JP2830011B2 - How to create a combustion control map - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a method for creating a combustion control map, which aims at automation and improvement of the creation accuracy.

<Related Art> In recent years, many spark ignition internal combustion engines such as gasoline engines have been electronically controlled in response to demands for fuel saving and low pollution. Control forms include ignition timing control, knocking control, and fuel injection control.
ECU (Electronic C)
The mainstream is the one that performs intensive operations on an ontrol unit, and high reliability and low cost have been realized in conjunction with advances in semiconductor devices.

By the way, in the various controls described above, in many cases, a method is adopted in which information from the measuring means is processed by a combustion control map (hereinafter, a map) in a ROM or a RAM to determine a control amount. The map includes a two-dimensional map in which input values and output values correspond one-to-one, such as a temperature correction map,
There are three-dimensional maps corresponding to two types of parameters, such as a map for obtaining a fuel injection amount from an engine speed and an intake pressure.

These maps are generally obtained by performing experiments. For example, when an ignition timing map is created, the ignition timing is gradually advanced with the air-fuel ratio, the engine speed, the intake pressure, etc. fixed, and the MBT (Minimum
um Spark Advance for Best Torque) and find the optimal ignition timing that does not lead to knocking. Next, parameters such as the air-fuel ratio and the engine speed are changed, and the optimum ignition timing under the conditions is determined. Hereinafter, by repeating this experiment, maps corresponding to various driving states can be obtained.

<Problems to be Solved by the Invention> As is well known, the MBT, which is the ignition timing at which the maximum torque can be extracted from the engine, is near the ignition timing at which knocking occurs. On the other hand, the MBT detection operation requires a large measuring instrument such as a chassis dynamometer, and the operation itself is difficult because the detection of a delicate value is difficult.

For this reason, when creating an ignition timing map, a method is employed in which knocking due to advancing angle is detected instead of detecting an actual MBT, and a position shifted by a predetermined amount therefrom is regarded as an optimum ignition timing. And A / F (air-fuel ratio)
Other combustion control maps, such as maps, have been created in the same manner as the ignition timing map.

Knocking is a phenomenon in which the air-fuel mixture in the unburned part during combustion is self-ignited and temporarily burns without waiting for the propagation of the fire due to temperature rise due to adiabatic compression, etc., and combustion at this time occurs rapidly Therefore, pressure and temperature rise rapidly in the combustion chamber and a shock wave is generated. Therefore, at the time of creating the map, a skilled measurement person listened to the impact sound of the shock wave to determine knocking.

However, when such a method relying on the sense of hearing is adopted, since it takes time to perform each measurement, the number of measurements has to be reduced, and a detailed map cannot be created. In addition, while the measurement staff had to work in a power test room where the environment was poor, there were hygiene and safety problems, but there were many erroneous measurements due to the unskilledness of the measurement staff. In addition, due to knocking at each measurement, mechanical vibrations and distortions occur in each part of the test engine, and ignition plugs and pistons are easily overheated and melted. It took.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a method for creating a map without causing knocking, thereby enabling automation and speeding up of a test, and solving the above-mentioned problems.

<Means for Solving the Problems> The chemical reaction of normal combustion in a spark ignition internal combustion engine is
The reaction is performed through a first stage peroxide reaction, a second stage cool flame reaction (or formaldehyde reaction), and a third stage hot flame reaction. The cause explosive reaction in this step is the third step, first, second stage the precursor reaction hydrocarbon in the fuel formaldehyde or OH, is decomposed to high energy free radicals such as HO ₂ It is. In the vicinity of the MBT, that is, the knocking occurrence condition, the first and second stage precursor reactions are progressing in the unburned region in the combustion chamber at the pressure and temperature just before the self-ignition, and there are many free radicals with high energy, It is in a more chemically activated state than usual. Therefore, when the flame surface reaches there, the third stage of the flame reaction occurs immediately without delay required for the precursor reaction, and the flame speed and, consequently, the heat generation rate increase.

On the other hand, in the state where the heat generation rate is high, the combustion reaction is rapidly progressing, so that the physical quantity related to combustion, that is, the physical quantity of combustion changes naturally as compared with the normal state. For example, the internal pressure of a combustion chamber (hereinafter, cylinder pressure), which is one of the physical quantities of combustion, increases with combustion, but the rate of increase increases as the heat generation rate increases. Therefore, it is possible to calculate the change in the heat release rate from the change in the in-cylinder pressure, and by observing the change, it is possible to know whether or not the engine is near the knocking occurrence condition. .

Based on the above findings, the present invention is directed to a method for creating a combustion control map of a spark ignition internal combustion engine in order to solve the above-mentioned problems, wherein an in-cylinder pressure that varies with combustion in a combustion chamber of the spark ignition internal combustion engine. A combustion control map creation method is proposed in which a change state of the heat release rate is calculated from the above, a state immediately before knocking is detected based on the change state, and operating conditions at that time are used as parameters of the combustion control map. Is what you do.

