JPH0792414B2 - Knocking detection device for internal combustion engine - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an internal combustion engine knocking detection device, and more particularly, to an improved knocking detection method, which uses a cylinder pressure change waveform to determine a crank cycle of each cycle. The present invention relates to a knocking detection device that calculates heat generation with respect to a corner, obtains a ratio of heat generation due to normal combustion and heat generation due to knocking, and determines the strength of knock by this value.

(Prior Art) Since electronic control technology has been extensively used for controlling vehicles and engines, various approaches to knocking have been made. In addition to improving the gas flow and gas flow and increasing the octane number of fuel, the ignition timing is advanced to the limit where slight knocking occurs to the extent that human ears do not feel it depending on the running condition. In this way, knocking control technology, which attempts to obtain the best fuel economy and power performance for each condition regardless of differences in fuel properties and changes in the required octane number of the engine over time, has also come to be used in mass production. Is coming. Recently, the knocking control technology has been applied to each cylinder of a six-cylinder engine. In addition, on-board
Knocking detection and quantification technology are important in knocking control.

Knocking detection methods that can be installed in vehicles for automobiles are classified according to the physical quantity to be detected, and there are various methods such as cylinder pressure, engine vibration, combustion light, knocking sound, and ion current in cylinder.

As a typical conventional knocking detection device for an internal combustion engine, there is one described in “Automotive Technology” 1986 Vol.40 NO11. In this device, an in-cylinder pressure sensor is attached to the spark plug, a high-frequency component near the knocking frequency is detected from the combustion chamber pressure change waveform based on the output of the in-cylinder pressure sensor, and its vibration strength is quantified and statistically processed. The knocking level is decided.

(Problems to be Solved by the Invention) However, in such a conventional knocking detection device for an internal combustion engine, the vibration detected by the in-cylinder pressure sensor is affected by the mounting position, sensor type, sensor type, and detection cylinder. However, it is necessary to adapt the knock detection logic for each engine model, which causes an increase in man-hours and cost, and there is a problem that the detection accuracy is deteriorated when the logic is not sufficiently adapted.

In addition, the in-cylinder pressure sensor used in the conventional knocking detection method is highly effective in that no special processing is required for the engine, but in addition to combustion pressure, vibration of the engine body and mechanical vibration due to rotation Since it also includes, the method using the high frequency signal component obtained from the sensor output has a difficulty in separating the vibration component that becomes noise.
There is a problem that the regular knock component cannot be detected accurately and the detection accuracy is not sufficient.

For example, at high rotations, high-frequency vibration components increase, and it becomes difficult to separate a particular knock component.

(Object of the invention) Therefore, the present invention calculates heat generation for a crank angle for each cycle from a pressure change waveform obtained by cutting a high frequency component of the combustion chamber pressure detected by a sensor, for example, heat generation due to normal combustion and heat due to knocking. By taking the generation ratio and determining the strength of the knock based on this value, the number of man-hours and costs can be reduced without changing the logic regardless of the engine type and the individual difference of the sensor output, and the detection accuracy can be improved. The purpose is to improve.

(Means for Solving the Problems) In order to achieve the above object, the knocking detection device for an internal combustion engine according to the present invention, as shown in the basic conceptual diagram of FIG. 1, shows a combustion pressure or a signal that changes in proportion to the combustion pressure. A pressure detecting means a for outputting, a removing means b for removing a predetermined high frequency component from the output to the pressure detecting means a, an operating state detecting means c for detecting an operating state of the engine, and a crank for detecting a crank angle of the engine. Angle detecting means d and pressure detecting means a
Total heat calculation means e for calculating total heat generation for a crank angle during one cycle from a predetermined calculation processing start timing based on the pressure change waveform from which the high-frequency component of the combustion pressure detected in step S1 and the operating state of the engine have been removed; A start timing setting means f for setting the start timing of the heat generation calculation processing performed by the total heat calculation means e to a predetermined timing later than the ignition timing of the cycle, and a start point for specifying the start point of heat generation due to knocking in one cycle. Identification means g
Knock heat calculation means h for calculating heat generation due to knocking in one cycle, and for calculating a ratio of heat generation due to knocking with one or more of heat generation due to normal combustion or total heat generation during one cycle , And knock intensity determining means i for determining the intensity of knocking based on this ratio.

