JPS6168533A - Detection of max. combustion pressure generation timing for internal combustion engine - Google Patents

Abstract

PURPOSE:To detect the max. combustion pressure generation timing, by checking the max. combustion pressure at a fixed cycle of an internal combustion engine and a pressure at the crank angle pitch before and after it to determine a proximate function of the combustion pressure with respect to the crank angle. CONSTITUTION:A combustion pressure sensor 3 and an ignition plug are provided at the top of a combustion chamber 2 of a cylinder 1 of an internal combustion engine and a distributor 6 and a crank angle sensor 7 are provided on a crank shaft connected to a piston 5. A combustion pressure detecting section 22 takes in a combustion pressure Pi from the sensor 3 synchronizing and corresponding to an angle thetai of crank inputted into an angle of crank detector section 21 to be memorized into a memory. A max. combustion pressure generation timing computing section 23 takes in the combustion pressure Pi from the detecting section 22 to retrieve the max. value PK while approximating changes in the combustion pressure P based on the detection values PK-1 and PK+1 before and after it in terms of function. The angle thetapmax of crank is determined corresponding to the max. value Pmax of the approximate function thus obtained is determined to be outputted to an ignition timing controller 30.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for detecting the maximum combustion pressure generation timing, which is necessary for ignition timing feedback control of an internal combustion engine.

[Conventional technology]

Generally, in an internal combustion engine, if the combustion pressure reaches its maximum when the crankshaft rotates a certain angle α from top dead center, that is, α'A', r'D C, the engine output will increase. It is known to reach the maximum.

The value of α is a characteristic value determined depending on the type of internal combustion engine, etc., and is usually around 15°.

Therefore, the maximum value Pmax of the cylinder pressure of the internal combustion engine is detected, and the crank angle θpmax at that time is
Feedback control is being carried out to detect θpmax and correct the ignition timing in order to make it coincide with αK. Conventionally, as a method for detecting Pmax and θpmax, a crank angle sensor that outputs a pulse signal at every fixed rotational displacement angle Δθ is provided in relation to the crankshaft, and the combustion pressure in the cylinder is adjusted in synchronization with the pulse signal. Detect P and set the maximum value of the detected combustion pressure as Pmax
and the crank angle θ at that time is θpmax
I was trying to do that.

[Problem that the invention seeks to solve]

Moreover, in the conventional maximum combustion pressure detection method, if the detection accuracy is to be improved, the detection interval of the combustion pressure P should be made closer, that is, the above value should be made small (for example, 05 to 1.
0°CA) If you increase the resolution and provide it, there will be many possibilities. However, when the detected values are processed by an arithmetic device such as a microcomputer, the higher the resolution, the higher the C.
There is a problem that the PU load increases. In addition, if 80 is made smaller, the crank angle sensor becomes larger, and there are limits to the structure, and Δθ was suppressed to 3 to 5 degrees CA.

An object of the present invention is to provide a maximum combustion pressure generation timing detection method for an internal combustion engine that can detect the maximum combustion pressure generation timing with high accuracy without increasing the combustion pressure detection interval.

[Means for solving problems]

In order to achieve the object F, the present invention detects the combustion pressure of an internal combustion engine at every predetermined crank angle pitch, and detects the maximum combustion pressure detection value in a certain period and the detection value at the crank angle pitch before and after the maximum value of the combustion pressure detection value in a certain period. Based on this, the change in combustion pressure with respect to the crank angle in the relevant period is approximated by a function, and the crank angle corresponding to the maximum value of this approximation function is set as the maximum combustion pressure generation time.

[Effect]

In other words, the present invention focuses on the fact that the combustion pressure of an internal combustion engine changes as a continuous curve, and that the change curve near the maximum value is approximately symmetrical around the crank angle of the maximum value. According to the present invention having the above configuration, a combustion pressure change curve is approximated as a function based on combustion pressure detection values at three points near the maximum value, and the maximum value of this approximation function is determined as a combustion pressure change curve. Since the maximum value is approximated, it is possible to detect the timing of the maximum combustion pressure with high accuracy without making the combustion pressure detection intervals too close.

〔Example〕

Hereinafter, the present invention will be explained based on examples.

FIG. 1 shows an overall schematic configuration diagram of an embodiment of an apparatus to which the present invention is applied.

