JP2007248119A - Method for determining wiebe function parameter and device for presuming heat release rate of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a Wiebe function parameter determination method capable of modelizing heat release in the cylinders of an internal combustion engine with high accuracy, and a heat release rate presumption device for the internal combustion engine capable of presuming the in-cylinder heat release rate of the internal combustion engine with high accuracy. <P>SOLUTION: A real heat release rate at each crank angle is found, and a crank angle CAm at the maximum heat release rate being a crank angle at the point of time when the real heat release rate becomes the maximum is determined as one of Wiebe function parameters. Based on a real combustion rate α at the point of time when the real heat release rate becomes the maximum, the value of a shape parameter m is determined. Based on the crank angle CAm, the shape parameter m, etc., a crank angle CAs at a heat release start point of the Wiebe function is determined. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for determining a Wiebe function parameter and an apparatus for estimating a heat generation rate of an internal combustion engine, and in particular, uses a method for determining a Wiebe function parameter and a Wiebe function model for modeling heat generation in a cylinder of the internal combustion engine. The present invention relates to a heat generation rate estimation device for an internal combustion engine.

  Conventionally, attempts have been made to model heat generation in a cylinder of an internal combustion engine using a Wiebe function. According to the Wiebe function, it is possible to calculate a heat generation rate, a combustion rate, and the like for each crank angle. And if the value of the heat release rate for each crank angle is known, the in-cylinder pressure, the indicated torque, and the like can be calculated. Therefore, if the heat generation in the cylinder can be accurately modeled by the Wiebe function, the Wiebe function can be effectively used in the development stage of the internal combustion engine, the control device for the internal combustion engine, or the like.

  In order to accurately model the heat generation in the cylinder using the Wiebe function, it is necessary to accurately determine the values of some parameters included in the Wiebe function according to the model of the target internal combustion engine. The values of these parameters also vary depending on operating conditions such as air-fuel ratio, engine speed, load factor, and ignition timing.

  Japanese Patent Application Laid-Open No. 2004-332659 discloses a technique for controlling the ignition timing in the vicinity of MBT (Minimum advance for the Best Torque) using a Wiebe function. According to this publication, in the MBT of the same engine, the shape (waveform) of the heat generation rate is the same regardless of the length of the combustion period, and the crank angle and the combustion rate when the heat generation rate is maximized are also constant. It is assumed that Then, among the Wiebe function parameters, the shape parameter m related to the heat release rate shape is set as a constant, and these values are obtained by experiments (see paragraph number 0030 of the above publication). The parameter “n” in the above publication corresponds to “m” in this specification.

JP 2004-332659 A

  However, the above publication does not disclose any specific method for determining the shape parameter m and other Wiebe function parameters based on experimental data. Further, according to the knowledge of the present inventor, even in the MBT of the same engine, the value of the shape parameter m varies depending on operating conditions and is not constant. Further, in a modern engine in which various controls are performed, it is not always necessary to match the ignition timing with MBT. For this reason, there is also a request for estimating a torque or the like under an ignition timing other than MBT, and for that purpose, it is necessary to grasp the change tendency of the value of the Wiebe function parameter due to the change of the ignition timing.

  As described above, in order to effectively use the Wiebe function in the development of an internal combustion engine and the control device for the internal combustion engine, the Wiebe function parameters are accurately determined under various operating conditions, and those values are determined according to the operating conditions. It is necessary to know exactly how it will change. However, the actual situation is that a method for accurately determining the Wiebe function parameter has not been established.

  The present invention has been made to solve the above-described problems, and an object thereof is to provide a method for determining a Wiebe function parameter capable of accurately modeling heat generation in a cylinder of an internal combustion engine. . Another object of the present invention is to provide a heat generation rate estimation device for an internal combustion engine that can accurately estimate the heat generation rate in a cylinder of the internal combustion engine.

In order to achieve the above object, a first invention is a method for determining a Wiebe function parameter,
Obtaining an actual heat generation rate for each crank angle in the cylinder of the internal combustion engine;
Determining the maximum heat generation rate crank angle, which is the crank angle at the time when the actual heat generation rate is maximized, as one of the Wiebe function parameters;
Obtaining an actual combustion rate when the actual heat generation rate becomes maximum;
Determining a value of a shape parameter m which is one of the Wiebe function parameters based on the actual combustion rate;
With
The crank angle at the heat generation start point of the Wiebe function is defined as the value of the maximum heat release rate crank angle, the value of the shape parameter m, the value of the combustion period which is one of the Wiebe function parameters, and one of the Wiebe function parameters. The parameter a is set based on the value of the parameter a.

ＣＡｓ＝β×θ_ｐ−ＣＡｍ ・・・（III） The second invention is the first invention, wherein
In the step of determining the value of the shape parameter m, when the value of the actual combustion ratio is α, the value of the shape parameter m is determined by the following equation (I):
The maximum heat generation rate crank angle is represented by CAm [° ATDC], the crank angle at the heat generation start point of the Wiebe function is represented by CAs [° BTDC], the combustion period is represented by θ _p [°], and β is represented by the following formula (II): When the value is assumed, the following formula (III) is established.

CAs = β × θ _p −CAm (III)

The third invention is the first or second invention, wherein
An error indicating the magnitude of an error between the model heat generation rate for each crank angle calculated by the Wiebe function model using the determined maximum heat generation rate crank angle and the value of the shape parameter m and the actual heat generation rate The method further includes the step of determining values of the remaining Wiebe function parameters so that the evaluation value is minimized.