(Operation) In the present invention, the heat generation for the crank angle for each cycle is calculated from the pressure change waveform obtained by cutting the high frequency component of the combustion chamber pressure detected by the pressure detection means. in this case,
The heat generation calculation process is started at least at a timing later than the ignition timing of the cycle. Then, the ratio of heat generation due to normal combustion (or total heat generation may be used) and heat generation due to knocking is obtained, and the knock strength is determined based on this ratio.

Therefore, unlike the conventional method of digitizing vibration intensity, it is based on the change in heat generation with respect to the crank angle, so it does not require logic changes regardless of the engine model and sensor output differences. It is possible to detect knocking with high accuracy.

In addition, when the heat generation is calculated, the adverse effect of noise on the sensor due to the secondary voltage (high-voltage pulse) of the ignition signal is avoided, the calculation accuracy is improved, noise masking is not required, and the burden is reduced, and the processing speed is reduced. Also improves.

(Example) Hereinafter, the present invention will be described with reference to the drawings.

2 to 11 are diagrams showing an embodiment of a knocking detection device for an internal combustion engine according to the present invention, and are diagrams showing an example in which the present invention is applied to a combustion control device.

First, the configuration will be described. FIG. 2 is an overall configuration diagram of the combustion control device, in which 1 is an engine, intake air is supplied from an air cleaner 2 to each cylinder through an intake pipe 3, and fuel is injected by an injector 4 based on an injection signal Si. Is jetted. The air-fuel mixture in the cylinder explodes and burns due to the discharge action of the spark plug 5 based on the secondary voltage of the ignition signal Sp, becomes exhaust gas, and is discharged from the exhaust pipe 6.

The air flow rate Qa drawn into the engine 1 is the air flow meter 7
And is controlled by the throttle valve 8 in the intake pipe 3. The intake negative pressure (boost) in the intake pipe 3 is detected by an intake pressure sensor 9, and the crank angle of the engine 1 is detected by a crank angle sensor (crank angle detecting means) 10. The engine speed N is calculated by counting the output pulses of the crank angle sensor 10.

The oxygen concentration in the exhaust gas is measured by the oxygen sensor 11 provided in the exhaust pipe 6.
The temperature of the cooling water flowing through the water jacket is detected by the water temperature sensor 12. Further, the combustion pressure (in-cylinder pressure) of each cylinder is detected by an in-cylinder pressure sensor (pressure detecting means) 13, and the in-cylinder pressure sensor 13 is connected to the spark plug 5.
It is tightened and fixed as a washer. Note that the pressure sensor 13 is not limited to the cylinder pressure sensor 13 as long as it generates a signal that changes in proportion to the combustion pressure. For example, a pressure sensitive element may be incorporated in the body of the ignition plug 5.

The air flow meter 7, the intake pressure sensor 9, the crank angle sensor 10, the oxygen sensor 11 and the water temperature sensor 12 constitute an operating state detecting means 14, and outputs from the operating state detecting means 14 and the in-cylinder pressure sensor 13 are control units. Entered in 20. The control unit 20 is composed of a microcomputer and an electronic circuit, calculates a processing value necessary for knocking detection, knock suppression control based on the detection result, and other combustion control (including ignition timing control), and the injection signal Si And the ignition signal Sp are output.

Here, among the functions of the control unit 20, the configuration of the part particularly related to knocking detection and ignition timing control is shown in FIG. In FIG. 3, the output signal of the in-cylinder pressure sensor 13 is input to the high frequency cut filter 21 to remove a predetermined high frequency component, and then A / D converted by the A / D converter 22 and input to the knock intensity calculation circuit 23. To be done. The high frequency component is cut in order to effectively remove the noise component when knocking is detected, and the cutoff frequency for cutting the high frequency component is changed in proportion to the engine speed N as shown in FIG. . In particular,
The engine speed N is calculated based on the output of the crank angle sensor 10 among the outputs of the operating state detecting means 14, and the filter selection circuit 24 selects the optimum cutoff frequency from the characteristics of FIG. 4 based on the calculation result. Then, the fact is output to the high frequency cut filter 21, and the high frequency cut filter 21 cuts the high frequency component of the selected frequency band.

As the high frequency cut filter 21, for example, an analog filter is used. This filter is a combination of elements in which the resistance component has frequency dependence, and by allowing the attenuation of the input signal to have frequency dependence, it transmits or cuts off an arbitrary frequency range.
There are Bessel filters and Butterworth filters. The high frequency cut filter 21 and the filter selection circuit 24 constitute a removing means 25.