As shown in FIG. 1, a combustion chamber 2 of a cylinder 1 of an internal combustion engine
A combustion pressure sensor 3 and a spark plug 4 are provided on the top of the engine. A distributor is provided to engage with a crankshaft (not shown) connected to the piston 5, and a crank angle sensor 7 is provided in association with the distributor 6.

In Fig. 1, 8 is an air filter, 9 is an air flow meter, 1o is a throttle valve, 11 is a fuel injection nozzle, 12 is an intake valve, 13 is an exhaust valve, and 14 is an exhaust process. This is a catalytic converter for.

The crank angle sensor 7 includes a crank reference position sensor that outputs a pulse signal BP every time the crankshaft rotates 7200 degrees, and a crank angle sensor that outputs a pulse signal CP at every fixed rank angle pitch (for example, 5° CA). It is formed by including. That is, the pulse signal BP is a reference signal representing two revolutions of the internal combustion engine, and the pulse signal CP is a clock pulse signal for detecting combustion pressure P, etc.

Which of the pulse signals BP and CP is inputted to the crank angle detection unit 211C of the maximum combustion pressure detection device [20] formed from a microcomputer, etc., where the waveform is shaped and the crank angle θ from the reference position is The crank angle θ4 (j-1, 2, 3, . . . ) representing the
It is designed to output to 2.

The combustion pressure detection unit 22 detects the combustion pressure Pi (i-1, 2°...) in synchronization and correspondence with the input crank angle θi.
...) from the combustion pressure sensor 3 and stores it therein.

The maximum combustion pressure generation timing calculation unit 23 is driven based on the pulse signal BP, and retrieves the combustion pressure Pl from the combustion pressure detection unit 22 to search for the maximum value Pk, and also detects the timing before and after the combustion pressure Pl. Value Pk −1, Pk+
Functional approximation of the change in combustion pressure P based on ttic,
Crank angle θ corresponding to the maximum value Pmax of this approximation function
pmax is determined and output to the ignition timing control device 30.

An example of this function approximation will now be described with reference to FIG. What is shown in FIG. In formulas (1,) and (2), a, b, c
is a constant.

P-aθ2+bθ+(! ・(1)
According to this quadratic function approximation, the combustion pressure change curve can be approximated with high precision, and the value of θpmax can be determined with high precision.

However, according to the quadratic function approximation, the constants a, b, c
In calculating , calculation processing for solving three-dimensional simultaneous equations is included. By eliminating this arithmetic processing, the CPU
Another function approximation method that can reduce the load will now be described with reference to FIG.

The function approximation method shown in FIG.
θpmax is the crank angle corresponding to the intersection (maximum value) of a straight line connecting whichever smaller value of
That is. θp obtained by this approximation method
Depending on the magnitude relationship between Pk-s and Pk+1, the following equations (3), (4), and (5) are obtained.

When Pk-s<Pk++, Here, When Pk-t > Pk-z, Here, Pk-1+ Pk+t (i.e., l Pk-1-Pk
+, I≦ε), θpmax θk (5) According to such symmetric two-line approximation, the value of θpmax can be determined with high accuracy while reducing the calculation processing time.

〔Effect of the invention〕

As explained above, according to the present invention, the timing of occurrence of the maximum combustion pressure can be detected with high accuracy without increasing the combustion pressure detection interval, thereby improving the accuracy of ignition timing feedback control. This has the effect of improving the efficiency of the internal combustion engine.

[Brief explanation of drawings]

Fig. 1 is a schematic configuration diagram of an embodiment to which the present invention is applied, Fig. 2 is a diagram illustrating a method for determining the maximum combustion pressure generation timing by quadratic function approximation, and Fig. 3 is a diagram showing two symmetrical lines. FIG. 3 is a diagram for explaining a method of determining the maximum combustion pressure generation timing by approximation. 20... Maximum combustion pressure generation timing detection device 21... Crank angle detection section 22... Combustion pressure detection section

Claims (1)

[Claims] The combustion pressure of the internal combustion engine is detected at every predetermined crank angle pitch, and based on the maximum value of the detected combustion pressure value in a certain period and the detected values at the crank angle pitches before and after that, the combustion pressure for the crank angle in that period is calculated. 1. A method for detecting the timing of maximum combustion pressure in an internal combustion engine, characterized by approximating the change as a function and determining the crank angle corresponding to the maximum value of the approximation function as the timing of maximum combustion pressure.