JPH07269379A - Hc discharge amount calculating method at engine with supercharger and valve timing setting method - Google Patents

Abstract

PURPOSE:To realize the easy setting of valve timing by calculating an intake air filling amount and a new air blowing-through amount during a valve opening overlap period on the basis of intake and exhaust port prediction pressure and temperature, comparing its rate with the actual measurement value of an HC discharge amount, and calculating the HC discharge amount from its correlation characteristic. CONSTITUTION:An engine and various intake and exhaust fundamentals are set (S1), and the conditions of valve timing and an engine rotation number or the like are given (S2), and on the basis of these, the pressure and temperature of intake and exhaust ports 5, 6 are calculated by means of first dimension analysis (S3). Next, by making a first dimension analysis outcome a border condition, third dimension analysis is conducted only during an valve opening overlap period (S4), and the blowing-through amount of new air and a filling amount are sought and its ratio is calculated (S5). This valve and the new air amount conversion value of the capacity of a portion downstream of an injector are compared with each other, and in the case of being large, its conversion value is made to be a new air blowing-through amount. The correlation of an actually measured HC discharge amount and a calculated value is sought (S7), and an HC discharge amount due to blowing-through is sought (S8).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for calculating the amount of HC discharged from a turbocharged engine as a result of blow-through of fresh air during an intake / exhaust valve opening overlap period, and The present invention relates to a valve timing setting method based on the above.

[0002]

2. Description of the Related Art Recently, performance evaluation of automobile engines,
For design and the like, a method of obtaining various state quantities and the like by analysis and calculation using a computer has been proposed. For example, in Japanese Unexamined Patent Publication (Kokai) No. 3-95681, the engine and the starter are replaced with a vibration system including a spring element and a vibration element, and the vibration system is modeled to analyze the natural frequency, calculate modal mass, etc. A simulation method has been disclosed in which the vibration characteristic is obtained by utilizing the known single characteristic of the vibration system.

In addition, the document "Mazda Technical Report (1988 NO
6) ”shows a method of obtaining the pressure, temperature, flow rate, etc. of each part of the intake system of an engine, which is composed of a cylinder, a surge tank, an air cleaner, and an intake pipe therebetween, by computer simulation. In this method, the intake system is modeled as a combination of sub models such as a pipe model, a container model, and a boundary model, and the state quantity is calculated for each sub model. For example, for a pipe model, based on the conservation equations for the wall friction coefficient, bending loss, heat exchange with the pipe wall, mass, momentum and energy The state quantity after a minute time is obtained, and for the container model, the calculation such as the change of the state quantity in the container is calculated based on the energy balance equation. Then, the calculation for each model is repeated until the state quantities converge while mutually reflecting the calculated values.

In this way, analysis using a computer,
By calculating various state quantities by calculation, it is not necessary to make a trial manufacture each time to set or change specifications in the design stage, and to check the state quantity on a trial basis. And it is possible to easily make decisions such as specifications on the desk.

[0005]

By the way, in an engine with a supercharger in which a supercharger is provided in the intake passage, a valve open overlap period in which the exhaust valve open period and the intake valve open period overlap each other. While there is an advantage that the scavenging action inside the combustion chamber can be obtained by sending the fresh air pressurized by the supercharger into the combustion chamber, part of the fresh air blows through the exhaust port and The HC emissions may increase due to the fuel contained in the air. Since the amount of fresh air blown through is related to the length of the valve opening overlap period,
It is required to properly set the valve timing (length of the valve opening overlap period) of the intake / exhaust valve so as to suppress scavenging property and suppress an increase in HC emission amount due to blow-through of fresh air. Then, in order to study such requirements at the design stage or the like, it is necessary to examine the amount of HC emission due to blow-through of fresh air.

Conventionally, no method has been developed for accurately calculating the HC emission amount in such a case, and the HC emission amount is actually measured for the prototype. However, if it is desired to check the HC emission amount by changing the valve timing, specifications of the intake system, etc. at the design stage, it is necessary to make a prototype each time and measure it with a measuring device, which is very troublesome work. Will be things.

In view of the above circumstances, the present invention does not need to perform actual measurement each time when the HC emission amount due to blow-through of fresh air is changed by variously changing the valve timing and the like at the designing stage, etc. Provides a method for calculating the amount of HC emissions in a supercharged engine that can easily and accurately determine the amount of HC emissions, and by using this method, the valve timing can be easily set on the desk. It is an object to provide a valve timing setting method.

