JPH02104971A - Combustion judging method for spark-ignition internal combustion engine - Google Patents

Abstract

PURPOSE:To avoid any occurrence of knocking before it happens by detecting a direct phenomenon of combustion such as buildup time and gradient value in a building-up range of a heat generating rate and thereby judging a combustion state. CONSTITUTION:A crank angle is detected by a crank angle detecting means 1, and cylinder internal pressure is detected by a cylinder internal pressure detecting means 2. A heat generating rate operational means 3 operates a heat generating rate and a variation operational means 4 operates a variation in this heat generating rate respectively. A direct phenomenon of combustion such as buildup time and gradient value or the like in a building-up range of the heat generating rate is detected and thereby a combustion state is judged. Thus, any occurrence of knocking is avoidable before it happens.

Description

Detailed Description of the Invention <Industrial Application> The present invention detects a combustion state in which a spark-ignition internal combustion engine is susceptible to knocking, thereby preventing knocking and determining whether or not a combustion state is possible. Regarding the determination method.

<Prior art> Normal combustion in a spark-ignition internal combustion engine proceeds by igniting a portion of the air-fuel mixture with a spark provided by a spark plug, and the flame propagates within the air-fuel mixture, but knocking occurs. This occurs because part or all of the unburned air-fuel mixture self-ignites and burns all at once without waiting for flame propagation due to the temperature rise due to compression.

This rapid combustion causes a sudden increase in pressure within the combustion chamber and the propagation of pressure waves, causing mechanical vibrations in various parts of the engine, spark plugs, etc.
Knocking can be said to be one of the most harmful phenomena for spark-ignition internal combustion engines because it causes overheating of the pistons, etc.

However, as is well known, the ignition timing that brings out the maximum torque from this spark-ignition internal combustion engine (hereinafter simply referred to as the engine) is close to the conditions that cause knocking.
There is a tendency that the more maximum torque is extracted from the engine, the higher the probability that knocking will occur.

Therefore, in the past, a cylinder pressure sensor and an acceleration sensor were attached to the engine to detect vibrations in the cylinder pressure and mechanical vibrations of the engine that occur due to knocking, and to check whether the engine is operating properly or not, the appropriateness of the ignition timing, etc. The system makes judgments and corrects the ignition timing during operation in order to extract maximum torque from the engine while suppressing the occurrence of knocking.

<Problem to be solved by the invention> The conventional method of detecting cylinder pressure vibrations and engine mechanical vibrations caused by knocking using cylinder pressure sensors and acceleration sensors does not allow the engine to actually generate knocking. Therefore, it has been fundamentally impossible to detect the state on the verge of knocking, prevent knocking, or determine the margin for knocking.

Means for Solving the Problems> The present inventors have researched a method that can reliably prevent knocking while extracting maximum torque from a spark-ignition internal combustion engine, and have conducted various experiments. I discovered a peculiar phenomenon. That is, near knocking conditions, the combustion rate increases even though knocking does not occur, and the change in heat release rate becomes the first.
In the figure, it becomes more rapid near the knocking generation conditions shown by the dashed-dotted line than in the case of normal combustion shown by the solid line. The reason for this is thought to be as follows.

First, the chemical reactions of normal combustion include the first stage peroxide reaction and the second stage cold flame reaction (or formaldehyde reaction).
, and the third stage is a hot flame reaction. Among these stages, it is the third stage that causes an explosive reaction, and in the first and second stages, the hydrocarbons in the fuel become formaldehyde and OH.
, HO2, etc. is a precursor reaction that decomposes into high-energy free radicals.

Here, near the knocking generation conditions, the first ignition occurs in the unburned region in the combustion chamber where the pressure and temperature are on the verge of self-ignition. It is thought that the second stage precursor reaction is progressing, there are many high-energy free radicals, and the state is more chemically activated than usual. For this reason, when the flame front reaches there, the third stage hot flame reaction occurs immediately without the delay required for the precursor reaction, and it is thought that the flame speed and hence the heat release rate increase.

Therefore, the present invention was completed based on the above knowledge, and
The purpose is to provide a combustion determination method that can prevent knocking by detecting a state on the verge of knocking, and can quickly and accurately determine the combustion state in a bench test or the like.

In order to achieve the above object, the combustion determination method for a spark-ignition internal combustion engine according to the present invention calculates a change in heat release rate from a change in cylinder pressure, and determines the combustion state based on the situation in the rising region of this heat release rate. It is characterized by making a judgment.

Effect> When abnormal combustion such as knocking is about to occur, there will be a significant change in the way the heat release rate rises compared to normal combustion.

This is due to the phenomenon that, for example, in a state where knocking is likely to occur, the heat generation rate in the first half of combustion increases due to a precursor reaction, resulting in a short combustion period.

