JP2826591B2 - Knocking control device for spark ignition internal combustion engine - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a knocking control device for preventing knocking of a spark ignition internal combustion engine.

<Prior Art> In a normal combustion in a spark ignition internal combustion engine (hereinafter simply referred to as an engine), a part of the air-fuel mixture is ignited by sparks provided from a spark plug, and a flame is generated. It progresses by propagating inside. However,
When the engine is knocked due to an over-advanced ignition timing or the like, the air-fuel mixture in the unburned portion during combustion self-ignites without waiting for the propagation of the flame due to a temperature rise due to adiabatic compression or the like, and burns at a time. Since this combustion occurs rapidly, pressure and temperature rise rapidly in the combustion chamber, and a shock wave is generated, thereby causing mechanical vibration of each part of the engine and overheating and melting of the ignition plug, piston and the like. Therefore, as one of the most harmful phenomena for the engine, knocking is controlled by ignition timing control (retardation of ignition timing).

However, on the other hand, ignition timing that can extract the maximum torque from the engine, so-called MBT (Mini-mum Spark Advance for
Best Torque) is close to the ignition timing at which knocking occurs, as is well known. Therefore, if the amount of advance is increased to increase the torque, the frequency of occurrence of knocking increases, and if the amount of advance is reduced to suppress knocking, the torque is reduced.

Therefore, in conventional engines, a knock sensor incorporating a piezoelectric element is attached to a cylinder block or the like, and by detecting the vibration acceleration of the engine due to knocking, ignition timing control (progress) that suppresses the occurrence of knocking while extracting the maximum torque. Angle and retard). As a specific procedure of the control, generally, first, the ignition timing is gradually advanced, a predetermined amount of retard is performed at the moment when knocking occurs, and then the advance is performed until knocking occurs again. This is always repeated during engine operation.

<Problems to be Solved by the Invention> In the conventional method of detecting the vibration acceleration of the engine to suppress the occurrence of knocking, detection is not performed unless a knocking state actually occurs, so that, for example, a state immediately before knocking is detected. I couldn't prevent this. For this reason, instantaneous knocking is unavoidable, and the amount of retardation at the time of knocking must be large, and improvement has been desired from both aspects of engine protection and performance maintenance. Further, there is a case where the knock sensor picks up vibration other than the knocking and the unnecessary retard control is performed, so that improvement of the control accuracy is also a concern.

The present invention has been made in view of the above circumstances, and has as its object to manufacture an engine capable of extracting the maximum torque while completely preventing knocking.

<Means for Solving the Problems> The present inventors have researched a method for reliably preventing knocking while extracting the maximum torque from the engine, and have performed various experiments. Was found. That is, in the vicinity of the knocking occurrence condition, the combustion speed is increased even though knocking does not occur, and as shown in FIG. 1 (a), the change in the heat generation rate (indicated by the dashed line) in this case is the normal combustion. It becomes sharper than time (shown by a broken line). The cause is considered as follows.

The chemical reaction at the time of normal combustion is performed through each stage of a first peroxide reaction, a second cool flame reaction (formaldehyde reaction), and a third hot flame reaction. Show explosive reaction among these stages are hot flame reaction in the third stage, the peroxide reacts with the cold flame reaction in the fuel hydrocarbon First formaldehyde or OH, high energy, such as HO ₂ This is a precursor reaction that is decomposed into free radicals.

In the vicinity of knocking conditions, the first and second stage precursor reactions are proceeding due to high pressure and high temperature in the unburned region in the combustion chamber, and are chemically activated with more free radicals of higher energy than usual. It is in a state of being left. Therefore, when the flame surface reaches there, a thermal flame reaction occurs immediately without delay required for the precursor reaction, and the flame speed and thus 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 of the heat generation rate from the change of the in-cylinder pressure,
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, in order to solve the above-mentioned problems, the present invention provides an in-cylinder pressure detecting means for detecting an in-cylinder pressure that changes with the combustion in a combustion chamber of a spark ignition internal combustion engine, and a detection from the in-cylinder pressure detecting means. Calculating means for calculating the change in the heat release rate based on the signal; storage means for storing the change in the heat release rate in the spark ignition internal combustion engine; and change in the heat release rate stored in the storage means. Combustion control means for determining the combustion state of the spark ignition internal combustion engine by comparing the change in the heat release rate obtained by the calculation means and avoiding the knocking state, and performing combustion control. A knock control device for a spark ignition internal combustion engine characterized by the above feature.

