JPH02221662A - Method of forming combustion control map - Google Patents

Abstract

PURPOSE:To automize the formation of a map and shortening the time thereof by calculating the changing state of heat generating rate from a combustion physical quantity changed according to the combustion in a combustion chamber to detect the state just before knocking, and using the operating condition at that time as a parameter of combustion control map. CONSTITUTION:When an engine 1 is rotated, engine speed NE, load L, and air-fuel ratio A/F are measured by a crank angle sensor 8, the output of an intake pressure sensor 11, and an O2 sensor 12, respectively. When the measured values are equal to respective set values compared therewith in an arithmetic device 3, crank angle theta and cylinder internal pressure P of each cylinder are detected by the crank angle sensor 8 and a cylinder internal pressure sensor 6, respectively, and heat generating rate dQ/dtheta is calculated by a heat generating pattern calculating unit 15. Then, the state just before knocking is detected from the changing state of this heat generating rate dQ/dtheta. The operating condition at that time is used as a parameter of combustion control map, and an ignition time map is formed by a map forming unit 21.

Description

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

<Conventional technology> In recent years, spark ignition internal combustion engines such as gasoline engines have
In response to demands for fuel efficiency and low pollution, more and more devices are becoming electronically controlled. The form of control is mainly fuel injection control, ignition timing control, knocking control, idle speed control, EGR control, etc.
It has become mainstream to carry out the process intensively using a ronic control unit (8), and combined with advances in semiconductor devices, high reliability and cost reduction have been achieved.

By the way, in the above-mentioned container control, in many cases, information from the measuring means is stored in the combustion control map (ROM or RAM).
A method is adopted in which the control amount is determined by processing using a map (hereinafter referred to as map). Maps include two-dimensional maps that have a one-to-one correspondence between input values and output values, such as concentration correction maps, and maps that have two types of parameters, such as maps that calculate fuel injection amount from engine speed and intake pressure. There is a corresponding three-dimensional map.

These maps are generally obtained by conducting experiments. For example, when creating an ignition timing map, the ignition timing is gradually advanced while the air-fuel ratio, engine speed, intake pressure, etc. are fixed, and M B T
(Minimum Spark Advance for
Find the optimal ignition timing that is near the engine speed (Be5t Torque) and does not cause knocking. Next, change parameters such as the air-fuel ratio and engine speed, and find the optimal ignition timing under those conditions. By repeating this experiment, maps corresponding to various operating conditions can be obtained.

<Problems to be Solved by the Invention> As is well known, the MBT, which is the ignition timing that can extract the maximum torque from the engine, is near the peak timing at which knocking occurs. On the other hand, MBT detection work requires large measuring equipment such as a Petri dynamometer, and the work itself is difficult because it involves detecting delicate values.

Therefore, when creating an ignition timing map, rather than detecting the actual MBT, wait for knocking to occur due to advance angle, and then set the position shifted by a predetermined amount from there! & A method of determining the appropriate ignition timing was adopted. Other combustion control maps such as A/F (air-fuel ratio) maps were also created in the same manner as the ignition timing map.

Knocking is a phenomenon in which the unburned air-fuel mixture during combustion self-ignites without waiting for flame propagation due to temperature rise due to adiabatic compression, resulting in temporary combustion.In this case, combustion occurs rapidly. As a result, pressure and temperature rise rapidly within the combustion chamber, and a shock wave is generated.

Therefore, when creating a map, skilled measurement staff listens to the knocking sound caused by shock waves and determines knocking.

However, when such a method relying on auditory sensation is adopted, it takes time to make each measurement, so the number of measurements has to be reduced, and a detailed map cannot be created.

In addition, the measurement staff had to work in a power testing room with poor environmental conditions, which caused health and safety problems, and there were also many measurement errors due to lack of skill on the part of the measurement staff. Furthermore, because knocking occurs every time a measurement is made, mechanical vibrations and distortions occur in various parts of the test engine, and spark plugs and pistons are prone to overheating and melting, which shortens the engine's lifespan. It took.