[0008]

According to a first aspect of the present invention, there is provided a method for calculating an amount of HC emissions in a supercharged engine, wherein an amount of HC emissions during a valve opening overlap period of intake / exhaust valves in a supercharged engine is calculated. This is a method of calculating, by setting the engine specifications, predicting the pressure and temperature of the intake and exhaust ports, and based on these, the amount of fresh air blown into the exhaust port and the combustion chamber during the valve opening overlap period. The amount of intake air to the intake air is calculated, and the blow-through ratio, which is the ratio of the blow-through amount to the fill amount, is calculated. Meanwhile, the HC discharge amount from the combustion chamber is measured, and the blow-through ratio under the same conditions. Of the HC emission amount is compared with the measured value of the HC emission amount to obtain a correlation characteristic showing the correspondence relationship between the blow-through ratio and the HC emission amount, and the HC emission amount under various conditions is calculated from this correlation characteristic. To do Those were.

In this method, a value obtained by converting the volume of a portion of the intake port downstream of the injector into a fresh air amount is compared with a calculated value of the fresh air blowing amount, and the fresh air blowing amount is When it is larger than the converted value of the volume downstream of the injector, it is preferable to use the converted value of the volume downstream of the injector as the fresh air blow-through amount (claim 2).

Further, the amount of fresh air blown through to the exhaust port is preferably obtained by performing a three-dimensional analysis on the transition of the mixed state of the fresh air and the existing gas over the intake port, the combustion chamber and the exhaust port ( Claim 3).

In the third aspect of the invention, the pressure and temperature of the intake / exhaust port are obtained by one-dimensional analysis, and the three-dimensional analysis for obtaining the amount of fresh air blown into the exhaust port is performed by the valve opening overlap period. It is preferable to carry out only inside (Claim 4).

Further, based on the above three-dimensional analysis, the ratio of the fresh air ratio in the exhaust gas and the fresh air ratio in the combustion chamber gas is given by an approximate expression, and when the HC emission amount is subsequently calculated, the above approximate expression is given. It is preferable to calculate the blow-through ratio by using one-dimensional analysis (claim 5).

According to a sixth aspect of the present invention, there is provided a valve timing setting method which compares the HC exhaust amount obtained by the HC emission amount calculating method according to any one of the first to fifth aspects with the intake / exhaust valve valve timing. The amount of HC discharged at various valve timings is checked, and the valve timing is set based on this.

[0014]

According to the HC emission amount calculating method of the first aspect, the blow-through ratio, which is the ratio between the blow-through amount and the filling amount of fresh air during the valve opening overlap period, is calculated. Although the absolute value of the HC emission amount cannot be known only by this blow-through ratio, the calculated value of this blow-through ratio and H
The blow-through rate and H
A correlation characteristic with the C emission amount is obtained, and the HC emission amount can be obtained easily and accurately by calculation from the correlation characteristic according to the calculated value of the blow-through ratio. The actual measurement of the HC emission amount is performed only when the correlation is obtained, and after the correlation characteristic is obtained, the HC emission amount is calculated without requiring the actual measurement.

In this method, according to the second aspect, when the fresh air from the upstream of the injector that does not contribute to the HC emission amount is included in the blow-through amount, that amount is excluded from the calculated value of the blow-through amount. As a result, the above correlation characteristics can be obtained with high accuracy.

Further, according to the third aspect, the blow-through amount of the fresh air can be accurately obtained by the three-dimensional analysis, and accordingly, the blow-through ratio and the correlation characteristic can be accurately obtained.

According to the fourth aspect, the pressure and temperature of the intake / exhaust port can be easily and accurately obtained by the calculation by the one-dimensional analysis, and the three-dimensional analysis is more complicated than the one-dimensional analysis. In this case, only the above-mentioned valve opening overlap period should be performed.

According to the fifth aspect, after the approximate expression is given, the blow-through ratio is calculated by one-dimensional analysis using the approximate expression, so that the calculation is simplified and the calculation time is shortened. To be done.

According to the valve timing setting method of the sixth aspect, the above-mentioned HC emission amount calculation method is utilized,
The valve timing can be easily set.

