KR100927392B1 - Estimation method of urban mean effective pressure of internal combustion engine - Google Patents

Abstract

The present invention relates to a method for estimating the urban average effective pressure of an internal combustion engine, which can reduce the amount of computational work by using a small number of cylinder pressure data and can estimate the urban average effective pressure simply and accurately. In the method for estimating the urban mean effective pressure of an internal combustion engine according to the present invention, a method for estimating the average mean effective pressure in a cylinder for an internal combustion engine including a cylinder and a piston reciprocating linearly in the cylinder is provided. At the position where the crank connected to the piston is further rotated by a preset reference angle from the reference rotation position at the top dead center position of the piston, the actual pressure and the crank in the cylinder are rotated less by the reference angle before the reference rotation position. Measuring the actual pressure inside the cylinder, and obtaining a difference in the measured pressures; Measuring the angle of the crank when the difference between the actual pressure inside the cylinder and the motoring pressure inside the cylinder becomes a preset reference pressure; And estimating the city average effective pressure in the cylinder using the pressure difference in the cylinder and the measured crank angle.

Common-rail direct injection, dedicated mean effective pressure, dedicated work, motoring pressure

Description

Method for estimating indicated mean effective pressure using cylinder pressure}

The present invention relates to a method of estimating the urban average effective pressure of an internal combustion engine, and more particularly, to a method of estimating the urban average effective pressure which is widely used as a measure of the performance of an internal combustion engine.

The engine of an internal combustion engine, for example a motor vehicle, comprises a cylinder and a piston reciprocating linearly in the cylinder, and when fuel burns in the cylinder, dedicated work is produced. And, the illustrated work is transmitted to each drive unit through the crank shaft connected to the piston, so that the vehicle can be driven.

On the other hand, the multi-cylinder automobile engine is provided with a plurality of cylinders, and combustion occurs in a predetermined order in the plurality of cylinders, and the cylinder pressure is continuously converted to the rotation day of the crankshaft. The torque generated on the crankshaft has a great influence on the drivability of the vehicle. By design, the same size torque is generated in each cylinder, but in reality, there is a difference in the amount of fuel burned or the amount of air sucked into the cylinder due to various factors such as production tolerances and aging of engine parts. This difference causes a difference in the torque generated in each cylinder.

The difference in torque generated for each cylinder is obtained by measuring the torque coming out of the crankshaft directly. However, the torque sensor for measuring torque has a problem that durability is not only being verified, but also expensive, and that reliability of torque data measured by the torque sensor is still being verified, and the method disclosed in Korean Patent No. 510,804 is a map. It required a lot of tests when constructing the engine and moreover it was very vulnerable to aging and disturbance of engine parts.

In addition to this, there is a method of using the city average effective pressure as a method of measuring torque variation for each cylinder. The city average effective pressure is best suited for calculating city torque since it is derived from a cylinder pressure that provides instant combustion information. In particular, the pressure sensor for measuring cylinder pressure includes atmospheric pressure, mass airflow, and camshaft. Since it is possible to replace a sensor such as a sensor, measuring or estimating the city average effective pressure using cylinder pressure is more accurate and economical than using torque. The average urban effective pressure is calculated by Equation 1 below.

Here, n ₁ and n ₂ are integration periods, the initial and the last of the crank angle, Δθ are the resolution of the crank angle, V _S is the displacement of the cylinder, P is the cylinder pressure.

However, since the cylinder pressure data for the entire cycle is required to calculate the city average effective pressure, 720 data are required for one cylinder when sampling the cylinder pressure for each 1 degree of the crank. In the case of a four-cylinder engine, 2880 data sampling and calculations must be completed in one cycle. Such an excessive amount of calculation has a problem that a high performance controller as well as a commercial engine controller are difficult to perform in real time. And, in order to reduce the workload of the controller, which was proposed in 1996 by Brunt and Empire, an error is obtained when obtaining a city average effective pressure (Coarse IMEP) with a wider sampling interval of cylinder pressure. A new problem arises that is increased.

Therefore, the necessity of researching a new pressure variable that can represent the urban mean effective pressure has emerged.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and an object of the present invention is to reduce the amount of computational work by using a small number of cylinder pressure data, and to provide an internal combustion engine capable of estimating the city average effective pressure simply and accurately. It is to provide a method for estimating the urban mean effective pressure.