Moreover, 4th invention is set in 3rd invention,
The remaining Wiebe function parameters, characterized in that the is a combustion period theta _p, and efficiency k in which heat of the fuel supplied into the cylinder is converted into heat generation quantity in the cylinder.

The fifth invention is a heat release rate estimating device for an internal combustion engine,
Relationship storage means for storing the relationship between the operating condition of the internal combustion engine and the maximum heat generation rate crank angle, which is the crank angle at which the actual heat generation rate in the cylinder is maximum;
Based on the Wiebe function model, heat generation rate estimation means for calculating a model heat generation rate for each crank angle, which is an estimated value of the heat generation rate in the cylinder,
With
The heat generation rate estimation means is arranged so that the crank angle at which the model heat generation rate becomes maximum coincides with the maximum heat generation rate crank angle acquired according to operating conditions in accordance with the relationship stored in the relationship storage means. The model heat generation rate is calculated.

ＣＡｓ＝β×θ_ｐ−ＣＡｍ ・・・（Ｖ） The sixth invention is the fifth invention, wherein
The relationship storage means further stores the relationship between the operating conditions of the internal combustion engine, the shape parameter that is a Wiebe function parameter, and the combustion period,
The heat generation rate estimation means has a maximum heat generation rate crank angle acquired according to operating conditions in accordance with the relationship stored in the relationship storage means, CAm [° ATDC], a shape parameter m, and a combustion period θ _p [ °], where a which is one of the Wiebe function parameters is a predetermined constant, and β is a value represented by the following equation (IV), the crank angle CAs [° BTDC] of the heat generation start point of the Wiebe function is The model heat generation rate is calculated so as to be a value represented by equation (V).

CAs = β × θ _p −CAm (V)

  According to the first aspect of the present invention, when the heat generation in the cylinder of the internal combustion engine is modeled by the Wiebe function, the maximum heat generation rate crank that is the crank angle when the actual heat generation rate in the cylinder becomes the maximum. The angle can be determined as one of the Wiebe function parameters. According to the maximum heat release rate crank angle, the absolute crank angle of the heat generation start point (combustion start point) of the Wiebe function can be determined. The effect of operating conditions such as ignition timing is accurately reflected in the maximum heat release rate crank angle. Furthermore, since the maximum heat generation rate crank angle is uniquely determined by acquiring the actual heat generation rate for each crank angle, the value can be determined accurately and easily. According to the first invention, the shape parameter m can be determined with high accuracy by determining the value of the shape parameter m based on the actual combustion rate at the time when the actual heat generation rate becomes maximum. it can. For this reason, according to the first aspect of the present invention, it is possible to construct a highly accurate Wiebe function model that can accurately estimate the heat generation in the cylinder under all operating conditions.

  According to the second invention, the value of the shape parameter m can be determined with high accuracy and ease by using the above formula (I). Also, by using the above equations (II) and (III), the absolute crank angle CAs at the heat generation start point of the Wiebe function can be set with high accuracy and ease.

  According to the third aspect, the error between the model heat generation rate calculated by the Wiebe function model using the determined maximum heat generation rate crank angle and the value of the shape parameter m and the actual heat generation rate is minimized. As described above, the values of the remaining Wiebe function parameters can be determined with high accuracy.

According to the fourth invention, as the remaining Wiebe function parameters, the values of the combustion period theta _p and efficiency k can be accurately determined.

  According to the fifth aspect of the present invention, in estimating the heat generation rate in the cylinder of the internal combustion engine using the Wiebe function model, the heat generation that is the crank angle at the time when the actual heat generation rate in the cylinder becomes the maximum. The rate maximum crank angle can be used as one of the Wiebe function parameters. That is, the heat generation rate is estimated so that the crank angle at which the estimated value of the heat generation rate becomes the maximum coincides with the maximum heat generation rate crank angle acquired according to the operation condition based on the relationship stored in advance. be able to. The effect of operating conditions such as ignition timing is accurately reflected in the maximum heat release rate crank angle. Therefore, according to the fifth aspect of the invention, the heat generation rate under various operating conditions can be accurately estimated by using the maximum heat generation rate crank angle as the Wiebe function parameter.

  According to the sixth aspect, in estimating the heat generation rate for each crank angle, the crank angle at the heat generation start point can be accurately calculated based on the maximum heat generation rate crank angle.

Embodiment 1 FIG.
[Description of system configuration]
FIG. 1 is a diagram for explaining a system configuration used in Embodiment 1 of the present invention. As shown in FIG. 1, the system of this embodiment includes a spark ignition type internal combustion engine 10. Each cylinder of the internal combustion engine 10 is provided with an intake valve 14, an exhaust valve 16 and a spark plug 30.

  The internal combustion engine 10 is provided with a crank angle sensor 12 that detects the rotational position (crank angle) of the crankshaft. The crank angle sensor 12 is a sensor that reverses the Hi output and the Lo output each time the crankshaft rotates by a predetermined rotation angle. According to the output of the crank angle sensor 12, the engine speed NE can also be detected.

  The internal combustion engine 10 incorporates an in-cylinder pressure sensor 18. The in-cylinder pressure sensor 18 can detect the pressure generated in the cylinder (combustion chamber).