The present invention was made in view of the above-mentioned situation, and aims to solve the above-mentioned problems by providing a method for creating a map without causing knocking, thereby making it possible to automate and speed up testing.

<Means for solving am> The chemical reactions of normal combustion in a spark-ignition internal combustion engine include a peroxide reaction in the first stage, a cold flame reaction (or formaldehyde reaction) in the second stage, and a hot flame reaction in the third stage. Go through each step of the reaction.

Among these stages, it is the third stage that causes an explosive reaction.
1st. The second stage is a precursor reaction in which the hydrocarbons in the fuel range are decomposed into high-energy free radicals such as formaldehyde, OH, and HO2J.

Near MBT, that is, knocking conditions, the first ignition occurs in the unburned region of the combustion chamber where the pressure and temperature are on the verge of self-ignition. The second stage precursor reaction is in progress, with many high-energy free radicals and usually in a chemically activated state. Therefore, when the flame front reaches there, the third stage hot flame reaction occurs immediately without the delay required for the precursor reaction, and the flame speed and thus the heat release rate increase.

On the other hand, in a state where the heat release rate is high, the combustion reaction is progressing rapidly, so naturally the physical quantities related to combustion, that is, the physical quantities of combustion, change compared to normal times.For example, one of the physical quantities of combustion The internal pressure of the combustion chamber (hereinafter referred to as cylinder pressure) increases as combustion occurs, and the rate of increase increases as the heat release rate increases.In addition, as another physical quantity of combustion, the combustion light obtained from the fire when fuel burns These include strength, but these also change with the heat release rate.Therefore, it is possible to calculate the heat release rate or the physical change state that is correlated with the heat release rate from the change state of these physical quantities of combustion. By observing the changes, it is possible to know whether or not the engine is close to the conditions where knocking occurs.

Based on the above knowledge, in order to solve the above-mentioned problems, the present invention provides a method for creating a combustion control map for a spark-ignition internal combustion engine, which includes combustion physical quantities that change with combustion in a combustion chamber of the spark-ignition internal combustion engine. Calculate the heat release rate and changes in physical quantities that are correlated with the heat release rate, detect the state on the verge of knocking based on this change, and use the operating conditions at that time as parameters for the combustion control map. This paper proposes a combustion control map creation method featuring the following features.

Effect〉 Operate the test engine while changing the operating conditions as appropriate,
At the same time, physical quantities of combustion are detected using sensors, etc. This detection signal is then sent to a calculation device to calculate the change status of the heat release rate or a physical quantity correlated with this, and the change status is compared with a pre-stored change status on the verge of knocking. According to the results, the operating conditions plus a predetermined company's correction are stored as parameters. This work is performed under various assumed operating conditions, and a combustion control map is created using each of the obtained parameters.

Example of implementation An embodiment of the present invention will be specifically described based on the drawings.

FIG. 1 shows a schematic configuration of an ignition timing map creation device that creates an ignition timing map, which is one of the combustion control maps, using cylinder pressure, which is a physical quantity of combustion. Further, FIG. 2 shows the relationship between crank angle and heat generation rate. FIG. 3 shows a control flowchart in this embodiment.
FIG. 4 shows an example of an ignition timing map created by the ignition timing map creation device.

As shown in FIG. 1, the ignition timing map creation device of this embodiment includes a test 4-cycle 49F% cylinder spark ignition internal combustion engine (hereinafter referred to as engine) 1 and an operation controller that controls the operating state of this engine 1. 2, and an arithmetic unit 3 that processes data obtained through operation to create a map.

In addition to the spark plug 5, a cylinder pressure sensor 6 serving as a cylinder pressure detection means is attached to the combustion chamber 4 of each 9c cylinder of the engine 1. The cylinder pressure sensor 6 incorporates a piezoelectric element,
It converts the pressure inside the cylinder into electric charge and outputs it. Also, the flywheel 7 is equipped with a crank angle sensor 8 IIJ1f! Then set up and suck! ! An intake pressure sensor 11 for detecting the intake pressure and an 02 sensor 12 for detecting the oxygen concentration in the exhaust gas are attached to the exhaust gas w10 and the exhaust gas w10, respectively. A dynamometer 14 is connected to the crankshaft 13 for applying a load to the engine 1 and for measuring output, shaft torque, and the like.

