JPH02204662A - Combustion controller for spark-ignition internal combustion engine - Google Patents

Abstract

PURPOSE:To obviate the occurrence of knocking by judging a combustion state from a direct phenomenon of combustion such as a heat generating rate or a physical quantity being correlated with this heat generating rate, and making it go hand in hand with ignition timing control. CONSTITUTION:An electronic control unit 11 operates a changed state of heat generating rate on the basis of each signal out of a cylinder internal pressure sensor 4 and a crank angle sensor 8, comparing this changed state with that just before knocking occurrence being found and stored by tests or the like in advance, and if it is in a state of being just before the knocking occurrence, a proper timing delay of ignition timing is performed, and optimum combustion control takes place within an unknocking range. In parallel with this combustion control, a knocking state is monitored by a G sensor, and when the knocking occurrence is actually detected, the combustion control based on the heat generating rate is interrupted, and the ignition timing is quickly delayed as much as the specified value. Thus an engine is protectable at a high level from the knocking.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Utilization Public Expenditure> The present invention relates to a combustion control device that maintains optimal combustion conditions in a spark-ignition internal combustion engine and quickly eliminates knocking when it occurs.

<Prior Art> In normal combustion in a spark-ignition internal combustion engine (hereinafter simply referred to as the engine), a part of the air-fuel mixture is ignited by a spark from a spark plug to generate a flame, and the flame further ignites the air-fuel mixture. Proceeds by propagating within. However, when the engine is in a knocking state due to over-advancement of the ignition timing, the unburnt part of the air-fuel mixture during combustion will self-ignite without waiting for flame propagation due to the temperature rise due to adiabatic compression, resulting in combustion. . Since this combustion occurs rapidly, pressure and temperature rise rapidly within the combustion chamber, and shock waves are generated, causing mechanical vibrations in various parts of the engine and overheating and melting of spark plugs, pistons, etc. Therefore, knocking is one of the most harmful phenomena for engines, and efforts are being made to prevent it from occurring by controlling the ignition timing (retarding the ignition timing).

However, on the other hand, the ignition timing that brings out the maximum torque from the engine, the so-called MBT (Mini-Uwa 5P)
ark Advance for Be5t
Torque) is located near the ignition timing that causes knocking, as is well known. Therefore, if the advance angle is increased to increase the torque, the frequency of knocking will increase, and if the advance angle is decreased to suppress knocking, the torque will decrease.

Therefore, in conventional engines, a knock sensor (G sensor), which is a vibration acceleration detection means, is attached to the cylinder block etc., and by detecting the vibration acceleration of the engine due to knocking, the ignition is activated to suppress the occurrence of knocking while extracting the maximum torque. Timing control (advance and retard) was performed. The specific control procedure is to first advance the ignition timing gradually, then retard it by a predetermined amount the moment knocking occurs, and then advance it until knocking occurs again. This is repeated all the time while the engine is running.

<Problems to be Solved by the Invention> The conventional method of suppressing the occurrence of knocking by detecting the vibration acceleration of the engine has the following problems.

Since the ignition timing is always advanced unless actual knocking occurs, instantaneous knocking inevitably occurs at certain intervals, which is a problem from the standpoint of engine protection. Furthermore, in order to reduce the frequency of instantaneous knocking, it is necessary to increase the amount of retardation when knocking occurs, and improvements have been desired from the standpoint of performance as well.

The present invention was made in view of the above situation, and it extracts high torque from the engine while preventing knocking.
It is an object of the present invention to provide a combustion control device that can quickly bring knocking under control when knocking actually occurs.

Means for Solving the Problems> The inventors of the present invention have researched methods for reliably preventing knocking while extracting maximum torque from the engine, and have conducted various experiments. discovered. In other words, near the knocking generation conditions, the combustion rate increases even though no knocking occurs, and as shown in Figure 3(a), the change in heat release rate (indicated by the dashed line) at this time is different from the normal one. During combustion (
(shown by the broken line). The reason for this can be considered as follows.

A chemical reaction during normal combustion is carried out through the following stages: a first peroxide reaction, a second cold flame reaction (formalde and de reaction), and a third hot flame reaction. Among these stages, the third stage is the hot flame reaction, which shows an explosive reaction.In the peroxide reaction and cold flame reaction, hydrocarbons in the fuel first react with high-energy substances such as formaldehyde, OH, HO, etc. It is a precursor reaction that is decomposed into free radicals.