<Operation> The in-cylinder pressure is detected by the in-cylinder pressure detecting means during the operation of the engine. Then, the detection signal is sent to an arithmetic unit to calculate a change state of the heat generation rate, and when the change state becomes equal to a change state immediately before knocking stored in advance, combustion control such as ignition timing retard is performed. Go to prevent knocking.

<Embodiment> Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

FIG. 8 schematically shows the hardware of the control system according to the embodiment. In FIG. 1, reference numeral 1 denotes a four-cycle four-cylinder gasoline engine (hereinafter, referred to as an engine) for an automobile. A combustion chamber (cylinder head) 2 of each cylinder is provided with an in-cylinder pressure sensor 4 as an in-cylinder pressure detecting means in addition to a spark plug 3. Installed. The in-cylinder pressure sensor 4 incorporates a piezoelectric element, converts the pressure in the cylinder into electric charges, and outputs the electric charges. On the other hand, a crank angle sensor 6 is provided adjacent to the flywheel 5, and outputs a signal every time the crankshaft of the engine 1 rotates a unit angle (for example, 1 °).

The ignition plug 3 is connected to an electronic control unit (ECU) 9 via an ignition coil 7 and a power transistor 8, and is driven and controlled by the ECU 9. In-cylinder pressure sensor 4
Is connected via a charge amplifier 10, a multiplexer 11, and a low-pass filter 12, and the crank angle sensor 6 is directly connected to the ECU 9, and outputs signals of the in-cylinder pressure and the crank angle to the ECU 9, respectively. A number of other devices related to the intake system, the exhaust gas purification device, and the like are connected to the ECU 9 to perform centralized control of the engine 1. However, description of these devices is omitted because it is complicated.

First Embodiment FIGS. 1A, 1B and 1C show a first embodiment of the present invention. FIG. 1 (a) is a graph showing the relationship between the crank angle (θ) and the heat release rate (dQ / dθ). FIG. 1 (b) is a block diagram of the control system, and FIG. 4) shows the flow of the control by a flowchart.

As shown in FIG. 1 (a), the heat generation rate immediately before knocking and the heat generation rate during knocking (indicated by a dashed line and a solid line, respectively) are lower than those in normal combustion (indicated by broken lines). The fall has changed significantly.
Therefore, if the change rate of the heat release rate in the fall region from the maximum value of the heat release rate to the completion of combustion is determined based on a certain reference, it is possible to detect whether or not the state is immediately before knocking. Then, by using this detection result, the ignition timing can be kept at an optimum value according to the load state, the octane number of gasoline, and the like.

In the present embodiment, the fall region of the heat release rate, that is, the crank angle from its maximum value to the completion of combustion is detected as a fall time | θ ₁₀₀ −θ ₀ |, and this detected value is set to an absolute set value (engine type). Is determined by comparing with the following.

First, the crank angle sensor 6 detects the crank angle θ, and the in-cylinder pressure sensor 4 detects the in-cylinder pressure P of each cylinder.

Next, in the ECU 9, the heat release rate calculation means 13 calculates the heat release rate dQ / dθ 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.

dQ = G · du + A · P · dV (1) PV = G · R · T (3) where G is the fuel gas amount, A is the heat equivalent of work, R is the gas constant, Gv is the specific heat capacity, 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.

Here, in the combustion stroke (top dead center to 50 ゜ after top dead center) Therefore, the above equation can be approximated as follows.

That is, in the combustion stroke between the crank angle phases, the heat generation rate can be approximated. That is, the heat release rate is the amount of change in the amount of heat per unit time, and is calculated from the compression top dead center to the compression top dead center
When the combustion stroke is a crank angle phase up to ゜, it can be approximated by the first derivative of the in-cylinder pressure. In the combustion stroke, heat is generated and the in-cylinder pressure is in the process of rising, so that both the first derivative of the in-cylinder pressure and the heat generation rate are positive values. Θ ₀ corresponds to the crank angle at which the in-cylinder pressure becomes the maximum value.

As described above, when calculating the heat generation rate, it is desirable to cut a high-frequency vibration component due to knocking or the like with a filter. That is, 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. 1 (a). is there. Therefore, in the present embodiment, the Fourier series low-pass filter 12 is used.
Is used. This type of filter is suitable for in-vehicle use because of its high real-time response (responsiveness), but a type using a direct FFT method or a spline function method may be used.