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

All of the measured values measured by the above-mentioned sensors and dynamometer 14 and the control values of the operation controller 2 are input to the calculation device 3. In the calculation device 3, the signal from the cylinder pressure sensor 6 is input to the crank angle sensor 8. It is input to the heat generation pattern calculation unit 15 together with the signal, and after being processed, it is input to the RAM 16. Further, the signal from the crank angle sensor 8 is sent to 0 through the engine rotation speed calculation unit 17.
The signals from the two sensors 12 are amplified by the amplifier 18 and input to the RAM 16, respectively. Signals from other sensors and devices are input to the RAM 16 as they are. In addition to the above-mentioned sensors and devices, a detection means (not shown) for detecting atmospheric conditions such as atmospheric pressure and temperature is connected to the arithmetic unit 3, and signals from the detection means are also input to the RAM 16.

Further provided within the calculated value M3 are a data bank 19, an optimum ignition timing calculation unit 20, and a map creation unit 21. RA from heat generation pattern calculation unit 15
The data input to M16 is sent to the optimum ignition timing calculation unit 2.
0 to the data bank 19.

Further, various other signals (data) in the RAM 16 are also organized 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.

The operation of this embodiment will be described below based on the flowchart of FIG.

When the engine 1 is activated by the operation controller 2 and starts rotating, the arithmetic unit 3 sets the engine rotation speed N6 at the start of the test to the minimum rotation speed (idling) prior to the test.
The load is set to no load, the air-fuel ratio A/F is set to the richest value, and the ignition timing S is set to the maximum retard value, and these are input to the controller 2.

Next, the crank angle sensor 8 detects the actual engine speed NI! However, the actual load is measured by the outputs of the throttle position sensor, intake pressure sensor, etc., and the actual air-fuel ratio A/F is measured by the 02 sensor 12, and these are compared with the set values in the arithmetic unit. If there is a difference between the measured value and the set value, a correction amount for the set value is calculated so that there is no 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 sensor detects the crank angle θ, and the cylinder pressure sensor 6 detects the cylinder pressure P of each cylinder. Then, the heat release pattern calculation unit 15 calculates the heat release rate r using the crank angle θQ and the cylinder pressure P according to the following procedure.

First, as described below, calculations are performed using various calculation formulas and state equations for determining the amount of heat generation dQ and the internal energy increment du.

dQ=G −d u+A −P −dV −(1)
du=cv-dT=”'-dT -(21 to -1 PV=G-R-T ・+31 However, G is the amount of combustion gas, A is the heat equivalent of work, R is the gas constant, and Cv is the constant volume specific heat. , k is the ratio of specific heats, and T is the absolute temperature.

(11# (21, (From formula 31, -A-R dQ=dT+A-P·dV) Therefore, the heat generation rate (dQ/dθ) is as follows.

In this case, the combustion stroke (from top dead center to after top dead center) may be approximated.

In other words, the heat release rate can be approximated by the rate of change in cylinder pressure.

Note that when calculating the heat release rate as described above, it is desirable to use a filter to cut out high-frequency vibration components due to knocking or the like. In other words, a high-frequency vibration component is always superimposed on the acupressure diagram, and by cutting this vibration component, the state of change in the heat release rate can be simplified as shown in FIG. 1. Therefore, in this embodiment, a low-pass filter 22 using a direct FFT method or a spline function method is used.

Next, in the heat generation pattern calculation unit 15, the obtained heat generation rate - dQ (or the rate of change in the cylinder pressure d θ dP dQ -.
・The time required for the heat release rate da to fall, that is, the transition time from its maximum value to the completion of combustion, is calculated from the heat release rate d θ dQ (hereinafter represented by the heat release rate ae). This transition time is not actual time, but the crank angle θ1° at the maximum value. and the crank angle θ at the completion of combustion. The difference between them is 1θ1°. −〇. 1 is used.