Near knocking conditions, the first and second stage precursor reactions are progressing in the unburned region of the combustion chamber due to high pressure and high temperature, and the chemical activation occurs with more high-energy free radicals than usual. The situation is as follows. Therefore, when the flame front reaches there, a hot flame reaction occurs immediately without the delay required for the precursor reaction, increasing the flame speed and thus the heat release rate.

From these facts, the inventors found the following. That is, if changes in the heat release rate can be detected by some means, it becomes possible to detect a situation on the verge of knocking, and by retarding the ignition timing at that point, knocking can be prevented. Since knocking does not actually occur, the amount of retardation required at this time is smaller than in the conventional system, and it is possible to always set the ignition timing close to the MBT.

However, even if the so-called predictive control described above is performed, knocking may actually occur if the operating conditions change dramatically, such as when a sudden load is applied to the engine. In the case of a method that calculates the situation on the verge of knocking based on changes in the heat release rate, the on-board control device takes time to process the calculations, and has the disadvantage that it cannot quickly respond to sudden knocking. there were.

This VJ was completed based on the above knowledge, and its purpose is to obtain high torque while preventing knocking, while also quickly dealing with sudden knocking to ensure smooth operation. The goal is to realize the following.

In order to solve this problem, the present invention calculates the heat release rate or the state of change of the physical quantity correlated with the heat release rate from the combustion physical quantity detected by the combustion physical quantity detection means,
By comparing this with a value determined in advance, the combustion state is judged and the combustion is performed to obtain the optimum combustion state *JFIIJ
The present invention proposes a combustion control lid characterized in that it determines a knocking state from the detection result of the vibration acceleration detection means and performs combustion control to avoid this knocking state.

Effect> As mentioned above, there is a big difference in the change in heat release rate between the state immediately before knocking and during normal combustion, but physical quantities such as the rate of change in cylinder pressure also change with combustion. The situations are similarly different.

Therefore, in the present invention, first, the heat release rate and the state of change in the above-mentioned physical quantities are calculated from changes in combustion physical quantities such as in-cylinder pressure that are not detected by combustion physical quantity detection means such as in-cylinder pressure sensors, and the state of change is determined in advance by tests etc. Compare it with the state of change just before the knocking occurred. If this is a state immediately before knocking occurs, the ignition timing is appropriately retarded to perform combustion control such that an optimum operating state is obtained within a range where knocking does not occur.

On the other hand, in the present invention, in parallel with this combustion control, the knocking state is also monitored by the vibration acceleration detection means (G sensor). If knocking is actually detected, the combustion control is interrupted and the ignition timing is immediately retarded by a predetermined amount to protect the engine.

Embodiments Two embodiments of the present invention will be specifically described based on the drawings. In both of these embodiments, the combustion state is determined based on the falling region of the heat release rate or in-cylinder pressure change rate (hereinafter represented by #1 generation rate), and the first embodiment The situation is defined as the time required for the heat generation rate to shift, and in the second embodiment, the situation is defined as the amount of falling slope. Since the hardware configurations in these embodiments are the same and the software also has the same parts, the same parts will be explained in the first embodiment.

FIG. 1 schematically shows hardware common to the first and second embodiments, and FIG. 2 shows a flowchart of the common parts of both embodiments. Also, Fig. 3(a), (
bl, (cl each shows a graph, block diagram, and flowchart of the crank angle and heat release rate in the first embodiment, and FIGS. 4(a), (b), (C1 each shows the graph of the crank angle and heat release rate in the second embodiment Graph of crank angle and heat release rate.

A graph and a block diagram of the crank angle and the rate of change in heat release are shown. FIG. 5(aL(b)) shows a block diagram and a step-by-step diagram of the procedure for obtaining the two-disconnection values of the in-cylinder pressure.