Subsequently, as shown in FIG. 1 (b), the fall time calculating means 14 in the ECU 9 detects the crank angle θ ₁₀₀ at which the heat release rate has the maximum value and the crank angle θ _{0 at} which the combustion is completed, which is detected in advance. Is calculated based on the fall time | θ ₁₀₀ −θ ₀ |.

Next, the fall time | θ thus calculated
The determination means 15 in the ECU 9 compares ₁₀₀₋ θ ₀ | with, for example, an absolute set value to determine whether or not abnormal combustion has occurred, and outputs a determination signal to various combustion control means. Then, for example, when the calculated fall time | θ ₁₀₀ −θ ₀ | is larger than the absolute set value and there is no possibility of knocking, the operation control for gradually advancing the ignition timing and extracting the maximum torque is continued. And
Conversely, when knocking occurs or is in a state where knocking is likely to occur because the knocking is smaller than the absolute set value, a knocking avoidance signal is sent to various combustion control means. When an electronic ignition timing control device is used as the various combustion control means, knocking is avoided by retarding the ignition timing based on the signal. When an electronic device EGR valve of the EGR device is used, the average valve opening time (duty ratio) is increased to increase the amount of EGR, and furthermore, a wastegate valve is used in a supercharged engine. In this case, it may be opened to release the supercharging pressure.

As a method of determining the combustion state based on the calculated fall time | θ ₁₀₀ −θ ₀ |, in addition to the comparison with the above-described absolute set value, the ratio of the heat release rate to the maximum value and the stability of the combustion state are Crank angle θ _{N1 in} the rising region of the determined heat release rate
Crank angle theta time to _N2 in the | θ _N1 -θ _N2 | may determine a ratio to. The reference time | θ _N1 −θ _N2 | in the region where the maximum value of the heat release rate and the combustion state are stable is
The average value obtained by processing a plurality of data may be used. Further, the determination level of the above ratio varies depending on the operating conditions.
A mapped value may be used.

Second Embodiment FIGS. 2 (a) and 2 (b) show a second embodiment of the present invention.

This is done by cutting off a portion where the change in heat release rate is relatively small immediately after the maximum value of the heat release rate and immediately before the completion of combustion, and for example, a crank angle showing a heat release rate of 90% of the maximum value of the heat release rate. Crank angle θ indicating a heat release rate of 10% of the maximum value from θ ₉₀
Set up to ₁₀ as the detection area and its fall time | θ ₉₀
This is an example in which −θ ₁₀ | is detected to improve the measurement accuracy.

According to this, the fall time | θ ₉₀ −θ ₁₀ |
, The maximum value of the heat release rate and the crank angle θ at that time
_In addition to detecting ₁₀₀ , the maximum heat release rate of 90
% Of the heat release rate and the value of the heat release rate of 10%, and the respective crank angles θ ₉₀ , θ ₁₀ at that time are detected, and the crank angle θ _{100 or more} indicating the maximum value of the heat release rate is detected. The fall time | θ ₉₀ −θ ₁₀ | is calculated. Other configurations and operations are the same as those of the first embodiment.

Third Embodiment FIGS. 3A and 3B show a third embodiment of the present invention.

This is because, from the same point of view as in the second embodiment, the heat generation rate in the latter half of the fall region, for example, the heat generation rate of 50% of the maximum value of the heat generation rate, becomes more prominent in the falling direction of the heat generation rate. This is an example in which a range from the crank angle θ ₅₀ indicating the rate to the crank angle θ ₀ at which combustion is completed is set as a detection region, and the fall time | θ ₅₀ −θ ₀ | is detected.

According to this, the fall time | θ ₅₀ −θ ₀ |
, The maximum value of the heat release rate and the crank angle θ at that time
_In addition to detecting ₁₀₀ , the maximum heat release rate of 50
% And the crank angle θ ₅₀ at that time and the crank angle θ ₀ at which combustion is completed are detected, and the fall time after the crank angle θ ₁₀₀ indicating the maximum value of the heat release rate | θ ₅₀ −θ ₀ | is calculated. Other configurations and operations are the same as those of the first embodiment.

Fourth Embodiment FIGS. 4 (a) and 4 (b) show a fourth embodiment of the present invention.