<Operation> The test engine is operated while appropriately changing the operating conditions, and at the same time, the in-cylinder pressure is detected by a sensor or the like. Then, the detection signal is sent to the arithmetic unit to calculate a change state of the heat release rate, the change state is compared with a change state immediately before knocking stored in advance, and the operating condition is determined according to the comparison result. The result of the quantitative correction is stored as a parameter. This work is performed under various assumed operating conditions, and a combustion control map is created using the obtained parameters.

<Example> An example of the present invention will be specifically described with reference to the drawings.

FIG. 1 shows a schematic configuration of an ignition timing map creating device that creates an ignition timing map, which is one of the combustion control maps, using an in-cylinder pressure as a physical combustion quantity. Also, the second
The figure shows the relationship between the crank angle and the heat release rate. FIG. 3 shows a control flowchart in the present embodiment, and FIG. 4 shows an example of an ignition timing map created by the ignition timing map creating apparatus.

As shown in FIG. 1, an ignition timing map creation device according to the present embodiment includes a test four-cycle four-cylinder spark ignition internal combustion engine (hereinafter, referred to as an engine) 1 and an operation controller 2 for controlling an operation state of the engine 1. And an arithmetic unit 3 for performing arithmetic processing on the data obtained by the operation to create a map.

The combustion chamber 4 of each cylinder of the engine 1 is provided with an in-cylinder pressure sensor 6 as an in-cylinder pressure detecting means in addition to the ignition plug 5. The in-cylinder pressure sensor 6 incorporates a piezoelectric element.
The pressure in the cylinder is converted into electric charges and output. A crank angle sensor 8 is provided adjacent to the flywheel 7, and an intake pressure sensor 11 for detecting intake pressure and an oxygen concentration in exhaust gas are respectively provided on an intake pipe 9 and an exhaust pipe 10. and O ₂ sensor 12 is attached. The crankshaft 13 is connected to a dynamometer 14 for applying a load to the engine 1 and measuring output, shaft torque, and the like.

The operation controller 2 drives the spark plug 5 via an ignition driver or the like, and also controls a fuel injection valve, a throttle valve, and the like (not shown) to control an injection amount, an intake amount, and the like.

The measured values measured by the sensors and the dynamometer 14 and the control values of the operation controller 2 are all input to the arithmetic unit 3. In the arithmetic unit 3, the signal from the in-cylinder pressure sensor 6 is input to the heat generation pattern arithmetic unit 15 together with the signal from the crank angle sensor 8, and after the processing is performed, RA
Input to M16. The signal from the crank angle sensor 8 is sent to the O ₂ sensor 12 via the engine speed calculation unit 17.
From the RAM 1
Enter 6 Then, signals from other sensors and devices are directly input to the RAM 16. In addition to the sensors and devices described above, the arithmetic unit 3 is connected to detection means (not shown) for detecting atmospheric conditions such as atmospheric pressure and atmospheric temperature. A signal from the detection means is also input to the RAM 16.

The arithmetic unit 3 further includes a data bank 19, an optimal ignition timing arithmetic unit 20, and a map creating unit 21. The data input from the heat generation pattern calculation unit 15 to the RAM 16 is input to the data bank 19 via the optimum ignition timing calculation unit 20. Further, various other signals (data) in the RAM 16 are also arranged and input to the data bank 19. The map creation unit 21 creates an ignition timing map using each data in the data bank 19.

Hereinafter, the operation of this embodiment will be described with reference to the flowchart of FIG.

Is activated on the operation controller 2, in the engine 1 starts to rotate, before the arithmetic unit 3 test, the minimum frequency of the engine rotational speed N _E at the start of the test (idling),
The load L is set to no load, the air-fuel ratio A / F is set to the maximum rich, and the ignition timing S is set to the maximum retard value.

Then, the actual engine speed N _E by the crank angle sensor 8, a throttle position sensor, the actual load L by the output of such intake pressure sensor, O ₂ sensor 12 the actual air-fuel ratio A / F by is measured respectively , Is compared with the set value in the arithmetic unit. When there is a difference between the measured value and the set value, a correction amount for the set value is calculated so as to eliminate the difference, and is input to the operation controller 2.

When the set value and the measured value become equal, i = 1, and the crank angle θ is set by the crank angle sensor to the in-cylinder pressure sensor 6.
, The in-cylinder pressure P of each cylinder is detected. And
The heat generation pattern calculation unit 15 calculates the heat generation rate dQ / dθ by using the crank angle θ and the in-cylinder pressure P in the following procedure.