FIG. 1 schematically shows an eight-door control system according to an embodiment. In the figure, 1 is a 4-stroke, 4-cylinder gasoline engine for automobiles (hereinafter referred to as engine), and in addition to a spark plug 3, an in-cylinder pressure sensor 4, which is a combustion physical quantity detection means, is attached to the combustion chamber 2 of each cylinder, and the cylinder block A G sensor 6 serving as vibration acceleration detection means is attached to 5. Both the cylinder pressure sensor 4 and the G sensor 6 incorporate piezoelectric elements, and each converts the pressure in the cylinder and the vibration acceleration of the cylinder block 5 into electric charge and outputs the electric charge.

On the other hand, a crank angle sensor 8 is provided adjacent to the flywheel 7, and a signal is output every time the crankshaft of the engine 1 rotates by a unit angle (for example, 1 degree).

The spark plug 3 is connected to the ignition coil 9. power transistor 10
It is connected to an electronic control unit (hereinafter referred to as ECU) 11 via ECU II, and is driven and controlled by this ECU II. The cylinder pressure sensor 4 is connected to the amplifier 12. The G sensor 6 is connected to the ECU II via the multiplexer 13 and the low-pass filter 14, the G sensor 6 is connected to the amplifier 15, and the crank angle sensor 8 is directly connected to the ECU II. Output. A large number of other devices related to the intake system, exhaust gas purification device, etc. are connected to the ECUll, and performs centralized control of the engine 1, but since it would be complicated, a description of their profits and losses will be omitted.

The operation of this embodiment will be described below with reference to FIGS. 2 and 3, but prior to detailed explanation, an outline of the control in this embodiment will be described.

As shown in Fig. 3(a), compared to the heat release rate during normal combustion (shown by the broken line), the heat release rate in the state just before knocking and during knocking (shown by the dashed line and solid line, respectively) is , the way it falls changes significantly. Therefore, by determining the rate of change in the heat release rate in the fall region from the maximum value of the heat release rate to the completion of combustion based on a certain standard, it is possible to detect whether or not the engine is on the verge of knocking. Using this detection result, it is possible to maintain the ignition timing at an optimal value depending on the load condition, gasoline octane number, etc.

In this embodiment, the falling region of the heat release rate, that is, the crank angle from the maximum value to the completion of combustion is defined as the falling time 1.
θ −01 is detected, and this detected value is set as the absolute setting value (
(varies depending on the type of engine).

When the engine 1 rotates in FIG. 3 (cl), the crank angle θ is first detected by the crank angle sensor 8, and the cylinder pressure P of each cylinder is detected by the cylinder pressure sensor 4.

Next, in the ECUll, as shown in Figure 3 (bl),
The heat release rate calculation means 16 calculates the heat release rate dQ using the following procedure.
/d and θ are calculated.

Next, as described below, calculations are performed using each calculation formula and state equation for determining the amount of heat generation dQ and the internal energy increment du.

dQ=G-du+A-P-dV ...(1) du=cv-dT= A'R, dT ...(2) PV=G-R-T ...(3) However, G is the amount of combustion gas, A is the heat equivalent of work, R is the gas constant, Cv is constant volume specific heat, k is the ratio of specific heat, T is absolute temperature.

(11, (21, (from formula 31 -A-R dQ"k-1 dT 10A -P -dV A -, (P-dV+V-dP+ -P-dV-PdV)
K-1 (v'dP+ to 'P'dV) Therefore, the heat release rate (dQ/dθ) is as follows.

dQ A dP
dV-=-(v・-10-P-DingT)...(4)d
Q k-1dθ By the way, the combustion stroke (from top dead center to 50° after top dead center) dV
In dP...<<H, so the above equation can be approximated as follows.

In other words, the heat release rate can be approximated by the value for one break in the cylinder pressure, which is a physical quantity of combustion. Therefore, the rate of change in cylinder pressure may be calculated instead of the heat release rate itself to ensure the speed of calculation control required for real-time control.

In addition, when calculating the heat release rate as described above,
It is desirable to use a filter to cut out high-frequency vibration components caused by knocking, etc.

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 Figure 3 (al). .

Therefore, in this embodiment, a Fourier series type low-pass filter 14 is used. This type of filter has high real-time performance (responsiveness) and is therefore suitable for use in vehicles, but a type using the direct FFT method or spline function method may also be used.