In order to achieve the above object, the urban mean effective pressure estimation method of an internal combustion engine according to the present invention is an average mean effective pressure inside the cylinder for an internal combustion engine including a cylinder and a piston reciprocating linearly in the cylinder. In the method for estimating an effective pressure, the actual pressure and the crank inside the cylinder at the position where the crank connected to the piston is further rotated by a predetermined reference angle from the reference rotation position at the top dead center position of the piston Measuring the actual pressure inside the cylinder at a position which is rotated less by the reference angle before the position of rotation, thereby obtaining a difference between the measured pressures; Measuring an angle of the crank when the difference between the actual pressure inside the cylinder and the motoring pressure inside the cylinder becomes a preset reference pressure; And estimating the city average effective pressure inside the cylinder by using the pressure difference in the cylinder and the measured crank angle.

According to the invention, DP _deg And CA _DP can be used to estimate the city average effective pressure simply and accurately. In particular, unlike the prior art, a small number of cylinder pressure data, ie DP _deg And by using the CA _DP , it is possible to reduce the amount of computational work and further to estimate the city average effective pressure in real time.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to FIGS. 1 to 10.

First, a process of selecting a new variable that can represent the urban mean effective pressure will be described.

The effective mean urban pressures are: peak cylinder pressure, location of peak pressure, peak of pressure (peak of pressure ratio), center of pressure difference (COG _y _PR; center) of gravity of difference pressure, difference pressure integration, modified pressure ratio (MPR), cylinder-pressure difference between 60 ° and 60 ° before top dead center (DP _deg) . firing and motoring at 60 ° canc angle after top dead center (ATDC), cylinder pressure at top dead center, and crank between cylinder pressure with the crank rotated 60 ° further from the reference rotational position It has a correlation with pressure variables such as difference (P _{@ 60 ° ATDC} ). Then, the correlation coefficient γ representing the correlation between the pressure variable and the urban mean effective pressure was obtained by Equation 2, and summarized in Table 1.

Here, n, x and y represent the number of samples, the city average effective pressure and the pressure variable, respectively.

In particular, Table 1 lists only the pressure variables that have a high correlation with the urban mean effective pressure. Therefore, the pressure variable having a low correlation with the city average effective pressure, for example, the position of the peak pressure having a correlation of 0.264, and the like are omitted.

)간의 상관관계를 그래프로 도시하였다. 도 1에 도시되어 있는 바와 같이 도시평균유효압력은 각 압력변수와 선형 관계에 있으며, 따라서, 도시평균유효압력의 추정식은 <수학식 3>에 의해 얻어진다. Then, the experiment was performed at a specific speed, for example, an engine speed of 1500 rpm, and the pressure variable and estimated urban mean effective pressure (

The correlation between) is shown graphically. As shown in FIG. 1, the city average effective pressure has a linear relationship with each pressure variable, and therefore, the equation of the city average effective pressure is obtained by Equation 3.

Meanwhile, in order to derive a pressure variable having a higher correlation with the urban mean effective pressure among the pressure variables summarized in <Table 1>, the correlation coefficient γ and the error of the estimated urban mean effective pressure (percent error 2-norm) are calculated < Table 2 is summarized as follows. Here, the error of the correlation coefficient γ and the estimated urban mean effective pressure was obtained at an engine speed of 1500 rpm, and the error was calculated by Equation 4.

Here, n and x represent the error of the number of samples and the city average effective pressure. IMEP _measured and IMEP _estimated represent the measured city average effective pressure and estimated city average effective pressure, respectively.

Table 2 shows the error between the correlation coefficient γ and the measured average mean effective pressure (IMEP _measured ) and estimated average mean effective pressure (IMEP _estimated ).

Referring to <Table 2>, DP _deg And DP _{@ 60 ° ADTC} has the highest correlation coefficient and low error. And DP _deg And DP _{@ 60 ° ADTC} are both obtained using the cylinder pressure at only two points, and the calculation method is simple. However, to obtain DP _{@ 60 ° ADTC} , another calculation process is needed to find the motor pressure of the cylinder. Therefore, it can be concluded that it is preferable to use DP _deg to represent the urban average effective pressure. As such, DP _deg is used as a pressure variable representing the city average effective pressure. The difference in cylinder pressure (ΔP _deg ) before and after the top dead center is greatly influenced by the displacement, which is why the combustion conditions of the engine It is also supported by the point monitored using the difference ΔP _deg . For example, ignition failure or partial combustion is successfully detected by ΔP _deg at the selected crank angle.