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

And the engine speed Nl at that time! , load L1 air-fuel ratio A/F, ignition timing S1 transition time θ1°. −θ. 1. Store torque T in RAM and determine whether 1=100.

If i is less than 100, i −i + 1 is again set as engine speed N1, load L1, air-fuel ratio A/F1, ignition timing S, and transition timing 1 θ1°. −θ.

Calculate or detect torque T and store it in RAM.

Then, when i -100 is reached, data outside the allowable variation range out of the 100 data stored in INAM is deleted. Specifically, out of 100 data, rotation speed N6
, load L1 air-fuel ratio A/F, and ignition timing S are deleted.

Next, the aforementioned transition time 1 θ,. . −〇. 1 and an absolute set value, which will be described later, and determine whether or not there is a knocking state using the method described below.

That is, as shown in Fig. 2, the heat release rate (indicated by a solid line) in a state on the verge of knocking has a steeper fall (changes) than in the state before that (indicated by a broken line), and the transition time 1 θ1
゜. −〇. 1 is shorter. Therefore, the transition time just before knocking is 1 θ1°. −〇. By setting 1 as an absolute setting value, it is possible to determine whether or not a knocking condition is occurring.

Next, the transition time is 1 θ1°. −〇. The probability A1 that 1 is smaller than the absolute setting value is calculated, and this is set as the tolerance value A. Compare with. Here, Ao is the criterion value for knock margin,
If A, < Ao, it is determined that there is sufficient knocking, and if A, > Ao, it is determined that there is no margin for knocking.

If A1<Ao, the MBT is determined.

That is, the average value T of the torque T at the time of the previous data acquisition.

−1 and the average value T of torque T at the time of data acquisition this time
. and the comparison result is T, ≧Tn-, to T, , <
T. Let the previous ignition timing when the timing changes to 4 be MBT.

If T,≧T,, the current transition time 1 θ,
. . −〇. The deviation between the average value B of 1 and the reference value B0 is determined. Here, the reference value B0 is used to determine whether or not the ignition timing S can be roughly advanced, and the above-mentioned transition time 1 θ.

. −〇. The probability A that 1 is smaller than the absolute setting value is used to determine the advance angle limit with higher accuracy than the determination of the knock margin. Then, B, and the deviation b1 of 80
is an acceptable value. If it is above, advance the ignition timing S by dX',
The data acquisition described above is performed again 100 times.

Meanwhile, B and B. If the deviation S is less than or equal to the allowable value b0, it is determined that the operating parameters at that time are the optimum values, and the respective values are stored in the RAM as MAP data. That is, if the advance angle limit is reached before the MBT, the advance angle is interrupted at that point.

In addition, if T, , < T, , -1 is obtained in the above-mentioned maximum torque judgment, it is determined that the ignition timing is still advanced past the MBT, and the ignition timing S is retarded by dX'. , each operating parameter is stored in the RAM as MAP data.

In the above manner, the engine rotation speed N is set to the minimum rotation speed (
After determining the optimal ignition time Hs when the load is at the maximum (idling), no load, and the air-fuel ratio A/F is at its maximum richness, next, set the engine speed N6 to the minimum speed (idling) and no load. While each load is fixed, the air-fuel ratio A/F'eR is made lean by dY from high rich to find the optimum ignition timing S at each A/F value.

Once the optimum ignition timing S for each A/F value from the maximum rich to the lean limit value has been determined, the load value is then changed and data is acquired. That is, the engine speed NE is fixed at the minimum speed (idling) and the load is fixed at a value increased by dL from the no-load value, and the optimum ignition timing S for all A/F values is determined.