Therefore, the combustion state can be determined by detecting and determining the situation in the rise region of the heat release rate described above based on the time of rise, the amount of slope, or the crank angle phase that produces the maximum value.

Embodiments Hereinafter, embodiments of the combustion determination method for a spark ignition internal combustion engine according to the present invention will be described based on the accompanying drawings.

Figure 1 (al is the heat release rate (dQ/d) of a spark-ignition internal combustion engine
θ) and the crank angle θ. Compared to the heat release rate when there is no sufficient knocking (referred to as non-knocking time), which is shown by the solid line in the same figure, when there is no knocking, which is on the verge of knocking (which is shown by the dashed line in the same figure), The heat generation rate changes greatly depending on how it rises (hereinafter referred to as near the knocking condition) or in the knocking state (hereinafter referred to as knocking) shown by the broken line in the same figure. Therefore, if the rate at which the heat release rate changes in the rising region of the heat release rate from the start of combustion to the maximum value is determined based on a certain standard, it can be determined, for example, whether or not the knock condition is near. It is possible to determine the validity of operating condition settings such as ignition timing, air-fuel ratio settings, and boost pressure.

FIG. 1 shows a first embodiment in which the determination is made based on the slope of the rise of the heat generation rate.

In this example, the maximum value A of the rate of change in the heat release rate near the knocking condition, shown by the dashed line in the figure, is equal to the maximum value A of the rate of change in the heat release rate in the non-knocking state, shown by the solid line in the same figure. Since it is larger than the maximum value B of the rate of change, set a reference value C that is smaller than A and larger than B, and determine whether or not the rate of change of the heat generation rate exceeds this reference value C. When a thermal knock occurs, as shown by the broken line in the same figure, there is a heat generation peak caused by the instantaneous combustion of the gas caused by the knock, so the rate of change in the heat generation rate shows a large value at the moment of knock occurrence. As shown in the same figure, the rate of change in the rate of heat generation changes midway when the knock condition is near, and even in this case, the value exceeds the reference value C, as shown in the figure.

That is, this embodiment is implemented according to the apparatus and means shown in FIG.

First, the crank angle detection means 1 detects the reflux angle θ, and the cylinder pressure detection means 2 detects the cylinder pressure P.

Next, the heat release rate calculating means 3 approximates the heat release rate using the following formula, and the rate of change calculating means 4 approximates the change rate of the heat release rate by the 2# differential value of the cylinder pressure using the following formula. and calculate each.

Amount of heat generation: dQ=G-du+A-P-dV -(
1) -R internal energy increment: du = Cv-dT = -・d
T - (21 to -1 PV = G - R - T ... (3) where, G is the amount of combustion gas, A is the heat equivalent of work, R is the gas constant, Cv is the constant volume specific heat, and k is the specific heat It is a ratio.

(11, (21, (from formula 31 -A-R d Q=-1d T+A ′P ′d VG-A-R
PdV+VdP ・□+A-P-dV -IG-R -7 (PdV+VdP+ -P-dV-PdV) =
, (VdP+k·P-dV) Therefore, the heat generation rate (dQ/dθ) is as follows.

dQ A dP dV-=-(v・
-+ to -P・DingT) dθ k−1dθ Furthermore, the rate of change in the heat release rate is as follows.

Here, combustion stroke (TDC ~ 50° after TDC) dV
Since dP is d# (d61), the above equation can be approximated as follows.

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

The apparatus and means for determining the second order differential of the cylinder pressure are as shown in FIG.

That is, the cylinder pressure detection means 2 detects the cylinder pressure Pi sampled once using a sufficiently short sampling period, and the crank angle detection means 1 detects the crank angle θ.
Detect. Next, the cylinder pressure first-order differential calculation means 6 stores the cylinder pressure P at the time of the previous sampling from the memory 5.
Read out l-1. Calculate the rate of change per unit angle from both p= and cylinder pressure Pi at i times, and calculate d P i /
Let it be dθ. Then, the cylinder pressure Pi and its rate of change d P i /dθ are stored in the memory 5. Thereafter, the cylinder pressure second-order differential calculation means 7 stores the previous value dP, - from the memory 5.

Read /dθ, dP, , /dθ and dPi/ at one time
Calculate the rate of change per unit angle from both dθ
i/dθ2. ! : ii le. d2P I/de21.
t / Stored in Mori 5.

Although it is convenient to approximate the rate of change in the heat release rate using the second derivative of the cylinder pressure obtained in this way, as described above (4)
It may be determined strictly using a formula.

Subsequently, as shown in Figure 2, the rate of change in the heat release rate is the first
It is compared with the reference value C in Figure (b).