[0020]

DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 schematically shows an engine with a supercharger. In this figure, each cylinder 1 of the engine has an intake passage 2
And the exhaust passage 3 are connected, and the combustion chamber 4 of each cylinder 1 is connected.
An intake port 5 on the downstream end side of the intake passage and an exhaust port 6 on the upstream end side of the exhaust passage are open at. A supercharger 7 is provided in the intake passage 2, and a mechanical supercharger is provided in the illustrated example. Further, the intake passage 2 is provided with an intercooler 8, a surge tank 9 and the like, and an injector 10 for injecting fuel is arranged near the intake port.

FIG. 2 schematically shows the combustion chamber 4 and the port portion. In this figure, the intake port 5 and the exhaust port 6 are provided with an intake valve 11 and an exhaust valve 12 for opening and closing the respective ports. Then, as is generally known, the exhaust valve 12 is opened in the exhaust stroke, and the intake valve 11 is opened in the intake stroke following the exhaust stroke, but the opening periods of both of them partially overlap. In addition, in this figure, the fresh air 15 is shown in a dotted manner, and the flow of the fresh air 15 during the valve opening overlap period of the intake / exhaust valves 11 and 12 is shown by an arrow.

As shown in this figure, in the engine with a supercharger, a part of the fresh air 15 pressurized by the supercharger 7 and fed into the combustion chamber 4 is exhaust port during the valve opening overlap period. It may blow through to 6. In this case, as the flow of the fresh air flowing into the combustion chamber 4 from the vicinity of the intake valve 11 toward the exhaust port 6, in addition to the flow straightly passing through the central portion of the combustion chamber 4 toward the exhaust port 6 side, 4 There is also a flow that goes around the outer peripheral side and the lower side of the intake valve 11 toward the exhaust port 6 and is three-dimensional.

In the method of the present invention, the movement and distribution of the fresh air 15 during the overlap period as described above is calculated by computational fluid dynamics (C
FD), especially considering that the flow of the fresh air 15 to the exhaust port 6 side is three-dimensional as described above, the analysis is performed by the three-dimensional CFD program, and during the overlap period. The amount of fresh air blown into the exhaust port 6 and the amount of intake air charged into the combustion chamber 4 are calculated, and the amount of fresh air 15 blown through with respect to the above-mentioned charged amount is calculated. The filling amount can be obtained by one-dimensional analysis.

In the analysis by the three-dimensional CFD, the engine specifications are set, the pressures and temperatures of the intake / exhaust ports 5 and 6 are predicted, and the analysis is performed based on these.
Calculate. At this time, preferably, the pressure and temperature of the intake / exhaust ports 5 and 6 are calculated by performing an analysis by one-dimensional CFD for all of the intake / exhaust systems, and the above three-dimensional analysis is opened with these as boundary conditions. Perform in the overlap period. It is also possible to set constant values as the predicted values of the pressures and temperatures (boundary conditions) of the intake / exhaust ports 5 and 6 and perform the analysis by the three-dimensional CFD for one cycle of the engine. However, the three-dimensional analysis is more complicated in calculation than the one-dimensional analysis, and if the three-dimensional analysis is performed over one cycle of the engine, the amount of calculation becomes enormous and the calculation processing time increases. It is preferable to perform the three-dimensional CFD for the valve opening overlap period with the value obtained by the original analysis as the boundary condition.

As the above-mentioned one-dimensional CFD program,
Use a program that can calculate the boost pressure based on the specifications of the engine and intake / exhaust system.

The program of the three-dimensional CFD can handle the operation of intake / exhaust valves and pistons, can consider the mixture of two kinds of gas of intake and exhaust, and can pass through each valve. The program that satisfies each condition that the time change of the gas of is known is used. Such a three-dimensional CFD program has already been developed.

The outline of the method of three-dimensional analysis during the valve opening overlap period using this program will be explained. In the analysis, as shown in FIG. 3, the analysis is performed over the intake port 5, the combustion chamber 4 and the exhaust port 6. Set up a 3D mesh for. Then, with respect to each part of the three-dimensional mesh, the change in the mixing ratio of the fresh air and the existing gas (residual gas in the combustion chamber and exhaust gas) at each constant minute time is repeatedly calculated. Thus, it is possible to analyze and calculate the distribution state of fresh air at each time point for each minute time during the valve opening overlap period.