For reference, FIG. 3 shows a correlation for cylinder pressure and cylinder volume. Here, the gray area represents the city average effective pressure. And, the pressure difference between the two points for the DP _deg calculation corresponds to the height of the rectangle of FIG. As a result, DP _deg represents the city average effective pressure.

On the other hand, the DP _deg described above is well shown in Figure 2a, P < _{60 ° ATDC} as shown in <Equation 5> And P _{@ 60 ° BTDC} .

Here, P _{@ 60 ° ATDC} is the pressure inside the cylinder at the top dead center and the crank is rotated further by a preset reference angle, for example 60 °, from the reference rotational position at the top dead center position of the piston. It means the difference in pressure. And, P _{@ 60 ° BTDC} refers to the difference in pressure inside the cylinder at the top dead center and with the crank positioned at a preset reference angle less than 60 ° from the reference rotational position.

Next, the following experiments were conducted to verify whether the _DPG can be represented by the city average effective pressure alone.

A 2-liter in-line four-cylinder common-rail direct injection diesel engine with a turbocharger and an intercooler was prepared as shown in FIG. As the engine control system, a commercial off-the-shelf (COTS) rapid control prototyping (RCP) platform, MicroAutoBox, was used. Fuel injection timing, injection duration and common rail pressure were adjusted for each experiment. Cylinder pressure was measured using a piezo pressure transducer suitable for the glow plugs. Details of the experimental setup are shown in Table 3.

After configuring the experimental apparatus as shown in Table 3, the injection command, which is the time when external disturbance, injection period, and injection command is input, focusing on the fact that the city average effective pressure changes during the engine operation by the driver's request or external disturbance. The performance estimation of urban mean effective pressure fluctuated by SOE (Start of Energizing) was verified. Here, the injection period and the injection command period were separated and changed to stepwise. 4 and 5 illustrate the response of IMEP _measured , IMEP _estimated, and DP _{deg to} change of injection period and injection command timing.

Referring to FIG. 4, it can be seen that as the injection period increases, all of IMEP _measured , IMEP _estimated and DP _deg also increase. This means that the change in the urban mean effective pressure due to the change in injection period can be estimated successfully using DP _deg .

Referring to FIG. 5, it can be seen that as the injection command time is changed, the IMEP _measured is kept substantially the same but the IMEP _estimated and DP _deg are changed visually. This is due to the change of command injection timing IMEP _measured This means that the DP _deg changes more, so the IMEP _measured is different from the IMEP _estimated .

In conclusion, referring to FIGS. 4 and 5, it can be seen that the city average effective pressure cannot be effectively estimated using only DP _deg . In other words, it is not possible to successfully estimate the urban average effective pressure change for engine conditions other than the fuel amount. For this reason, pressure parameters other than DP _deg should be introduced.

In addition, DP _deg cannot represent the change of the city average effective pressure caused by the change of injection command timing. This is because the timing of the injection command also mainly affects the combustion pattern. Therefore, CA _DP10 , representing the ignition time, should be used to estimate the urban effective mean pressure with DP _deg . Here, CA _DP10 refers to the crank angle when the difference between the cylinder pressure P _firing and the _motoring pressure P _motoring becomes 10 bar, as shown in FIG. 2B. More specifically, the relationship between IMEP, CA _DP10 and DP _deg was obtained through experiments under specific engine operating conditions (1500 rpm, common rail pressure of 600 bar), which is shown in FIGS. 6 to 8. Referring to FIG. 7, it can be seen that the city average effective pressure also increases as the fuel amount increases. The urban mean effective pressure has a weak quadratic relationship with the injection order timing (SOE) and CA _DP10 . 8, it can be seen that as the DP _deg increases, the city average effective pressure also increases, and there is a weak quadratic relation between the city average effective pressure and DP _deg .

In conclusion, referring to FIGS. 7 and 8, the average urban effective pressure is CA _DP10 and DP _deg. It can be seen that they are in quadratic relation with each other. Therefore, the estimation formula of the city average effective pressure is derived from Equation 6.