  A surge tank 20 is provided in the intake passage 19 of the internal combustion engine 10. The surge tank 20 is provided with an intake pressure sensor 21 for detecting the internal pressure, that is, the intake pipe pressure. In addition, an air flow meter 22 that detects an intake air amount GA flowing through the inside of the intake passage 19 is disposed. According to the output of the intake pressure sensor 21, the load factor KL [%] of the internal combustion engine 10 can be acquired. The load factor KL may be calculated based on the intake air amount GA and the engine speed NE.

  A throttle valve 24 is disposed downstream of the air flow meter 22. In the vicinity of the throttle valve 24, a throttle opening sensor 26 for detecting the throttle opening TA is assembled.

  An injector 28 for injecting fuel such as gasoline is disposed at the intake port of the internal combustion engine 10. The internal combustion engine in the present invention is not limited to such a port injection type internal combustion engine, but is an in-cylinder direct injection type internal combustion engine or an internal combustion engine that uses both port injection and in-cylinder injection. May be.

  An air-fuel ratio sensor 33 for detecting the air-fuel ratio of the exhaust gas is installed in the exhaust passage 32 of the internal combustion engine 10. A catalyst 34 for purifying exhaust gas is incorporated in the exhaust passage 32.

  The system of this embodiment includes an ECU (Electronic Control Unit) 50 as a control device. Sensor signals are supplied to the ECU 50 from the various sensors described above. The ECU 50 can control various actuators such as the throttle valve 24, the injector 28, and the spark plug 30 based on those sensor signals. In addition, as will be described later, the ECU 50 can perform Wiebe function parameter determination processing based on sensor signals from the crank angle sensor 12, the in-cylinder pressure sensor 18, and the like. Furthermore, the ECU 50 can perform a process of estimating a heat generation rate due to combustion in the cylinder based on a Wiebe function model stored in advance.

(Wiebe function)
The Wiebe function of the present embodiment is expressed by the following formula (1) or the following formula (2).

The meaning of each symbol in the above formulas (1) and (2) is as follows.
Q: Calorific value in the cylinder of the internal combustion engine 10 [J]
Q _total : calorific value of fuel supplied to the cylinder [J]
θ: Crank angle relative to the heat generation start point [°]
θ _p : Combustion period [°]
m: shape parameter k: efficiency

The above equation (1) is a Wiebe function for calculating the heat release rate dQ / dθ in the cylinder of the internal combustion engine 10. Q / kQ _{total on} the left side of the equation (2) represents a combustion ratio in the cylinder of the internal combustion engine 10 as described later. That is, the above equation (2) is a Wiebe function for calculating the combustion ratio Q / kQ _total .

  FIG. 2 is a graph in which the horizontal axis represents the crank angle and the vertical axis represents the heat generation rate dQ / dθ. According to the Wiebe function of the above equation (1), the heat generation rate dQ / dθ for each crank angle can be calculated. In the following description, the heat generation rate dQ / dθ calculated based on this Wiebe function is referred to as “model heat generation rate”. The thick solid line in FIG. 2 represents the model heat generation rate.

  On the other hand, in the system shown in FIG. 1, the in-cylinder pressure can be measured for each crank angle by the in-cylinder pressure sensor 18. In the following description, the measured value by the in-cylinder pressure sensor 18 is referred to as “actual in-cylinder pressure”. As will be described later, the heat release rate for each crank angle can be calculated from the actual in-cylinder pressure using an energy conservation law equation. In the following description, the heat generation rate calculated based on the actual in-cylinder pressure is referred to as “actual heat generation rate”. A thick broken line in FIG. 2 represents an actual heat generation rate.

  In the present specification, when “every crank angle” is referred to, the interval between the crank angles is not particularly limited, and can be, for example, about 1 °.

  According to the Wiebe function of the above equation (1), when θ = 0, the model heat generation rate dQ / dθ = 0 is calculated. Then, when θ exceeds 0, dQ / dθ> 0, which means that heat generation starts. That is, in the Wiebe function of the above equation (1), θ = 0 is the heat generation start point (combustion start point), and thus θ is the crank angle (after the heat generation start is based on the heat generation start point) as described above. The elapsed crank angle).

  In the present specification, a plurality of parameters whose values need to be determined in calculating the model heat generation rate for each crank angle by the Wiebe function are referred to as “Wiebe function parameters”. In accurately modeling the heat generation in the cylinder of the actual machine (internal combustion engine 10) using the Wiebe function, each Wiebe function is set so that the error between the actual heat generation rate and the model heat generation rate is as small as possible. It is necessary to determine the parameter value with high accuracy. Hereinafter, each parameter of the Wiebe function will be described sequentially.

(Combustion period θ _p )
As shown in FIG. 2, the combustion period θ _p is a period during which heat generation by combustion continues, that is, a period from the heat generation start point (combustion start point) to the heat generation end point (combustion end point) in terms of the crank angle. It has a physical meaning as expressed. Wiebe function, since the heat generation is to model the state continues, domain becomes 0 ≦ θ ≦ θ _p that.

(Shape parameter m)
The shape parameter m is a parameter greatly related to the shape of the model heat generation rate in the graph as shown in FIG. 2, and is particularly a parameter greatly related to the crank angle at which the model heat generation rate takes the maximum value.