This indicates that the vicinity of the completion of combustion is cut off, for example, to show a heat release rate of 50% of the maximum value of the heat release rate in order to make the tendency of the heat release rate falling in the third embodiment more remarkable. From the crank angle θ ₅₀ to the crank angle θ ₁₀ indicating a heat generation rate of 10% of the maximum value of the heat generation rate is set as a detection area,
This is an example in which the fall time | θ ₅₀ −θ ₀ | is detected.

According to this, the fall time | θ ₅₀ −θ ₀ |
, The maximum value of the heat release rate and the crank angle θ at that time
_In addition to detecting ₁₀₀ , the maximum heat release rate of 50
% Of the heat release rate and the value of the heat release rate of 10% are detected, and the crank angles θ ₅₀ and θ ₁₀ at that time are detected, and the crank angle θ _{100 or more} indicating the maximum value of the heat release rate is detected. The fall time | θ ₅₀ −θ ₁₀ | is calculated. Other configurations and operations are the same as those of the first embodiment.

Fifth Embodiment FIGS. 5A, 5B and 5C show a fifth embodiment of the present invention.

This is because the maximum negative slope in the falling region of the heat release rate is detected by the change rate of the heat release rate (d ² Q / dθ ² ), and this detected value is compared with the absolute set value as described above. This is an example in which the determination is made by performing the above operation. In the present embodiment, the determination of the detection value can also be made based on the ratio of the rate of change of heat release rate to the positive maximum value.

Specifically, the rate of change of the heat release rate (d ² Q / dθ ² ) is first calculated by the heat release rate change rate calculating means 16 provided in the ECU 9.
Is obtained by approximation by the second derivative of the in-cylinder pressure (see FIG. 5 (b)).

That is, the change rate of the heat generation rate is as follows from the above-described equation (4).

By the way, in the combustion stroke (top dead center to 50 ゜ after top dead center) Therefore, the above equation can be approximated as follows.

That is, the heat generation rate can be approximated by the first order differential value of the in-cylinder pressure, which is a physical quantity of combustion. Therefore, the change rate of the in-cylinder pressure may be calculated instead of the heat generation rate itself, and the speed of the arithmetic control required for the real-time control may be ensured.

The apparatus and means for obtaining the second derivative of the in-cylinder pressure are as shown in FIG.

That is, the in-cylinder pressure Pi sampled at i times by the in-cylinder pressure sensor 4 is detected using a sufficiently short sampling cycle, and the crank angle sensor 6 detects the crank angle θ. Next, the in-cylinder pressure first-order differential calculating means 18
From reading the in-cylinder pressure P _i-1 at the time of the previous sampling one time i times, from both the in-cylinder pressure Pi when P _i-1 and i once, by calculating the rate of change per unit angle dPi / dθ. And i
The in-cylinder pressure Pi at the time of rotation and the rate of change dPi / dθ are stored in the memory 17. Thereafter, the in-cylinder pressure second-order differential calculating means 19 reads the previous dP _i-1 / dθ from the memory 17 and obtains dP _i-1 / dθ and i
The rate of change per unit angle is calculated from both dPi / dθ at the time of rotation to obtain d ² Pi / dθ ² . d ² Pi / dθ ² is stored in the memory 17.

It is convenient to approximate the rate of change of the heat release rate by the second order differential value of the in-cylinder pressure obtained in this way, but it may be strictly obtained by the above-mentioned equation (5).

Then, the maximum value of the heat release rate and the crank angle θ at that time
_After detecting ₁₀₀ and the crank angle θ _{0 at} which combustion is completed, the minimum value of the rate of change of the heat generation rate is detected within the fall range of the heat generation rate. Other configurations and operations are the same as those of the first embodiment.

In the above embodiment, it is preferable that the heat release rate change rate calculating means 16 calculate only the heat release rate change rate in the fall region of the heat release rate, because the calculation time can be reduced. In this case, it is needless to say 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 out of the detection area.

Sixth Embodiment FIGS. 6A, 6B and 6C show a sixth embodiment of the present invention.

This is a further development of the modified example of the fifth embodiment, and is an example in which the detection speed of the rate of change of heat release rate is shortened to the latter half of the fall area of the rate of heat release to increase the calculation speed.