First, as shown below, the heat release amount dQ and the internal energy increment
An operation is performed using each operation expression for obtaining du and a state equation.

Here, G is the amount of combustion gas, A is the heat equivalent of work, R is the gas constant, Cv is the specific heat of constant volume, k is the ratio of the specific heat, and T is the absolute temperature.

From equations (1), (2) and (3) Therefore, the heat release rate (dQ / dθ) is as follows.

At this time, in the combustion stroke (top dead center to 50 ° after top dead center) Therefore, the above equation may be approximated as follows.

That is, the heat release rate can be approximated by the rate of change of the in-cylinder pressure.

When calculating the heat generation rate as described above, it is desirable to cut a high-frequency vibration component due to knocking or the like with a filter. In other words, a high-frequency vibration component is always superimposed on the acupressure diagram, and by cutting this vibration component, the change state of the heat generation rate is simplified as shown in FIG. Therefore, in this embodiment, the low-pass filter 2 using the direct FFT method or the spline function method is used.
2 is used.

Next, the heat generation pattern calculation unit 15 calculates the heat generation rate dQ / dθ from the obtained heat generation rate dQ / dθ (or the rate of change of the in-cylinder pressure dP / dθ... d
The time required for the fall of θ, that is, the transition time from the maximum value to the completion of combustion is calculated. As the transition time, not the real time, but the difference | θ ₁₀₀ −θ ₀ | between the crank angle θ _{100 at} the maximum value and the crank angle θ ₀ at the completion of combustion is used.

 Subsequently, the output torque T of the engine is detected.

Then, the engine speed N _E , load L, and air-fuel ratio at that time
A / F, ignition timing S, transition time | θ ₁₀₀ −θ ₀ |, torque T
Is stored in the RAM, and it is determined whether i = 100.

If i is less than 100, the engine speed _NE , load L, air-fuel ratio A / F, ignition timing S, transition timing | θ ₁₀₀ −θ ₀ | and torque T are calculated or detected again as i−i + 1, and RAM
To memorize.

Then, when i = 100, data out of the permissible variation range is deleted from the 100 data stored in the RAM. Specifically, of the 100 times of data, data in which any one of the rotational speed _NE , the load L, the air-fuel ratio A / F, and the ignition timing S has an extremely different value from the set value is deleted.

Next, the above-mentioned transition time | θ ₁₀₀ −θ ₀ | is compared with an absolute set value described later, and it is determined whether or not the knocking state is established by the following method.

That is, as shown in FIG. 2, the heat release rate (shown by a solid line) in the state immediately before knocking changes greatly in the way of falling compared to the state before that (shown by a broken line), and the transition time | θ
₁₀₀ −θ ₀ | is shorter. Therefore, if the transition time | θ ₁₀₀ −θ ₀ | immediately before knocking is set as an absolute setting value,
It is possible to determine whether or not the vehicle is in a knocking state.

In FIG. 2, the crank angle θ ₀ is the time when the combustion is completed. Since the combustion is completed, no new heat is generated, and the heat release rate dQ / dθ is naturally 0, as described above. ,
The rate of change of the in-cylinder pressure can also be approximated.

Then, the transition time | θ ₁₀₀ -θ ₀ | calculates the establishment A ₁ which is smaller than the absolute setting value, compares it with the allowable value A _0.
Here, A ₀ is a determination reference value of the knock margin, which determines that there is no margin for knock in the case of A ₁ <A ₀ Dearebajubun'nokkushinaijotaidearutohanteishi,A _1> A ₀ It is.

If A ₁ <A ₀ , the MBT is determined.

That is, the average value T of the torque T at the time of the previous data acquisition.
and _n-1, the average value T _n of the torque T at the time of the current data capture
Comparing the door, the comparison result is a MBT the preceding ignition timing when changed from T _n ≧ T _n-1 to T _n <T _n-1.

If T _n ≧ T _n-1 , the current transition time | θ ₁₀₀ −
The deviation between the average value B ₁ of θ ₀ | and the reference value B ₀ is determined. here,
The reference value B ₀ is for determining whether or not the ignition timing S can be further advanced. The knock margin due to the probability A ₁ that the above-mentioned transition time | θ ₁₀₀ −θ ₀ | becomes smaller than the absolute set value is determined. This is to determine the advance angle limit with higher accuracy than the determination. Then, B ₁ and variance b ₁ of B ₀ is allowable value b ₀ or more than dX ° advances the ignition timing S if hidden again performs 100 times of data acquisition described above.

On the other hand, the deviation b ₁ of B ₁ and B ₀ is equal tolerance b ₀ or less, it is determined that the operating parameter is an optimal value at that time, and stores the respective values in the RAM as the MAP data. That is, when the advance angle limit comes before the MBT, the advance angle is interrupted at that time.