Subsequently, as shown in FIG. 3(b), the crank angle θ, at which the heat generation rate shows the maximum value, is detected in advance by the fall time calculating means 17 in the ECU 9. . and the crank angle θ at which combustion is completed. The fall time (θ1゜.-〇.1
Calculate.

Next, the fall time 1θ, calculated in this way.

. −θ. A determining means 18 in the ECU II compares j with an absolute set value to determine whether or not the engine is on the verge of knocking.

If the state is on the verge of knocking, the next step is to calculate the degree of extra advance (α°) and adjust the ignition timing to α0.
retard. If there is a margin for knocking, calculate the degree of retardation (β°) with respect to the optimal ignition timing and advance the ignition timing by β°. A method may be adopted in which the angle is gradually retarded or advanced each cycle by setting a small constant value.

In addition to the comparison with the above-mentioned absolute set value, methods for determining the combustion state based on the calculated fall time Iθ -61 include the ratio of the heat release rate to the maximum value and the stable heat release rate of the combustion state. The time from a certain crank angle θN1 to a certain crank angle θ8□ in the rising region of is 1ON! The determination may be made based on the ratio to -θNml. Also, the reference time r! in a region where the maximum heat release rate and combustion state are stable. IIθN1-θ
8□1 may be an average value obtained by processing a plurality of data. Furthermore, the determination level of the ratio may be a mapped value that changes depending on the driving conditions.

On the other hand, in this embodiment, knocking is detected by the G sensor 6 in parallel with the ignition timing control described above. and,
If knocking is detected, the combustion control described above is temporarily interrupted and an abnormality determination signal is output as shown in the flowchart of FIG.

When the abnormality determination signal is output, the ignition timing is unconditionally retarded by a predetermined value γ° in this embodiment, but other combustion control means may be driven. For example, if an EGR device is installed, the valve opening time may be increased to
The amount may be increased, or in the case of an engine with an exhaust turbine, the boost pressure may be released by opening a wastegate or the like.

(1 loss 11) In the second embodiment, the maximum negative slope in the falling region of the heat release rate is detected by the rate of change of the heat release rate (d'Q/dθ2), and this detected value is used as described above. The determination is made by comparing with the absolute setting value.
In this embodiment, the above-mentioned detection value can be determined based on the ratio to the maximum positive value of the heat generation rate change rate.

Specifically, first, the rate of change in heat generation rate (d2
Find Q/dθ2) by approximating it by the 21v differential of the cylinder pressure (
Figure 4 (see bl).

That is, from the above-mentioned equation (4), the rate of change in the heat release rate is as shown below.

Here, the combustion stroke (from top dead center to 50° after top dead center) V d
Since P is da (cl), the above equation can be approximated as follows.

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

The apparatus and means for determining the two-disconnect portion of the cylinder pressure are shown in FIG.

That is, the cylinder pressure sensor 4 detects the cylinder pressure Pi sampled once using a sufficiently short sampling period, and the crank angle sensor 8 detects the crank angle θ.

Next, the in-cylinder pressure calculation means 21 reads the in-cylinder pressure P1-8 at the previous sampling at 1 time from the memory 20, and from both P1-1 and the in-cylinder pressure Pi at 1 time,
Calculate the rate of change per unit angle and calculate d P i / da
shall be. Then, the cylinder pressure P1 and its rate of change d P i /da at the i times are stored in the memory 20. After this, the in-cylinder pressure calculation means 22 reads the previous value dP=, /dθ from the memory 20, and calculates dP, -, /da.
The rate of change per unit angle is calculated from both d P i /da at one time and d2Pi/dθ2. d2
Pi/d♂ is stored in memory 20.

It is convenient to approximate the rate of change in the heat release rate using the two-disconnection values of the cylinder pressure obtained in this way, but as described in (5)
It may be determined strictly using a formula.

Then, the maximum value of the heat release rate and the crank angle θ at that time are detected, and the crank angle θ at which combustion is completed is determined. After detecting , the minimum value of the heat release rate change rate is detected within the falling region of the heat release rate. Other configurations and operations are similar to those of the first embodiment.

In the above embodiment, it is preferable that the heat release rate change rate calculating means 19 calculates only the heat release rate change rate within the fall region of the heat release rate described above, since the calculation time can be shortened. In this case, it goes without saying that the minimum value of the heat release rate change rate cannot be compared with the maximum value of the heat release rate change rate that is outside the detection area.