If the rate of change in the rate of heat release is less than the standard value C, there is no possibility of knocking and it is sufficient to continue operating control to gradually advance the ignition timing and bring out the maximum torque, but the rate of change in the rate of heat release is the standard. If the value C is exceeded, it can be said that knocking is occurring or that knocking is likely to occur. Therefore, in this embodiment, when the rate of change in the rate of heat release exceeds the reference value C, a knocking avoidance signal is sent to the various combustion control means 9. When an electronic ignition timing control device is used as the various combustion control means 9, knocking is avoided by retarding the ignition timing using the above signal. Also, E
When the electronically controlled EGR valve of the GR device is used, the average valve opening time (duty ratio) is increased to increase EGR,l, and when the wastegate valve of the supercharger is used, this All you have to do is open it to release the boost pressure.

Next, a second embodiment of the present invention will be explained with reference to FIG. 1 (C1) and FIG. (Depending on the timing, it will reach a maximum value as shown by the broken line in the figure)
The crank angle θ0. It was designed to discriminate based on the That is, as shown in FIG. 1(c), the crank angle θ gives the maximum value of the heat generation rate near the knocking condition. Since θ is smaller than the crank angle θ, which gives the maximum heat release rate in the non-knock state, θ. A reference value θ, which is larger and smaller than θ−], is set, and a determination is made based on whether or not the crank angle θM□, which generates the maximum value of the heat release rate, falls below the reference value θ1. This embodiment can be carried out according to the apparatus and procedure shown in FIG. 3, but the difference from the apparatus and procedure shown in FIG. θ. , 8
This is only a comparison with 01 and 01, and other functions and effects are the same as those of the previously described embodiment.

FIG. 1(d) shows a third embodiment of the present invention. In this embodiment, the determination is made based on the rise time θ- of the heat generation rate. Here, the rise time θ
. is the crank angle from the start of combustion to the maximum heat release rate. As shown in FIG. 1 (Td), the rise time M near the knock condition is smaller than the rise time N in the non-knock state.
Set a reference value R smaller than the rise time θ. This is done by comparing it with the . This example is the fourth
Perform according to the equipment and procedures shown in the figure. The difference between the embodiment shown in FIG. 4 and the embodiment shown in FIG. 2 is that the rise time calculation device 11 calculates the rise time θ0,
is the point to be compared with the reference value R. This embodiment also provides the same functions and effects as the embodiment shown in FIG.

<Effects of the Invention> As explained above, according to the combustion determination method for a spark-ignition internal combustion engine of the present invention, direct phenomena of combustion such as the rise time and slope amount in the rise region of the heat release rate can be detected. Since the combustion state is determined by the engine, there is no need to replace the combustion of the engine with mechanical vibrations or the intrusion of noise, which is required in the conventional example. Particularly, according to the present invention, it is possible to determine whether or not the combustion state is on the verge of knocking without knocking, and therefore, in combination with the knocking avoidance means,
It is possible to prevent knocking from occurring.

[Brief explanation of drawings]

Figure 1 (al is a graph showing the relationship between crank angle and heat release rate, Figure 1 (b) (cl) is a graph showing the relationship between crank angle and rate of change in heat release rate, Figure 2 relates to the first embodiment of the present invention;
The same figure (bl is a flowchart showing the procedure, Fig. 3,
FIG. 4 shows the second and third embodiments of the present invention, respectively (11 is a block diagram thereof, each figure (b) is a diagram showing the procedure, and FIG. )
is a block diagram for obtaining the second-order differential value of the cylinder pressure;
bl is a flowchart showing the procedure. In the drawing, 1 is a crank angle detection means, 2 is a cylinder pressure detection means, 3 is a heat release rate rAn means, 4 is a change rate calculation means, 5 is a memory, 6 is a cylinder pressure first order differential calculation means, and 7 is a cylinder Internal pressure two-level differential calculation means. Reference numeral 8 indicates a determination means, 9 indicates various combustion control means, 10 indicates a maximum value occurrence angle detection means, and 11 indicates a rise time calculation means. Figure 1 Figure 1 Figure 2 Section 5 Figure 1

Claims (4)

[Claims] (1) A combustion determination method for a spark-ignition internal combustion engine, which comprises calculating a change in heat release rate from a change in cylinder pressure and determining a combustion state based on a situation in a rising region of the heat release rate. (2) The combustion determination method for a spark-ignition internal combustion engine according to claim 1, wherein the condition of the rising region is the maximum slope of the rise of the heat release rate. (3) The combustion determination method for a spark ignition internal combustion engine as set forth in claim 1, wherein the situation in the rising region is the time at which the heat release rate rises. (4) The combustion determination method for a spark ignition internal combustion engine according to claim 1, wherein the situation in the rising region is the crank angle phase that produces the maximum value of the heat release rate.