After that, increase the load by dL until the maximum load,
For each load value, the maximum ignition timing S is determined by changing the A/F value from the maximum rich to the lean limit value. And engine speed Nl! Once the optimum ignition timing MS for all combinations of load and A/F value has been obtained for the lowest engine speed, the engine speed is changed and data is captured.

That is, the engine speed is increased by dNl! from the minimum rotation speed to the maximum rotation speed! The load and A/F value are changed for each rotation speed, and the Ra ignition timing for all set values is determined.

In the above manner, the optimum ignition timing S for all combinations of engine speed N6, load, and air-fuel ratio A/F from the respective initial values to the limit values is determined, and the obtained data is stored in the data bank from the RAM 16. 19 is input.

Next, the data in the data bank 19 is edited into a measurement data group shown in FIG. Finally, the map creation unit 21 extracts and organizes the combinations of optimal ignition timing and air-fuel ratio according to the type of vehicle in which the engine is installed (e.g. whether the emphasis is on fuel economy or output), and the combinations of optimal ignition timing and air-fuel ratio are extracted and organized from these optimal ignition timing data. An ignition timing map as shown in Figure 4 is created.

This concludes the explanation of the embodiment, but the present invention is not limited to this embodiment. For example, in determining whether or not the knocking generation condition is near, 10% from crank angle θ6° showing the heat release rate of
The crank angle θ, which indicates the heat release rate. It is also possible to use other ranges, such as the range up to , or to use the above-mentioned combustion light intensity instead of the in-cylinder pressure as the combustion physical quantity.

Furthermore, the present invention is not only used to create ignition timing and air-fuel ratio maps, but also to create each map from a group of measurement data such as EGR rate and boost pressure shown in FIGS. 7 and 8, respectively. It may also be applied to a combustion control map creation device.

<Effects of the Invention> Combustion fIjlJIj of the present invention! According to the a-map creation method, a state on the verge of knocking is detected from changes in combustion physical quantities, and the operating conditions at that time are used as parameters for the combustion control map. The creation of combustion control maps, which previously relied on intuition, has been automated, making it possible to create detailed and accurate combustion control maps in a short time. Furthermore, since there is no need to generate knocking when creating a combustion control map, the life of the test engine is extended.

[Brief explanation of the drawing]

FIG. 1 is a schematic configuration diagram showing an ignition timing map creation device according to an embodiment of the combustion control map creation method of the present invention. Further, FIG. 2 is a graph showing the relationship between crank angle and heat generation rate. FIG. 3 is a control flowchart of the ignition timing map creation device of this embodiment, and FIG. 4 is an ignition timing map created by the ignition timing map creation device of this embodiment. Furthermore, FIGS. 5 to 8 are data groups for creating an ignition timing map, an air-fuel ratio map, an EGR rate map, and a supercharging pressure map, respectively. In the figure, 1 is the engine, 2 is the operation controller, 3 is the computing device, 6 is the cylinder pressure sensor, 8C is the rank angle sensor, 11 is the intake pressure sensor, 12 is the heel sensor, 14 is the dynamometer, and 15 is the heat generation pattern. Arithmetic unit, 16 is RAM. 17 is an engine speed calculation unit, 19 is a data bank, 20 is a J[I ignition timing calculation unit, and 21 is a map creation unit.

Claims (2)

[Claims] (1) A method for creating a combustion control map for a spark-ignition internal combustion engine, which calculates changes in the heat release rate from combustion physical quantities that change with combustion in the combustion chamber of the spark-ignition internal combustion engine, and A method for creating a combustion control map, characterized in that a state on the verge of knocking is detected based on a rate change, and the operating conditions at that time are used as parameters of the combustion control map. (2) A method for creating a combustion control map for a spark-ignition internal combustion engine, which calculates changes in physical quantities that are correlated with the heat release rate from combustion physical quantities that change with combustion in the combustion chamber of the spark-ignition internal combustion engine. A method for creating a combustion control map, characterized in that a state on the verge of knocking is detected based on the state of change in this physical quantity, and the operating conditions at that time are used as parameters of the combustion control map.