(Efficiency k)
In the above formulas (1) and (2), the heat quantity Q _total of the fuel supplied into the cylinder can be calculated by multiplying the fuel quantity supplied into the cylinder by the lower heating value of the fuel. The lower heating value is a physical property value called a true heating value. The lower calorific value is the amount of heat generated when a unit amount of fuel is completely burned, minus the amount of heat (latent heat) required to evaporate the moisture contained in the fuel and the moisture generated by the combustion. means.

Combustion in an internal combustion engine usually involves some heat loss due to a cooling loss, unburned fuel, and the like. For this reason, it is practically impossible for all the amount of heat Q _{total of} the fuel supplied into the cylinder to be directly converted into the amount of heat generated Q in the cylinder. In this embodiment, efficiency k is introduced as a parameter for reflecting this in the Wiebe function. That is, the efficiency k has a physical meaning as an efficiency in which the heat quantity Q _{total of} the fuel supplied into the cylinder is converted into the heat generation quantity Q, and is a number in a range of 0 <k <1.

When the efficiency k is used, the total calorific value in the cylinder can be expressed as kQ _total obtained by multiplying Q _total by k. The total calorific value kQ _total is represented by an area surrounded by a curve of the heat generation rate dQ / dθ and a straight line of dQ / dθ = 0 in the graph as shown in FIG. The value of the total calorific value kQ _total in the actual machine can be calculated by integrating the actual heat generation rate.

Since the total calorific value is expressed as kQ _total as described above, the combustion ratio at a certain crank angle θ is expressed as a ratio Q / kQ _total between the calorific value Q up to the crank angle θ and the total calorific value kQ _total. be able to. This combustion ratio Q / kQ _total is expressed by the above equation (2) according to the Wiebe function. When the equation (2) is differentiated by θ, the equation (1) is obtained. That is, the above equation (2) is equivalent to the above equation (1).

(Parameter a)
From original definition of combustion rate, the value of the combustion rate is at combustion end, it should be 1 (100%) in other words θ = θ _p. On the other hand, the Wiebe function, the combustion rate at the combustion end, by substituting theta = theta _p in equation (2) is represented by the following formula.
Q / kQ _total (at the end of combustion) = 1−exp (−a) (3)

As shown in the above equation (3), the value of the combustion ratio Q / kQ _total at the end of combustion calculated by the Wiebe function is a function of only the parameter a. This value is smaller than “1” by “−exp (−a)” and cannot be “1”. Therefore, in this embodiment, it is assumed that the combustion ratio at the end of combustion calculated by the Wiebe function is a value close to 1 (here, 0.999). According to this assumption, the following equation is obtained.
Q / kQ _total (at the end of combustion) = 1−exp (−a) = 0.999 (4)
When equation (4) is solved as an equation, a≈6.9. Therefore, in this embodiment, the parameter a is handled as a constant 6.9.

As described above, the four combustion parameters θ _p , the shape parameter m, the efficiency k, and the parameter a have been described as the Wiebe function parameters. In calculating the model heat generation rate for each crank angle by the Wiebe function, it is necessary to set another Wiebe function parameter for the following reason. As described above, the crank angle θ in the Wiebe function of the above equation (1) is based on the heat generation start point of the Wiebe function. For this reason, in order to calculate the model heat generation rate for each crank angle, the Wiebe function parameter for determining the relationship between the crank angle θ of the Wiebe function and the absolute crank angle (for example, the top dead center reference crank angle). Need more. As such a Wiebe function parameter, for example, an ignition delay θ _b can be assumed.

After the air-fuel mixture in the cylinder is ignited by the spark plug 30, there is a slight delay until combustion starts and the actual heat generation rate rises. For this reason, as shown in FIG. 2, in order to accurately match the waveform of the model heat generation rate by the Wiebe function with the waveform of the actual heat generation rate, the heat generation start point of the Wiebe function is delayed from the ignition timing SA. Must be in position. The ignition delay θ _b is a parameter for meeting this requirement, and is defined as a value representing the delay from the ignition timing SA of the heat generation start point of the Wiebe function with a crank angle.

By adding the ignition delay theta _b as a Wiebe function parameters, it is possible to determine the absolute crank angle of the heat generation starting point of the Wiebe function, it is possible to calculate the model heat release rate for each crank angle . However, as shown in FIG. 2, the actual heat generation rate tends to have a gentle shape at the rising portion, whereas the model heat generation rate tends to have a shape that rises at a stretch from the heat generation start point. For this reason, the actual heat generation rate and the model heat generation rate may not coincide with each other immediately after the start of heat generation. In such a case, can not be determined uniquely the value of ignition delay theta _b, it will likely be difficult to accurately determine the ignition delay theta _b. For this reason, if the ignition delay θ _b is used as the Wiebe function parameter, it is difficult to determine the value of the ignition delay θ _b with sufficient accuracy, and as a result, accurate modeling is likely to be difficult.

Therefore, in the present embodiment, the ignition delay θ _b is not used as the Wiebe function parameter, but instead, the crank angle at the time when the actual heat generation rate becomes maximum (hereinafter referred to as “the maximum heat generation rate crank angle”). ")" Was used as the Wiebe function parameter. In the following description, the maximum heat release rate crank angle is expressed as a crank angle with reference to the compression top dead center, and the symbol is expressed as CAm [° ATDC].

