smaller in an intermediate temperature region than in a temperature region before and after the intermediate temperature region. In the spark ignition internal combustion engine optimal ignition timing setting method according to claim 1,
The ignition delay time is determined as a function of at least one of the magnitude of the finger pressure, the in-cylinder temperature, the value of (theoretical air / fuel ratio / actual air / fuel ratio), the octane number, or the residual gas amount. An optimal ignition timing setting method for a spark ignition type internal combustion engine. In the spark ignition internal combustion engine optimal ignition timing setting method according to claim 1,
The knock presence determination process
An optimal ignition timing setting method for a spark ignition type internal combustion engine, characterized in that the presence or absence of knocking is determined by comparing the obtained self-ignition mass combustion ratio with a predetermined knock generation mass combustion ratio. For a spark ignition type internal combustion engine, a process of giving an ignition timing under an arbitrary operating condition and executing a combustion simulation, and giving an initial value of the ignition timing and torque;
Advancing the initial ignition timing, executing a combustion simulation, and calculating an average acupressure characteristic curve with respect to the torque and crank angle under the advance,
For the calculated average acupressure characteristic curve, search for a previously stored acupressure characteristic curve group under cycle fluctuations, and specify the maximum acupressure characteristic curve showing the maximum acupressure characteristic among them as the knocking potential acupressure characteristic curve And a process of
Executing a combustion simulation under conditions satisfying the knock possibility acupressure characteristic curve, calculating a mass combustion ratio characteristic curve with respect to the crank angle, and an in-cylinder temperature characteristic curve;
Based on the knock possibility acupressure characteristic curve and the in-cylinder temperature characteristic curve, obtaining a self-ignition timing according to a predetermined self-ignition prediction model using an ignition delay time that is a function of temperature and pressure;
Determine the mass combustion ratio corresponding to the auto-ignition timing from the mass combustion ratio characteristic curve, compare with a predetermined knock generation mass combustion ratio, and determine the presence or absence of knock generation,
If it is determined in the knock presence / absence determination step that knocking occurs, and if the torque obtained in the advance step is equal to or less than the torque before advance, the ignition timing before advance in the advance step is optimally ignited. An optimal ignition timing setting process for timing, and
In the knock presence / absence determination step, when it is not determined that knocking occurs, the optimal ignition timing setting for the spark ignition internal combustion engine is performed, returning to the advance step, further advancing, and repeating the subsequent steps. Method. An optimal ignition timing setting device for obtaining an optimal ignition timing of a spark ignition type internal combustion engine by a computer,
With respect to a spark ignition internal combustion engine, processing means for giving an ignition timing under an arbitrary operating condition to execute a combustion simulation and giving an initial value of the ignition timing and torque,
Advancing the initial ignition timing, executing a combustion simulation, and calculating an average acupressure characteristic curve with respect to the torque and crank angle under the advanced angle;
For the calculated average acupressure characteristic curve, search for a previously stored acupressure characteristic curve group under cycle fluctuations, and specify the maximum acupressure characteristic curve showing the maximum acupressure characteristic among them as the knocking potential acupressure characteristic curve Processing means to
Processing means for executing a combustion simulation under conditions satisfying the knock possibility acupressure characteristic curve, and calculating a mass combustion ratio characteristic curve with respect to a crank angle and an in-cylinder temperature characteristic curve;
A processing means for obtaining a self-ignition timing according to a predetermined self-ignition prediction model using an ignition delay time which is a function of temperature and pressure, based on a knock possibility acupressure characteristic curve and an in-cylinder temperature characteristic curve;
A knock presence determination processing means for determining a mass combustion ratio corresponding to the self-ignition timing from a mass combustion ratio characteristic curve, comparing with a predetermined knock generation mass combustion ratio, and determining whether knock has occurred,
If it is determined in the knock presence / absence determination step that knocking occurs, and if the torque obtained in the advance step is equal to or less than the torque before advance, the ignition timing before advance in the advance step is optimally ignited. Optimal ignition timing setting processing means for timing, and
In the knock presence / absence determining step, if it is not determined that knocking occurs, the optimal ignition timing setting of the spark ignition type internal combustion engine is performed by returning to the advance step, further advancing, and repeating the subsequent processes. apparatus.

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