FIG. 4 shows a change in the distribution state of the fresh air 15 within the valve opening overlap period examined by such a three-dimensional analysis, and is shown in time series from the midpoint of the valve opening overlap period. 4 (a), (b), and (c), the distribution state of the fresh air 15 changes, and the fresh air gas concentration in the exhaust port 6 gradually increases. Then, the fresh air blow-through amount is calculated from the change of the fresh air distribution state in the exhaust port portion at each constant minute time, and by integrating this over time, the fresh air blow-through amount during the valve opening overlap period is calculated. You can

The overall procedure of the HC emission amount calculation method is shown in FIGS. 5 and 6.

Explaining the procedure shown in FIG. 5, first, engine specifications including main engine specifications such as combustion chamber shape and intake / exhaust system specifications are set (step S1). next,
Engine operating conditions such as valve timing and engine speed are given (step S2). Then, the pressure and temperature of the intake / exhaust ports 5 and 6 are calculated by analysis of the entire intake / exhaust system by the one-dimensional program based on the engine specifications and the like (step S3).

Next, the three-dimensional program is used to perform the three-dimensional analysis for the valve opening overlap period with the one-dimensional analysis result as a boundary condition (step S4). And
The blow-through amount and filling amount of fresh air during the valve opening overlap period are obtained, and the blow-through ratio (fresh air blowing amount / filling amount) is calculated (step S5).

In this case, the value obtained by converting the volume of the portion of the intake port 5 downstream of the injector 10 into a fresh air amount is compared with the fresh air blowing amount obtained by the three-dimensional analysis, and the new air blowing amount is compared. When the air blowing amount is larger than the converted value of the volume downstream of the injector, the converted value of the volume downstream of the injector is set as the fresh air blow-through amount. This is done in order to ensure the correspondence relationship between the blow-through ratio and the HC emission amount, which will be described later. That is, when the fresh air blowing amount becomes larger than the converted value of the volume of the injector downstream, the fresh air from the injector upstream is also blown through, but HC is discharged during the valve opening overlap period. This is because the fuel injected from the injector and mixed with the fresh air on the downstream side is blown through, so the fresh air from the injector upstream does not contribute to the HC emission amount, and the fresh air blown through including this is blown out. The quantity will no longer correspond to the HC emissions. Therefore, the fresh air from the injector upstream is excluded from the fresh air blow-through amount.

The processes of steps S2 to S5 are repeated a plurality of times by changing the valve timing, the engine speed, etc., that is, the three-dimensional analysis is carried out under a plurality of engine operating conditions to determine the blow-through ratio. calculate.

On the other hand, the HC emission amount of the actual machine is actually measured (step S6). This actual measurement is also performed multiple times by changing the engine operating conditions, and at least twice.

Then, the above steps S2 to S5.
After repeating the above process a plurality of times, the blow-through amount and the HC discharge amount as shown in FIG. 7 are calculated based on the comparison between the calculated value of the blow-through ratio and the measured value of the HC discharge amount under the same engine operating condition. Correlation characteristics showing the correspondence relationship of are obtained (step S7). That is, since the blow-through amount and the HC discharge amount have a linear correspondence relationship, the blow-through ratio calculated value and the HC discharge amount measured value under the same engine operating condition are regarded as one set, and a plurality of sets (at least two sets) are set. By comparing the calculated value of the blow-through ratio and the actual measured value of the amount of discharged HC, the correlation characteristic as shown in FIG. 7 can be obtained. Then, this correlation characteristic is stored in the form of, for example, a functional expression.

After obtaining the correlation in this way, the HC emission amount can be obtained from the above correlation characteristics in accordance with the calculated value of the blow-through ratio other than the values compared in step S7. Therefore, under various engine operating conditions. The HC emission amount is obtained according to the calculated value of the blow-through ratio in step S8.

As the processing based on the three-dimensional analysis, in addition to the processing of steps S5, S7, and S8, processing for incorporating the tendency of the three-dimensional analysis result into the one-dimensional program (step S9) is performed. It is preferable. As this processing, based on the above three-dimensional analysis, the ratio between the fresh air ratio in the exhaust gas and the fresh air ratio in the combustion chamber gas at various points during the valve opening overlap period is calculated, and this ratio and crank angle are calculated. The correspondence relationship between and is given by an approximate expression, and the values that define this approximate expression are stored as a map.