는 추정 도시평균유효압력이고, x 및 y는 각각 DP_deg 및 CA_DP10이며, a, b, c, d, e 및 f는 비선형 커브 피팅(nonlinear curve fitting)에 의해 결정되는 상수이다. here,

Is the estimated urban mean effective pressure, and x and y are DP _deg respectively. And CA _DP10 , a, b, c, d, e and f are constants determined by nonlinear curve fitting.

Using Equation (6), it can be seen that the error is reduced from 32.807 to 15.756. In addition, it was confirmed that the urban mean effective pressure change caused by the injection command timing change is accurately estimated as shown in FIG. 9.

Equation 6 is also extended to operating conditions of various engines. In other words, even if the engine speed or pressure changes, a quadratic equation is established between the city average effective pressure, injection command timing (SOE) and CA _DP10 , and the city average effective pressure and DP _deg under constant engine operating conditions. Equation 6 can be applied.

As described above, when the urban mean effective pressure estimation method of this embodiment is used, DP _deg And CA _DP10 , the city average effective pressure can be estimated simply and accurately. In addition, unlike the conventional method, the computational load can be reduced.

As mentioned above, the present invention has been described in detail with reference to preferred embodiments, but the present invention is not limited to the above embodiments, and various modifications may be made by those skilled in the art within the technical idea of the present invention. It is obvious.

For example, the present embodiment discloses a method for estimating the city average effective pressure for a common rail direct injection diesel engine, but an internal combustion engine other than the common rail direct injection diesel engine, for example, a gasoline engine or another type. It is a matter of course that the method of estimating the city average effective pressure according to the present embodiment may also be applied to a diesel engine.

In addition, in the present embodiment, the reference angle is 60 ° and the reference pressure is set to 10 bar, but the reference angle and the reference pressure may be changed to other values.

1 is a graph showing the correlation between the city average effective pressure and the pressure variable.

2A and 2B are diagrams for explaining DP _deg and CA _DP10 , respectively, and are graphs showing a correlation between cylinder pressure and crank angle.

FIG. 3 is a graph for explaining the city average effective pressure, and is a graph illustrating conversion of a cylinder pressure and a cylinder volume into a log.

4 is a graph showing that the response of IMEP _measured , IMEP _estimated and DP _deg also changes as the injection period is changed stepwise.

5 is a graph showing that the response of IMEP _measured , IMEP _estimated and DP _deg also changes as the injection command timing changes stepwise.

6 is a three-dimensional graph showing the correlation between the city average effective pressure and DP _deg and CA _DP10 .

7 and 8 are two-dimensional graphs showing the correlation between the urban mean effective pressure and CA _{DP10 and} the correlation between the urban mean effective pressure and DP _deg , respectively.

FIG. 9 is a graph showing correction of the graph shown in FIG. 4 using the method of estimating the average urban effective pressure according to the present invention.

10 is a photograph of a diesel engine used to verify the present invention.

Claims (3)

A method for estimating the mean mean effective pressure inside a cylinder for an internal combustion engine comprising a cylinder and a piston reciprocating linearly in the cylinder, At the position where the crank connected to the piston is further rotated by a preset reference angle from the reference rotation position at the top dead center position of the piston, the actual pressure inside the cylinder and the reference angle before the crank is positioned at the reference rotation position. Measuring the actual pressure inside the cylinder at the less rotated position to obtain the difference in the measured pressures; Measuring an angle of the crank when the difference between the actual pressure inside the cylinder and the motoring pressure inside the cylinder becomes a preset reference pressure; And Estimating the urban mean effective pressure in the cylinder using the pressure difference in the cylinder and the measured crank angle. The method of claim 1, In the estimating step of the average urban effective pressure, the average urban effective pressure estimation method of the internal combustion engine, characterized in that for estimating by the following equation. Equation

here,

Is the estimated city average effective pressure, x and y are the pressure difference inside the cylinder and the measured crank angle, respectively, and a, b, c, d, e and f are determined by nonlinear curve fitting. The constant to be determined. The method according to claim 1 or 2, The reference angle is 60 degrees, the reference pressure is an urban average effective pressure estimation method of the internal combustion engine, characterized in that 10 bar (bar).

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