Note that the high frequency cut filter 21 is not limited to an analog filter, and as another filter, for example, a filter using Fourier transform may be used. This filter expands the input signal into a Fourier series, where each term is a polynomial corresponding to each frequency, calculates the polynomial in which the terms corresponding to the frequency range to be cut off are deleted, and from this equation It is a filter that transmits or blocks an arbitrary frequency range by reconstructing a signal.

An output signal from the operating state detecting means 14 is also input to the knock strength calculating circuit 23, and the knock strength calculating circuit 23 includes a heat generation calculating portion (corresponding to total heat calculating means) 26 and a knocking heat generation start point detecting portion ( It is composed of a start point specifying means) 27, a knock heat generation calculating section (corresponding to knock heat calculating means) 28, and a knock strength calculating section (corresponding to knock strength determining means) 29. On the other hand, the output signal of the operating state detecting means 14 is further input to the ignition timing control circuit 30, and the ignition timing control circuit 30 sets the ignition timing Adv based on the engine load and the engine speed N and outputs the ignition signal Sp. An ignition unit (not shown) outputs the ignition signal 2 based on this ignition signal Sp.
The next voltage (voltage pulse) is generated to discharge the spark plug 5. The ignition timing set by the ignition timing control circuit 30 is input to a start timing setting circuit 31 (corresponding to start timing setting means), and the start timing setting circuit 31 generates heat at the timing obtained by adding the delay crank angle Td to the ignition timing Adv. It is set as the start timing of the calculation process and output to the heat generation calculation unit 26.

The heat generation calculation unit 26 calculates the total heat generation for the crank angle during one cycle based on the operating state of the engine 1 from the pressure change waveform obtained by removing the high frequency component of the combustion pressure detected by the in-cylinder pressure sensor 13, and this calculation The process is started from the start timing set by the start timing setting circuit 31. The knocking heat generation start point detection unit 27 identifies the starting point of heat generation due to knocking in one cycle. Further, the knock part heat generation calculation unit 28 calculates the heat generation due to knocking in one cycle, and the knock strength calculation unit 29 calculates the ratio between the total heat generation during one cycle and the heat generation due to knocking. The strength of knocking is determined based on the determination result, and the determination result is output to the knock intensity signal output circuit 32. The knock intensity signal output circuit 32 generates a knock intensity signal corresponding to the determination result, outputs it to the ignition timing control circuit 30, and is used for information of knock suppression control. In addition to knocking control, it may be used as input data to a knock intensity input meter as data for detecting knocking, for example.

Next, the operation will be described.

When the engine 1 starts operating, the combustion pressure in the combustion chamber of each cylinder changes, and a peak of the combustion pressure appears every cycle. The calculation of heat generation in this case is calculated as a function of the fuel basic injection amount Tp or the intake negative pressure (boost) or the intake air amount in the knock detection state as shown in FIG. It is started from the point where the value Po, Po = func (Tp or Boost), which has been set, is exceeded and the start timing described later is exceeded.

The calculation of the heat generation amount is executed in step S ₇ described later,
For convenience of explanation, this will be described first, specifically, as follows. Now, as shown in FIG. 6, the cylinder 33
About stroke volume VST, combustion chamber volume V
C, the connecting rod length is CL, and the radius is r, the compression ratio r
c is And the total volume V (θ) at a certain crank angle θ as shown in FIG. It is expressed by Also, as shown in Fig. 7, the polytropic index PN is calculated from the combustion pressure waveforms during the compression stroke from the combustion pressures P ₁ and P ₂ corresponding to 60 ° and 44 ° before TDC and the volumes V ₁ and V _{2 at} that point. Calculate as. Further, in actuality, the combustion pressure P (I) and the volume V (I) for each unit crank angle are sequentially calculated to obtain the total heat generation amount, but the calculation for each unit crank angle is performed by, for example, FIG. P (I), V as shown in a)
In contrast to (I), P (I + 1), V at the next crank angle
It is calculated as (I + 1), and the breakdown of such a pressure change is as shown in FIG. 8 (b): the pressure increase due to combustion at timing t ₁ (corresponding to I) and timing t ₂ (corresponding to I + 1) Both pressure increases due to piston movement are included. Then, calculate one coefficient F _K necessary for calculation of heat generation amount. However, if Cv: constant volume specific heat R: gas constant and the stroke volume at the compression start point is V (1) = VST, the total heat generation Q _A is It is calculated by

Next, the calculation of the heat generation portion due to knocking is performed. The heat generation portion due to knocking is the portion shown by hatching in FIG. In this case, the inflection point of the heat generation change with respect to the crank angle as the starting point of the heat generation part due to knocking is the midpoint between the heat generation start point and the end point, or the inflection point delayed from the compression top dead center (or ignition timing). Is used as the starting point of heat generation by knocking. By determining the knock start point by such a method, the start point can be specified with high accuracy in accordance with the actual combustion state. On the other hand, as the end point of heat generation due to knocking, a point at which heat generation with respect to the crank angle becomes 0 is used. Then, the heat generation amount Q _B due to knocking is
The knock start point and end point are connected by a straight line, and the heat generation portion (hatching portion) that exceeds this straight line is obtained.