According to this, the heat generation rate change rate arithmetic unit 16A, in addition to detecting the maximum value of the heat generation rate and the crank angle theta ₁₀₀ at that time, 50% of the maximum value of the heat generation rate (or the vicinity ) Is calculated, and the crank angle θ ₅₀ indicating the heat generation rate of 50% of the maximum value of the heat generation rate after the crank angle θ ₁₀₀ indicating the maximum value of the heat generation rate, and indicating the completion of combustion. The crank angle θ ₀ is detected. Next, the rate of change of the heat release rate in the latter half of the fall area of the heat release rate is calculated to detect the minimum value. Other configurations and operations are the same as those of the first embodiment.

Note that this until the time | θ _a -θ _b | have been discussed as the period of the absolute time (ms, etc) may be determined using a. In either case, it is desirable that the determination value be changed for each condition such as the number of rotations.

<Effect of the Invention> As described above, according to the knocking prevention apparatus for a spark ignition internal combustion engine of the present invention, knocking is prevented by determining a combustion state using a heat release rate calculated based on in-cylinder pressure. As a result, there is no need to replace the combustion of the engine with mechanical vibration or intrude noise as in the conventional example, and it is possible to prevent knocking quickly and accurately. In particular, according to the present invention, it is possible to determine whether or not a combustion state is occurring immediately before knocking, so that the occurrence of knocking can be avoided beforehand by combination with the knocking avoiding means. In the embodiment, since the in-cylinder pressure sensor is provided for each cylinder, control accuracy is improved.

[Brief description of the drawings]

FIG. 1 relates to a first embodiment of a knocking control device for a spark ignition internal combustion engine according to the present invention. FIG. 1 (a) is a graph showing a relationship between a crank angle and a heat generation rate, and FIG. 1 (b) is a block diagram. FIG. 3C is a flowchart. FIGS. 2, 3, and 4 relate to second, third, and fourth embodiments of the present invention, respectively. FIG. 2 (a) is a graph showing the relationship between the crank angle and the heat release rate. Each figure (b) is a block diagram. 5 and 6 relate to the fifth and sixth embodiments of the present invention. FIG. 5 (a) is a graph showing the relationship between the crank angle and the heat release rate, and FIG. Is a graph showing the relationship between the crank angle and the rate of change of the heat release rate, and each figure (c) is a block diagram. FIG. 7A is a block diagram for obtaining the second order differential value of the in-cylinder pressure, and FIG. 7B is a flowchart showing the procedure. FIG. 8 is a simplified diagram showing the hardware of the control system in the above embodiment. In the figure, 1 is an engine, 4 is an in-cylinder pressure sensor, 6 is a crank angle sensor, 9 is an ECU, 10 is a charge amplifier, 11 is a multiplexer, 12 is a low-pass filter, 13 is a heat generation rate calculation means, and 14 is a fall time. Computing means, 15 means for discriminating means, 16 means for calculating the rate of change in heat release rate, 17 means a memory, 18 means first-order differential calculating means for in-cylinder pressure, and 19 means second-order differential calculating means for in-cylinder pressure.

──────────────────────────────────────────────────続 き Continued on the front page (72) Hiromitsu Ando 5-33-8 Shiba, Minato-ku, Tokyo Inside Mitsubishi Motors Corporation (72) Daisuke Mibayashi 5-33-8 Shiba, Minato-ku, Tokyo No. Mitsubishi Motors Corporation (56) References JP-A-56-54965 (JP, A) JP-A-62-150056 (JP, A) JP-A-55-148937 (JP, A) JP-A-5959 JP-A-136543 (JP, A) JP-A-63-239339 (JP, A) JP-A-63-182278 (JP, U) JP-A-1-66451 (JP, U) (58) Fields investigated (Int. . ⁶ , DB name) F02D 45/00 F02P 5/15

Claims (1)

(57) [Claims] An in-cylinder pressure detecting means for detecting an in-cylinder pressure that changes with combustion in a combustion chamber of a spark ignition internal combustion engine, and a change in heat generation rate is calculated based on a detection signal from the in-cylinder pressure detecting means. Calculating means for storing the change in the heat release rate in the spark ignition internal combustion engine; and the change in the heat release rate stored in the storage means and the change in the heat release rate obtained by the calculation means. Combustion control means for determining the combustion state of the spark ignition internal combustion engine by comparing the state with the situation and performing a combustion control in order to avoid the knocking state; and knocking control of the spark ignition internal combustion engine. apparatus.