The maximum heat generation rate crank angle CAm is a crank angle when the actual heat generation rate reaches its peak, and can be easily determined uniquely from the waveform of the actual heat generation rate. For this reason, if the maximum heat release rate crank angle CAm is used as the Wiebe function parameter, the value can be easily determined with high accuracy. Further, as will be described later, if the maximum heat generation rate crank angle CAm is used, the heat generation start point and end point of the Wiebe function can be determined without using the ignition delay θ _b , so that a model for each crank angle is used. It becomes possible to calculate a heat release rate.

[Wiebe Function Parameter Determination Method in Embodiment 1]
Hereinafter, specific processing in the first embodiment will be described. FIG. 3 is a flowchart of a routine executed by the ECU 50 in the present embodiment in order to determine the value of the Wiebe function parameter based on the actual machine data.

According to the routine shown in FIG. 3, first, during operation of the internal combustion engine 10, the actual in-cylinder pressure P _data [Pa] for each crank angle is measured based on the outputs of the crank angle sensor 12 and the in-cylinder pressure sensor 18. (Step 100). In step 100, the measurement of the actual in-cylinder pressure P _data may not be performed over the entire crank angle range, and may be performed within a range including at least the actual combustion period.

Next, the actual heat generation rate for each crank angle is calculated by the following method based on the actual in-cylinder pressure P _data for each crank angle measured in step 100 (step 102). The following equation is an equation representing a thermodynamic energy conservation law using the heat generation rate dQ / dθ, the in-cylinder pressure P, the in-cylinder volume V [m ³ ], and the crank angle θ. The crank angle θ in the following equation represents an absolute crank angle based on the top dead center, unlike θ in the Wiebe function such as the above equation (1).

In the above equation (5), κ is a specific heat ratio, which is a known value determined based on the composition of the combustion gas. The in-cylinder volume V and the rate of change dV / dθ are geometrically determined values according to the crank angle θ. Therefore, by substituting these known values and the value of the actual in-cylinder pressure P _data for each crank angle measured in the above step 100 into the above equation (5), as shown by the thick broken line in FIG. The actual heat generation rate dQ / dθ for each crank angle can be calculated.

  In calculating the actual heat generation rate in step 102, for example, temperature information such as the cooling water temperature of the internal combustion engine 10, information on exhaust gas components, and the like are taken into account, and correction is performed based on the information. May be.

  Subsequently, the maximum value of the actual heat generation rates for each crank angle calculated in step 102 is searched. Then, the value of the crank angle at the time when the actual heat generation rate takes the maximum value is acquired, and the value is determined as the heat generation rate maximum crank angle CAm (step 104).

Next, the total calorific value kQ _total is calculated based on the actual heat generation rate for each crank angle calculated in step 102 (step 106). Specifically, the total heat generation amount kQ _total is calculated by integrating (integrating) the actual heat generation rate for each crank angle calculated in step 102.

Subsequently, the combustion rate at the time when the actual heat generation rate becomes maximum, that is, the combustion rate at the maximum heat generation rate crank angle CAm is calculated (step 108). In the following description, the combustion ratio at the maximum heat release rate crank angle CAm is referred to as “actual combustion ratio”, and the value is represented by the symbol α. Specifically, in step 108, first, the actual heat generation rate for each crank angle calculated in step 102 is integrated (integrated) up to the maximum heat generation rate crank angle CAm, whereby the maximum heat generation rate crank is obtained. A value of the heat generation amount up to the angle CAm is calculated, and then a value obtained by dividing the value by the total heat generation amount kQ _total calculated in step 106 is calculated as the actual combustion ratio α.

  Next, a process for determining the value of the shape parameter m is performed using the value of the actual combustion ratio α calculated in step 108 (step 110). This process is performed based on the concept described below.

  The value on the Wiebe function corresponding to the actual combustion rate α, that is, the value of the combustion rate when the model heat generation rate is maximized, is the model heat generation rate in the area surrounded by the model heat generation rate graph of FIG. 2 can be calculated as a value obtained by dividing the area up to the crank angle where hatching is maximum (hatched portion in FIG. 2) by the total area.

In order to calculate this value, first, the above formula (1) is differentiated by θ, and d ² Q / dθ ² = 0, so that the crank angle θ _{* at} which the model heat generation rate dQ / dθ is maximized is obtained. Ask. By performing the following expression expansion, an expression representing the crank angle θ _* is obtained.

By substituting the crank angle θ _* represented by the above equation (6) into the above equation (2), the combustion rate at the crank angle θ _* at which the model heat generation rate dQ / dθ is maximized is expressed by the following (7) It can be expressed by a formula.

As shown in the above equation (7), the value of the combustion ratio at the crank angle θ _* at which the model heat generation rate dQ / dθ is maximum is expressed as a function of only the shape parameter m. Solving this value, that is, the right side of the above equation (7) and the actual combustion rate α corresponding to the actual machine data, with respect to m, the following equation (8) is obtained.

  In step 110, based on the concept described above, a value calculated by substituting the value of the actual combustion ratio α calculated in step 108 into the above equation (8) is determined as the value of the shape parameter m. The

  By the way, in the present embodiment, when the value of the shape parameter m is determined as described above, the heat generation start point (combustion start point) and the heat generation end point (combustion end) of the Wiebe function are described as described below. It is possible to determine the absolute crank angle of point). Below, the absolute crank angle of the heat generation start point of the Wiebe function with reference to the compression top dead center is represented by the symbol CAs [° BTDC]. Similarly, the absolute crank angle of the end point of heat generation of the Wiebe function with reference to the compression top dead center is represented by the symbol CAe [° ATDC].