This processing will be specifically described. The fresh air ratio Ra in the exhaust gas and the fresh air ratio Rb in the combustion chamber corresponding to the crank angle during the valve opening period as shown in FIG. 8 can be obtained by the three-dimensional analysis. Here, the fresh air ratio Ra in the exhaust gas is (amount of fresh air passing through the exhaust valve) /
(Total gas amount passing through the exhaust valve), and the fresh air ratio Rb in the combustion chamber is (new air amount in the combustion chamber) / (total gas amount in the combustion chamber).

Taking the ratio (Ra / Rb) between the fresh air ratio Ra in the exhaust gas and the fresh air ratio Rb in the combustion chamber, the relationship between this ratio and the crank angle is shown by lines ab and ab in FIG. b
It can be approximated to the form of c and can be represented by an approximate expression. This approximate characteristic (value of points a, b, c)
Varies depending on the valve timing, engine speed, etc. Therefore, based on three-dimensional analysis performed under several kinds of engine operating conditions, the tendency of the ratio (Ra / Rb) is obtained, and the data of points a, b, c, etc. that define the approximate expression are loaded as a map, An approximate expression should be obtained from this map according to engine operating conditions.

By doing so, it is not necessary to perform a three-dimensional analysis thereafter, and it becomes possible to approximately calculate the blow-through ratio by an analysis by a one-dimensional program as shown in FIG.

Explaining the procedure shown in FIG. 6, first,
Engine specifications including main engine specifications such as combustion chamber shape and intake / exhaust system specifications are set (step S11).
Next, engine operating conditions such as valve timing and engine speed are given (step S12).

Next, the supercharging pressure is calculated by one-dimensional analysis, and the approximation obtained according to the engine operating conditions and the like from the data taken into the one-dimensional program in the process of step S9 of FIG. 5 described above. The blow-through ratio is calculated using the formula (step S13). Then, the HC emission amount is calculated from the correlation characteristic obtained in the process of step S7 of FIG. 5 according to the blow-through ratio (step S).
14).

According to the above HC emission amount calculating method, the blow-through ratio is obtained by calculation, and particularly when the procedure shown in FIG. 5 is executed, the blow-through amount of fresh air is determined by the three-dimensional analysis in step S4. It is obtained with high accuracy, and therefore the blow-through rate is calculated with high accuracy. Also,
Although the absolute value of the HC emission amount cannot be known only by this blow-through ratio, the correlation characteristic between the blow-through ratio and the HC emission amount is obtained based on the comparison between the calculated value of this blow-through ratio and the measured value of the HC emission amount ( In step S7), the HC emission amount can be calculated easily and accurately according to the calculated value of the blow-through ratio from this correlation characteristic.

In this case, although the HC emission amount is actually measured (step S6) in order to obtain the correlation, the HC emission amount is calculated only by using the correlation characteristic after obtaining the correlation characteristic. The amount can be obtained, and it is not necessary to actually measure the amount of HC emission each time when the amount of HC emission is newly obtained by changing the valve timing or the like.

Further, in the procedure shown in FIG. 5, if the tendency of the three-dimensional analysis result is fetched into the one-dimensional program by the processing of step S9, the HC is newly added after that.
When calculating the emission amount, HC
Emissions can be calculated and calculation time can be shortened. In this case, an accurate approximation value can be obtained by using an approximate expression for the ratio of the fresh air ratio Ra in the exhaust gas and the fresh air ratio Rb in the combustion chamber.

Further, by using such an HC emission amount calculating method, it is possible to easily set an appropriate valve timing. This valve timing setting method is illustrated in FIG.

In the example shown in FIG. 6, the HC discharge amount is calculated under various engine operating conditions, especially at various valve timings, and the valve timing and HC discharge amount are compared with each other to compare the valve timing and the HC discharge amount. Examine the relationship with emissions. Then, based on this, for example, by selecting a valve timing such that the HC discharge amount satisfies the required value, an appropriate valve timing is set (step S15).

Of the methods shown in FIGS. 5 and 6, the content of the method for obtaining the pressure and temperature of the intake / exhaust port by one-dimensional analysis is not limited by the present invention. An example of a method capable of calculating the boost pressure will be described below with reference to FIGS. 1 and 10 to 12. Although the intake system is shown in the figure, the exhaust system may be analyzed in accordance with the intake system.