Also, if a T _n <T _n-1 in the determination of the maximum torque of the foregoing, it is determined that there was want to Incidentally movement angle past the MBT, and dX ° retarding the ignition timing S, each Operating parameters MA
Store as P data in RAM.

As described above, when the optimum ignition time S when the engine speed _NE is the minimum engine speed (idling), the load L is no load, and the air-fuel ratio A / F is the maximum rich is obtained, the rotational speed N _E to the minimum rotational speed (idling), while the load L was fixed to no load, to lean by dY than the maximum rich the air-fuel ratio a / F, respectively a
The optimum ignition timing S at the / F value is obtained.

Then, when the optimum ignition timing S for each A / F value from the highest rich to the lean limit value is obtained, the value of the load L is changed and data is fetched. That is, the minimum rotation speed of the engine rotational speed N _E (idling)
Next, the load L is fixed to a value increased by dL from the no load, and the optimum ignition timing S for all A / F values is obtained.

Thereafter, the load L is increased by dL to the maximum load,
For each load value, the A / F value is changed from the highest rich to the lean limit value, and the optimum ignition timing S is obtained. Then, the minimum rotational speed of the engine rotational speed N _E,
When the optimal ignition timing S for all combinations of the load L and the A / F value is obtained, the engine speed is changed and the data is acquired. In other words, gradually increasing the engine speed from the minimum rotational speed by dN _E until the maximum rotational speed, for each of the rotational speed by changing the load L and A / F value, determining the optimum ignition timing with respect to all setting values.

As described above, the optimum ignition timing S for all combinations from the initial value to the limit value for the engine speed _NE , the load L, and the air-fuel ratio A / F is obtained. It is input to bank 19.

Next, the data in the data bank 19 is compiled into a measurement data group shown in FIGS. Finally, the combination of the optimum ignition timing and the air-fuel ratio is extracted and arranged by the map creation unit 21 according to the type of the vehicle on which the engine is mounted (fuel efficiency or output). An ignition timing map as shown in FIG. 4 is created.

Although the description of the embodiment has been finished above, the present invention is not limited to this embodiment. For example, in determining whether or not knocking conditions are near, a heat generation rate of 50% with respect to the maximum value of the heat generation rate is determined. it may be other regions such as in the range of up to crank angle theta ₁₀ showing a 10% heat generation rate from the crank angle theta ₅₀ showing the incidence. Further, the present invention is not used only for preparing the ignition timing and the air-fuel ratio map, but is based on the measured data groups such as the EGR rate and the supercharging pressure shown in FIGS. 7 and 8, respectively.
You may apply to the combustion control map preparation apparatus which produces each map.

<Effect of the Invention> According to the combustion control map creating method of the present invention, the state immediately before knocking is detected from the change in the in-cylinder pressure, and the operating condition at that time is used as a parameter of the combustion control map. The creation of the combustion control map, which relied on the hearing of the members, is automated, and a detailed and accurate combustion control map can be created in a short time. Further, since it is not necessary to generate knocking in creating the combustion control map, the life of the test engine is improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing an ignition timing map creation device according to one embodiment of a combustion control map creation method of the present invention. FIG. 2 is a graph showing the relationship between the crank angle and the heat release rate. FIG. 3 is a control flowchart of the ignition timing map creator of this embodiment, and FIG. 4 is an ignition timing map created by the ignition timing map creator of this embodiment. FIGS. 5 to 8 show data groups for creating an ignition timing map, an air-fuel ratio map, an EGR rate map, and a supercharging pressure map. In the figure, 1 is an engine, 2 is an operation controller, 3 is an arithmetic unit,
6-cylinder pressure sensor, a crank angle sensor 8, the intake pressure sensor 11, the O ₂ sensor 12, 14 is dynamometer, 15 heat generation pattern calculation unit, 16 RAM, 17 is an engine rotational speed calculation unit, 19 Is a data bank, 20 is an optimal ignition timing calculation unit, and 21 is a map creation unit.

──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Hiromitsu Ando 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Inventor Daisuke Mibayashi 5-33-8 Shiba, Minato-ku, Tokyo No. Mitsubishi Motors Corporation (56) References JP-A-62-130330 (JP, A) JP-A-54-112 (JP, A) JP-A-59-136544 (JP, A) JP-A-64 -19174 (JP, A) JP-A-59-136543 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) F02D 45/00

Claims (1)

(57) [Claims] 1. A method for preparing a combustion control map of a spark ignition internal combustion engine, comprising calculating a change state of a heat generation rate from an in-cylinder pressure that changes with combustion in a combustion chamber of the spark ignition internal combustion engine. A method for creating a combustion control map, comprising detecting a state immediately before knocking based on a change state of a heat release rate and using operating conditions at that time as parameters of a combustion control map.