This concludes the explanation of the embodiments, but the present invention is not limited to these embodiments (in the first embodiment and the second embodiment, it is possible to cut off the portion where the heat generation rate changes relatively little). For example, the detection area may be from a crank angle θ5° at which the heat generation rate is 50% of the maximum value of the heat generation rate to a crank angle θ at which the heat generation rate is 10%.

In addition, the time taken up to now to rotate the crank (1
Although we have discussed it as θ−θb+), absolute time (ms, e
The determination may be made using tc). In either case, it is desirable to change the judgment value depending on conditions such as the number of rotations.

In addition, in the above embodiment, the combustion state was determined using the heat release rate or the in-cylinder pressure, but as described above,
The determination may be made using other combustion physical quantities such as a line spectrum.

<Effects of the Invention> As explained above, according to the combustion control device for a spark-ignition internal combustion engine of the present invention, the combustion state can be determined from direct phenomena of combustion such as the heat release rate or physical quantities correlated with the heat release rate. Since the ignition timing is controlled based on the determination, it is possible to perform control that prevents knocking while maintaining good power performance and fuel efficiency. On the other hand, if knocking suddenly occurs, it is detected by the G sensor and combustion control is performed to promptly resolve it, thereby providing a high level of protection for the engine.

[Brief explanation of the drawing]

FIG. 1 is a schematic diagram showing the hardware of the first and second embodiments, and FIG. 2 is a flowchart of common parts of both embodiments. Also, Figure 3 (al, (b), (
C) is a graph, block diagram, and flow chart of the crank angle and heat release rate in the first embodiment, respectively, and FIGS. 4(a), 4(c) are the crank angle and heat release rate in the second embodiment, respectively. They are a graph of the rate of change, a graph of the crank angle and the rate of change in heat release, and a block diagram. and,
FIGS. 5(al) and (b) are block diagrams and flowcharts showing the procedure for obtaining two-disconnection values of cylinder pressure, respectively. In the figures, 1 is the engine, 4 is the cylinder pressure sensor, and 6 is the G Sensors: 8 is a crank angle sensor, 11 is an ECU, 16 is a heat release rate calculation means, 7 is a fall time calculation means, 8 is a discrimination means, 9 is a heat release rate change rate calculation means, 0 is a memory, 1 is cylinder pressure 1 is a cut-off calculation means, and 2 is a cylinder pressure 2rM differential calculation means.

Claims (2)

[Claims] (1) Combustion physical quantity detection means for detecting combustion physical quantities that change with combustion in the combustion chamber of a spark-ignition internal combustion engine, and calculation for calculating changes in heat release rate based on detection signals from this combustion physical quantity detection means. means, storage means for storing changes in the rate of heat generation in the spark-ignition internal combustion engine; vibration acceleration detection means for detecting vibration acceleration of the cylinder section of the spark-ignition internal combustion engine; and heat storage means stored in the storage means. The combustion state of the spark ignition internal combustion engine is determined by comparing the change state of the heat generation rate with the change state of the heat release rate determined by the calculation means, and the combustion control is performed to obtain the optimum combustion state. A combustion control device for a spark-ignition internal combustion engine, comprising: a combustion control device that determines a knocking state from the detection result of the vibration acceleration detection device and performs combustion control to avoid the knocking state. (2) Combustion physical quantity detection means for detecting combustion physical quantities that change with combustion in the combustion chamber of a spark-ignition internal combustion engine; a calculation means for calculating a change state; a storage means for storing a change state of the physical quantity in the spark ignition internal combustion engine; a vibration acceleration detection means for detecting vibration acceleration of a cylinder section of the spark ignition internal combustion engine; The combustion state of the spark ignition internal combustion engine is determined by comparing the state of change in the physical quantity stored in the storage unit with the state of change in the physical quantity determined by the calculation means, and combustion control is performed to obtain the optimum combustion state; A combustion control device for a spark-ignition internal combustion engine, comprising: combustion control means for determining a knocking state from the detection result of the vibration acceleration detecting means and performing combustion control to avoid the knocking state.