In this method, for example, the simulation model of the intake system shown in FIG. 1 is set as follows.
That is, the intake system including each cylinder 1 of the engine is divided into an intake system model excluding the supercharger 7 and a supercharger model.
The intake system model (the part surrounded by the broken line) is a pipe model showing the intake pipe of each part of the intake passage 2, a container model showing the intercooler 8, the surge tank 9, each cylinder 1, etc., and the pipe and the container. It shall consist of sub-models such as the model of the boundary part between and. As shown in FIG. 10, the supercharger model models the supercharger 7 into two containers 7a and 7b on the suction side and the discharge side, that is, the suction side container 7a and the upstream intake pipe. Inhalation side model 21 showing the connection part with
And a discharge-side model 22 that represents a connecting portion between the discharge-side container 7b and the downstream intake pipe.

FIG. 11 shows a schematic procedure of the arithmetic processing by the above simulation model. As the procedure, first, the pressure of each part in the intake system model and the supercharger model,
Initial values of state quantities such as temperature are set (step S2).
1). Next, after setting the time for assuming the passage of time (step S22), as the intake system state quantity calculation processing, the calculation processing for each pipe model (step S22) is performed.
23), the calculation process for each container model (step S24), and the calculation process for the model of the boundary between the pipe and the container (step S25), while the supercharger state for the supercharger model is performed. Quantity calculation processing (step S
26) is performed. Then, these steps S23 to S2
After performing each of the arithmetic processes of 6, the process returns to step S22, and the arithmetic processes of steps S23 to S26 are performed again on the assumption that a certain minute time has elapsed due to the time setting. In this way, until each state quantity converges,
The above-mentioned arithmetic processes are repeatedly performed at a constant, minute assumed time interval.

In the calculation process of step S23, the pipe is divided into equal parts based on the conservation equations of mass, momentum and energy in consideration of wall friction coefficient, bending loss, heat exchange with the pipe wall, etc. for the pipe model. The state quantities such as pressure and temperature of each part in the pipe are obtained by obtaining the state quantities after a minute time from the state quantities at the respective divided points. In step S24, the container model is subjected to calculation such as a change in the state quantity in the container based on the energy balance equation.

In step S25, the conservation equations of energy and mass between the pipe end portion, the boundary between the pipe and the container, and the container portion are used, and the correlation with the state quantity of the pipe model is considered. Then, the state quantity at the pipe end is obtained by establishing a simultaneous equation.

These calculation processes are also shown in the above-mentioned document "Mazda Technical Report (1988 NO6)".

Further, in the supercharger state quantity calculation process of step S26, the supercharger model shown in FIG. 10 is used, and the data of the characteristic of the single supercharger that has been examined in advance is used. The characteristic data of the supercharger itself is obtained by performing a steady flow test on a mechanical supercharger to be used in advance. In other words, when a mechanical turbocharger was prototyped and variable throttles were attached to its suction side and discharge side, the supercharger was operated at various rotational speeds, and the throttles were changed variously,
The pressure ratio (ratio between discharge pressure and suction pressure), discharge flow rate, temperature change amount (difference between discharge side temperature and suction side temperature), and the like are obtained based on measurement, and their relationship is investigated. As a result, the relationship between the pressure ratio and the discharge flow rate at various supercharger rotation speeds,
Further, a map of supercharger characteristic data as shown in FIG. 13 showing the relationship between these and the temperature change amount is obtained.

These relationships are mapped.

Then, the supercharger state quantity calculation process is specifically performed as shown in FIG.

That is, first, for the discharge side model 22 of the supercharger models, the pressure Pvo in the container 7b is assumed (step S31), and the discharge side flow rate Mo is obtained (step S32). Next, regarding the suction side model 21,
The pressure Pvi in the container 7a is assumed (step S33), and the flow rate Mi on the suction side is obtained (step S34). As the respective calculation processes shown in steps S32 and S34, the pressures Pvo and Pvi in the container, the temperatures Tvo and Tvi, the pressures Pto and Pti of the throttle (between the pipes of the container), the temperatures Tto and Tti, and the flow velocity are the same. u
to, uti, same cross-sectional area Ato, Ati, pipe end pressure Ppo,
With respect to the relationship among Ppi, the same temperatures Tpo and Tpi, the same flow velocities upo and upi, the same cross-sectional areas Apo and Api, the same calculation as the calculation of the boundary model (step S25) is performed. However, as described above, the pressures Pvo and Pvi in the container are assumed values.