First, the (6) the value of the both sides divided by combustion period theta _p of formula is denoted by beta. That is, β is defined by the following formula.

As indicated by the above equation (9), β is represented only by the parameter a and the shape parameter m. In the present embodiment, as described above, it is assumed that a = 6.9. Further, the value of the shape parameter m is determined by the processing of step 110 described above. Therefore, the value of β can be treated as a value that has been determined by the processing so far. From the above equation (9), the following equation is established.
θ _* = β × θ _p (10)

Further, as shown in FIG. 2, the crank angle theta _* to model heat generation rate is the maximum, placing the time to heat generation and the end point theta _res, the definition and equation (10) of the theta _res, following The formula holds.
θ _res = θ _p −θ _* = (1−β) × θ _p (11)

In the present embodiment, the Wiebe function parameter is determined so that the maximum heat generation rate crank angle CAm at which the actual heat generation rate is maximum matches the crank angle θ _{* at} which the model heat generation rate is maximum. When the maximum heat generation rate crank angle CAm based on the compression top dead center is made to coincide with the crank angle θ _* based on the heat generation start point, CAm, θ _* , θ _res , the heat generation start point CAs, and the heat generation end The relationship shown in FIG. 2 is established between the points CAe. From this relationship and the above equations (10) and (11), the following equation can be derived.
CAs = θ _* −CAm = β × θ _p −CAm (12)
CAe = CAm + θ _res = CAm + (1−β) × θ _p (13)

As shown in the above equations (12) and (13), the absolute crank angles CAs and CAe at the combustion start point and the combustion end point of the Wiebe function are the heat release rate maximum crank angle CAm, the combustion period θ _p , It can be represented by β, which is a determined value. Thus, if the heat release rate maximum crank angle CAm is used as the Wiebe function parameter, the heat generation start point CAs of the Wiebe function can be determined. Therefore, without using the ignition delay theta _b, it is possible to calculate the model heat release rate for each crank angle by Wiebe function of equation (1).

It should be noted that, by definition, is a CAs + CAe = θ _p. According to this relationship, the above equations (12) and (13) are equivalent to each other.

By the processing so far, the maximum heat release rate crank angle CAm and the shape parameter m are determined as the Wiebe function parameters. The remaining Wiebe function parameters to be determined are efficiency k and combustion period θ _p . In the present embodiment, subsequent to the processing in step 110, processing for determining the values of the efficiency k and the combustion period θ _p by the least square method is performed (step 112).

Specifically, first, the equation (1) assigns the value of the temporary efficiency k and combustion duration theta _p of Wiebe functions, determination of the the parameter a, the maximum heat generation rate crank angle CAm and shape parameter m The model heat generation rate for each crank angle is calculated using the completed values. Next, the square of the error (deviation) between the model heat generation rate for each crank angle and the actual heat generation rate for each crank angle (calculated in step 102 above) is calculated from the heat generation start point CAs to the heat generation end point. A value (sum of squared errors) obtained by adding up to CAe is calculated. The calculation of the error sum of squares, while changing the value of the temporary efficiency k and combustion period theta _p, is repeated. The combination of the temporary value of efficiency k and combustion duration theta _p that minimizes the error sum of squares is determined as the final value of the efficiency k and combustion duration theta _p. According to this process, as the error between the actual heat release rate and the model heat generation rate is minimized, it is possible to determine the value of the efficiency k and combustion duration theta _p.

As described above, in the present embodiment, instead of the ignition delay theta _b, the heat generation rate up crank angle CAm was decided to use as a Wiebe function parameters. Maximum crank angle CAm heat generation rate, because it is easy to uniquely determined from the waveform of the actual heat release rate, than the ignition delay theta _b, it is possible to determine the value with high precision. For this reason, according to the above-described method, a Wiebe function model for modeling heat generation in the cylinder of the internal combustion engine 10 can be constructed with high accuracy and easily.

  Further, according to the knowledge of the present inventor, the maximum heat release rate crank angle CAm has a property of continuously advancing as the ignition timing SA is advanced (as it approaches MBT). That is, it can be said that the influence of the operating conditions of the internal combustion engine 10, particularly the influence of the ignition timing SA is accurately reflected in the maximum heat release rate crank angle CAm. For this reason, it can be said that it is reasonable to set the maximum heat release rate crank angle CAm as a Wiebe function parameter, and it works advantageously in constructing a highly accurate Wiebe function model.

  Further, in the present embodiment, the value of the shape parameter m can be directly determined only from the value of the actual combustion ratio α by the processing of step 110 described above. According to the knowledge of the present inventor, the actual combustion rate α at the time when the actual heat generation rate becomes the maximum changes continuously with respect to the change of the ignition timing SA, similarly to the maximum heat generation rate crank angle CAm. To do. That is, it can be said that the value of the actual combustion ratio α accurately reflects the influence of the operating condition of the internal combustion engine 10, particularly the influence of the ignition timing SA. For this reason, it can be said that it is reasonable to determine the value of the shape parameter m from the actual combustion ratio α as in the present embodiment, and it works advantageously in constructing a highly accurate Wiebe function model.