Next, since the suction flow rate and the discharge flow rate of the supercharger should be equal to each other, the above step S32 and step S
It is checked whether or not the flow rates Mo and Mi respectively obtained by 34 and 34 are equal (step S35), and if they are not equal, the assumed value of the pressure Pvi of the container 7a in the suction side model 21 is changed, and then the suction side is newly determined. The flow rate Mi on the suction side is obtained by the calculation process for the model 21. In this way, while changing the assumed value of the pressure Pvi, step S3
By repeating S3 and S34, the above flow rates Mo, Mi
Search for a condition where are equal.

When a state in which the flow rates Mo and Mi are equal to each other is obtained, from the discharge pressure (pipe end pressure on the discharge side) Ppo and the suction pressure (pipe end pressure on the suction side) Ppi obtained by the arithmetic processing,
The pressure ratio Pr is obtained (step S36). And FIG.
From the map of the supercharger characteristic data shown in FIG. 3, the discharge flow rate Mmap corresponding to the pressure ratio obtained in step S36 and the set turbocharger rotation speed is obtained (step S37), and the discharge flow rate obtained in step S32 is obtained. Mo is compared with the discharge flow rate Mmap obtained from the map of the supercharger characteristic data (step S38). That is, the discharge flow rate Mo and the discharge flow rate Mmap according to the characteristic map are the same as the supercharger rotation speed,
It is checked whether they are equal under the condition of the same pressure ratio, and if they are not equal, the assumed value of the container pressure Pvo in the above-mentioned discharge side model is changed, and the processes of steps S31 to S38 are performed again, and Mo = Mmap Until step S31
~ The process of S38 is repeated.

When Mo = Mmap, the drawing is performed according to the suction side temperature (temperature of the pipe end on the suction side of the supercharger) Tpi and the supercharger rotation speed, the pressure ratio, and the discharge flow rate, which are obtained by the calculation process. Based on the temperature difference obtained from the characteristic map of No. 13, the discharge side temperature (temperature of the supercharger discharge side pipe end) Tpo is obtained (step S39). Further, the discharge pressure Ppo, which is the other state quantity at the pipe end, is determined by the final calculated value by the calculation process (step S32 and step S34) (step S40).

In the calculation of the discharge side model and the suction side model in such supercharger state quantity calculation processing, the calculation of the pipe model in the intake system state quantity calculation processing is reflected. Further, the state quantity of the tube end obtained by the supercharger state quantity calculation process is reflected in the next calculation of the pipe model and the like during the repetition of each calculation process shown in FIG. 11.

In this way, step S2 in FIG.
Inhalation system state quantity calculation process including each process of 3 to S25 and step S including steps S31 to S40 of FIG.
26 and 26 are repeatedly performed while reflecting the calculation results momentarily, until the state quantities converge.

With such a method, the supercharging pressure (discharge pressure) and other state quantities can be obtained, and the boundary condition for the three-dimensional analysis can be given in the procedure shown in FIG. it can.

[0064]

As described above, the HC emission amount calculating method of the present invention is based on the engine specifications and the pressure and temperature of the intake / exhaust ports in the engine with a supercharger, and is used during the valve opening overlap period. The blow-through amount and the filling amount of air are calculated to calculate the blow-through ratio, the calculated value of the blow-through ratio under the same conditions and the measured value of the HC emission amount are compared to obtain a correlation characteristic, and various conditions are obtained from the correlation characteristic. Since the HC emission amount below is calculated, if the actual measurement of the HC emission amount is performed in order to obtain the above correlation, then the HC emission amount can be calculated easily and accurately by the intake blow-by. Emissions can be calculated.

Particularly, if the amount of fresh air blown into the exhaust port is obtained by three-dimensional analysis, the accuracy can be improved.

Further, based on the above three-dimensional analysis, the ratio of the fresh air ratio in the exhaust gas and the fresh air ratio in the combustion chamber gas is given by an approximate expression, and when the HC emission amount is subsequently calculated, the above approximate expression is given. If the blow-through ratio is calculated by one-dimensional analysis using, it is possible to simplify the calculation while ensuring sufficient accuracy.