Note that, in step 112 of the routine shown in FIG. 3 has determined the values of efficiency k and combustion duration theta _p by the least squares method to the error sum of squares as the error evaluation value, a minimum non-squares optimization methods You may make it determine those values by. In the present invention, the efficiency values k and combustion duration theta _p is may be determined by the optimization technique than techniques such as in step 112. For example, the calorific value Q _{total of} the fuel supplied into the cylinder is calculated based on the lower calorific value of the fuel, the fuel injection quantity from the injector 28, etc., and the total calorific value kQ _total calculated in step 106 is calculated as The value of efficiency k may be determined by dividing by _Qtotal .

[Heat generation rate estimating apparatus for internal combustion engine in Embodiment 1]
The values of the Wiebe function parameters determined by the routine processing shown in FIG. 3 are the operating conditions of the internal combustion engine 10 (in this embodiment, the ignition timing SA, the engine speed NE, the air-fuel ratio A / F, and the load factor KL). 4). Therefore, the ignition timing SA, the engine speed NE, the air-fuel ratio A / F, and the load factor KL are respectively changed, and the routine shown in FIG. 3 is performed under each operating condition to collect and analyze the data. The relationship between each Wiebe function parameter and the operating condition of the internal combustion engine 10 can be grasped.

The relations ascertained in this way can be summarized in an arithmetic expression such as a function or a map. Here, the heat generation rate up crank angle CAm, the shape parameter m, the relationship between each and the operating conditions of efficiency k and combustion duration theta _p is, the ignition timing SA, engine speed NE, the air-fuel ratio A / F and the load factor KL Are summarized as the following functions f _{1 to} f ₄ .
CAm = f ₁ (SA, NE, A / F, KL)
m = f ₂ (SA, NE, A / F, KL)
k = f ₃ (SA, NE, A / F, KL)
θ _p = f ₄ (SA, NE, A / F, KL)

If a relationship such as the above functions f _{1 to} f ₄ is stored in the ECU 50, a heat generation rate estimation device capable of calculating the model heat generation rate for each crank angle based on the Wiebe function model for all operating conditions is configured. can do.

FIG. 4 is a flowchart of a routine executed by the ECU 50 in order to calculate a model heat generation rate that is an estimated value of the heat generation rate in the heat generation rate estimation device configured as described above. According to the routine shown in FIG. 4, first, the values of the ignition timing SA, engine speed NE, air-fuel ratio A / F, and load factor KL, which are the operating conditions for which the heat generation rate is to be estimated, are stored in the ECU 50. by substituting into the function f ₁ ~f _4, the heat generation rate up crank angle CAm corresponding to the operating condition, the shape parameter m, each value of efficiency k and combustion duration theta _p is obtained (step 120).

Subsequently, the crank angle CAs of the heat generation start point of the Wiebe function is calculated (step 122). Specifically, first, based on the value of the shape parameter m acquired in step 120, a is calculated as a = 6.9 according to the above equation (9). Then, the value of this beta, based on the value of the maximum crank angle CAm obtained heat release rate and combustion duration theta _p in step 120, according to the above (12), a crank angle CAs of the heat generation starting point is calculated The

Then, by using the values acquired in steps 120 and 122, a model heat generation rate for each crank angle is calculated as an estimated value of the heat generation rate (step 124). Specifically, the shape parameter m calculated in step 120, the value of efficiency k and combustion period theta _p substituted into equation (1), the crank angle of the heat generation starting point is calculated in step 122 The model heat generation rate for each crank angle is calculated so as to be CAs. Since the above expression (12) and the above expression (13) are equivalent, if the end point of heat generation is set to CAs, the end point of heat generation inevitably coincides with CAe in the above expression (13).

Further, in the process of step 124, by setting the heat generation start point of the model heat generation rate as CAs, the relationship shown in FIG. 2 is established among CAm, θ _* , and CAs. For this reason, the crank angle θ _* at which the model heat generation rate calculated in step 124 is maximum matches the heat generation rate maximum crank angle CAm acquired in step 120. Therefore, according to the routine processing shown in FIG. 4, the crank angle at which the estimated heat generation rate is maximized can always be matched with the tendency obtained from the actual machine data regardless of the operation condition to be estimated. it can. Therefore, the heat generation rate in the cylinder can be accurately estimated with respect to all operating conditions.

  By the way, if the estimated value of the heat release rate for each crank angle is obtained, the estimated value of the in-cylinder pressure for each crank angle can be calculated by combining this with the energy conservation law of the above equation (5). Further, the indicated torque of the internal combustion engine 10 can be calculated from the value of the in-cylinder pressure for each crank angle. According to the present invention, since the heat generation rate can be accurately estimated by the routine processing shown in FIG. 4, the in-cylinder pressure and torque under all operating conditions can be calculated using the estimated heat generation rate. It is possible to estimate with high accuracy.

  The estimation results of the in-cylinder pressure and torque of the internal combustion engine 10 obtained as described above can be effectively used at the development stage of the internal combustion engine 10 or the like. That is, conventionally, when the control logic is examined at the development stage of the internal combustion engine 10, it is necessary to actually measure the in-cylinder pressure, torque, and the like under various operating conditions. On the other hand, according to the present invention, it is possible to accurately grasp the relationship between the value of the Wiebe function parameter and the operating condition and construct a highly accurate Wiebe function model. If the above-described heat generation rate estimation device that stores the Wiebe function model is used, it is possible to replace the actual measurement work of the in-cylinder pressure and torque with prediction based on the Wiebe function model. For this reason, the number of measurement points of actual machine data can be greatly reduced, and the development man-hours and development costs can be greatly reduced.