Further, in the valve timing setting method utilizing the above HC discharge amount calculation method, the HC discharge amount at various valve timings is obtained by the above calculation method, and the valve timing is set based on this.
Effective valve timing can be easily set.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing an example of a supercharged engine to which the method of the present invention is applied.

FIG. 2 is a diagram schematically showing a combustion chamber and a port portion.

FIG. 3 is an explanatory diagram showing a three-dimensional mesh for three-dimensional analysis.

4 (a), (b) and (c) are explanatory views showing a transition of a distribution state of fresh air in a combustion chamber and a port portion within a valve opening overlap period.

FIG. 5 is an explanatory diagram showing an example of a procedure of a method for calculating an HC emission amount according to the present invention.

FIG. 6 is an explanatory diagram showing a part of a procedure of an HC emission amount calculation method and a valve timing setting method.

FIG. 7 is a diagram showing a correlation characteristic between a blow-through ratio and an HC emission amount.

FIG. 8 is a diagram showing changes in a fresh air ratio in a combustion chamber and a fresh air ratio in exhaust gas during a valve opening overlap period.

FIG. 9 is a diagram approximately showing a ratio between a fresh air ratio in a combustion chamber and a fresh air ratio in exhaust gas during a valve opening overlap period.

FIG. 10 is a diagram showing a supercharger model.

FIG. 11 is a diagram showing an overall procedure of an example of a method of calculating an intake system state quantity.

FIG. 12 is a diagram showing a part of an example of a method of calculating an intake system state quantity.

FIG. 13 is a diagram showing a map of supercharger characteristic data.

[Explanation of symbols]

 1 Cylinder 5 Intake port 6 Exhaust port 7 Supercharger 11 Intake valve 12 Exhaust valve 15 Fresh air

Claims (6)

[Claims] 1. A method for calculating the HC emission amount during the valve opening overlap period of an intake / exhaust valve in a supercharged engine, wherein engine specifications are set, and pressures and temperatures of intake / exhaust ports are set. Is calculated based on these values, the amount of fresh air blown into the exhaust port and the amount of intake air charged into the combustion chamber during the valve overlap period are calculated, and this is the ratio of the amount of blowout to the amount of fill. The blow-through ratio is calculated, on the other hand, the HC discharge amount from the combustion chamber is measured, and the calculated value of the blow-through ratio and the measured value of the HC discharge amount under the same conditions are compared to determine the blow-through ratio and the HC discharge. A method for calculating the amount of HC emission in a supercharged engine, comprising: obtaining a correlation characteristic showing a correspondence relationship with the amount, and calculating the amount of HC emission under various conditions from the correlation characteristic. 2. A value obtained by converting the volume of a portion of the intake port downstream of the injector into a fresh air amount is compared with a calculated value of the fresh air blowing amount, and the fresh air blowing amount is determined by the injector downstream. 2. The method for calculating the amount of HC emissions in a supercharged engine according to claim 1, wherein the converted value of the volume downstream of the injector is set as the fresh air blow-through amount when the calculated value is larger than the converted value of the volume. 3. The amount of fresh air blown into the exhaust port is obtained by performing a three-dimensional analysis on the transition of the mixed state of the fresh air and the existing gas over the intake port, the combustion chamber and the exhaust port. The method for calculating the amount of HC emissions in a supercharged engine according to claim 1 or 2. 4. The pressure and temperature of the intake / exhaust port are obtained by one-dimensional analysis, and the three-dimensional analysis for obtaining the amount of fresh air blown into the exhaust port is performed only during the valve opening overlap period. The method for calculating the amount of HC emissions in a supercharged engine according to claim 3. 5. Based on the above three-dimensional analysis, the ratio between the fresh air ratio in the exhaust gas and the fresh air ratio in the combustion chamber gas is given by an approximate expression, and when the HC emission amount is subsequently calculated, the approximate expression is used. The method for calculating the amount of HC emissions in a supercharged engine according to claim 3 or 4, wherein the blow-through ratio is calculated by a one-dimensional analysis. 6. The HC according to any one of claims 1 to 5.
The valve is characterized by comparing the HC exhaust amount obtained by the exhaust amount calculation method with the valve timing of the intake / exhaust valve, checking the HC exhaust amount at various valve timings, and setting the valve timing based on this. Timing setting method.