  Such a Wiebe function model can also be stored in the in-vehicle ECU. If the Wiebe function model is stored in the in-vehicle ECU, the in-cylinder pressure and torque under various operating conditions can be accurately predicted for the internal combustion engine 10 mounted on the vehicle. If the prediction result is used, the vehicle-mounted ECU can accurately perform various controls such as torque demand control and drivability improvement control.

  It is also possible to cause the in-vehicle ECU to execute a routine for determining the Wiebe function parameter shown in FIG. If the Wiebe function parameter is calculated (determined) by executing the routine shown in FIG. 3 in the in-vehicle ECU, and the value of the calculated Wiebe function parameter is learned in relation to the current operating state, the in-vehicle ECU It is possible to modify the Wiebe function model stored in (1) according to the current state of the internal combustion engine 10. That is, the Wiebe function model stored in the in-vehicle ECU can be modified with higher accuracy by reflecting the change with time in the characteristics of the internal combustion engine 10 and individual differences.

  In the above description, various formulas as described above are used. However, in the present invention, these formulas need not be completely the same as those described above, and formulas equivalent to them may be used. Good.

  In the first embodiment described above, the ECU 50 corresponds to the “relation storage means” in the fourth and fifth inventions. Further, the “heat generation rate estimating means” in the fourth and fifth inventions is realized by the ECU 50 executing the processing of the routine shown in FIG.

It is a figure for demonstrating the system configuration | structure of Embodiment 1 of this invention. It is a graph in which the horizontal axis represents the crank angle and the vertical axis represents the heat generation rate dQ / dθ. It is a flowchart of the routine performed in Embodiment 1 of the present invention. It is a flowchart of the routine performed in Embodiment 1 of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Internal combustion engine 12 Crank angle sensor 14 Intake valve 16 Exhaust valve 18 In-cylinder pressure sensor 21 Intake pressure sensor 30 Spark plug 33 Air-fuel ratio sensor 34 Catalyst 50 ECU (Electronic Control Unit)

Claims (6)

A method for determining the value of a parameter of a Wiebe function for modeling heat generation due to combustion in a cylinder of an internal combustion engine,
Obtaining an actual heat generation rate for each crank angle in the cylinder of the internal combustion engine;
Determining the maximum heat generation rate crank angle, which is the crank angle at the time when the actual heat generation rate is maximized, as one of the Wiebe function parameters;
Obtaining an actual combustion rate when the actual heat generation rate becomes maximum;
Determining a value of a shape parameter m which is one of the Wiebe function parameters based on the actual combustion rate;
With
The crank angle at the heat generation start point of the Wiebe function is defined as the value of the maximum heat release rate crank angle, the value of the shape parameter m, the value of the combustion period which is one of the Wiebe function parameters, and one of the Wiebe function parameters. A method for determining a Wiebe function parameter, wherein the parameter is set based on a value of a parameter a. In the step of determining the value of the shape parameter m, when the value of the actual combustion ratio is α, the value of the shape parameter m is determined by the following equation (I):
The maximum heat generation rate crank angle is CAm [° ATDC], the heat generation start crank angle of the Wiebe function is CAs [° BTDC], the combustion period is θ _p [°], and β is expressed by the following formula (II): 2. The method for determining a Wiebe function parameter according to claim 1, wherein the following equation (III) holds:

CAs = β × θ _p −CAm (III)   An error indicating the magnitude of an error between the model heat generation rate for each crank angle calculated by the Wiebe function model using the determined maximum heat generation rate crank angle and the value of the shape parameter m and the actual heat generation rate The method of determining a Wiebe function parameter according to claim 1 or 2, further comprising a step of determining values of the remaining Wiebe function parameters so that the evaluation value is minimized. The remaining Wiebe function parameters, the combustion period theta _p, claim 3, wherein the amount of heat of the fuel supplied into the cylinder, characterized in that in an efficient k is converted into heat generation quantity in the cylinder How to determine Wiebe function parameters. Relationship storage means for storing the relationship between the operating condition of the internal combustion engine and the maximum heat generation rate crank angle, which is the crank angle at which the actual heat generation rate in the cylinder is maximum;
Based on the Wiebe function model, heat generation rate estimation means for calculating a model heat generation rate for each crank angle, which is an estimated value of the heat generation rate in the cylinder,
With
The heat generation rate estimation means is arranged so that the crank angle at which the model heat generation rate becomes maximum coincides with the maximum heat generation rate crank angle acquired according to operating conditions in accordance with the relationship stored in the relationship storage means. An apparatus for estimating a heat generation rate of an internal combustion engine, wherein the model heat generation rate is calculated. The relationship storage means further stores the relationship between the operating conditions of the internal combustion engine, the shape parameter that is a Wiebe function parameter, and the combustion period,
The heat generation rate estimation means has a maximum heat generation rate crank angle acquired according to operating conditions in accordance with the relationship stored in the relationship storage means, CAm [° ATDC], a shape parameter m, and a combustion period θ _p [ °], where a which is one of the Wiebe function parameters is a predetermined constant, and β is a value represented by the following equation (IV), the crank angle CAs [° BTDC] of the heat generation start point of the Wiebe function is 6. The heat generation rate estimation device for an internal combustion engine according to claim 5, wherein the model heat generation rate is calculated so as to be a value represented by the equation (V).

CAs = β × θ _p −CAm (V)

Images