When the heat generation amounts Q _A and Q _B are calculated in this way, the knock strength calculation unit 29 then calculates the ratio S between the total heat generation Q _A and the heat generation Q _B due to knocking. The knock strength is determined based on this ratio S.

Next, a program of the knock determination process including the start timing of the heat generation calculation process, which is a feature of the present invention, will be described with reference to the flowchart of FIG. The program shown in the figure is executed in synchronization with a crank angle reference signal (Ref signal).

First, in step S ₁ , the ignition timing Adv is calculated based on the engine load (intake air amount or boost) and the engine speed N.
Is calculated, and the delay crank angle Td is calculated in step S ₂ . As shown in FIG. 11, Td is a delay time in which the ignition delay is predicted in order to set the heat generation calculation processing start timing θ _{1 at} a timing slightly behind the ignition timing Adv, and Td = func (Tp, N) Set with a function expression. Note that Td may be a crank angle or may be set by time. Next, in step S ₃ , the heat generation calculation processing start timing θ ₁ is set by the equation θ ₁ = Adv + Td, and in step S ₄ , the current crank angle θ is read. In steps S ₅ and S ₆ , the crank angle θ is set to θ ₁
And θ ₂ respectively. θ ₂ is the end timing of the calculation process of heat generation (see FIG. 1). θ ₁ ≤ θ ≤ θ ₂
When the proceeds to the step S _7, to end the time being routine otherwise. In step S ₇ , heat generation is calculated by the method as described above, in step S ₈ , the knock intensity is determined from the ratio S, and in step S ₉ , a knock intensity signal corresponding to this is output and the routine ends. .

As described above, in this embodiment, unlike the conventional case where the knocking in which the vibration intensity is digitized is detected, it is based on the change in heat generation with respect to the crank angle,
The knocking can be accurately detected regardless of the engine function, the mounting position of the in-cylinder pressure sensor 13, the individual difference of the sensor output, and the like without requiring the change of the detection logic. Further, since the vibration component is not the detection target, it is not affected by the noise component based on the vibration, and the knocking detection accuracy can be significantly improved as compared with the conventional case. In particular, even if the high-frequency vibration component increases in the high rotation range, the regular knock component can be separated by the heat generation analysis, and the detection accuracy improves. As a result, it is possible to reduce the number of knocking detection steps and the cost.

Further, in order to avoid the adverse effect of noise on the in-cylinder pressure sensor 13 due to the secondary voltage of the ignition signal in the calculation of heat generation, at least after the ignition timing Adv, the delay crank angle Td
Since the calculation is started in consideration of the above, the influence of noise can be removed and the calculation accuracy can be remarkably improved to improve the knocking detection accuracy. Further, this eliminates the need for noise masking and the like, which reduces the load and improves the processing speed.

In the above embodiment, the ratio S is calculated by using the total heat generation Q _A as the denominator, but the present invention is not limited to this. For example, heat generation due to normal combustion (Q _A −Q _B ) is calculated, With this as the denominator The ratio S may be obtained from the following equation.

(Effect) According to the present invention, knocking can be detected accurately regardless of the engine model, the mounting position of the sensor, the individual difference in the sensor output, and the like without requiring a change in the detection logic. It is possible to reduce man-hours and costs.

Further, the adverse effect of ignition noise can be avoided and the calculation accuracy of heat generation can be improved, and the knocking detection accuracy can be significantly improved. Furthermore, it is possible to reduce the burden and improve the processing speed by eliminating the processing such as noise masking.

[Brief description of drawings]

FIG. 1 is a basic conceptual diagram of the present invention, FIGS. 2 to 11 are diagrams showing a first embodiment of a knocking detection device for an internal combustion engine according to the present invention, FIG. 2 is an overall configuration diagram thereof, and FIG. Is a block configuration diagram of its main part, FIG. 4 is a diagram showing characteristics of its cutoff frequency, FIG. 5 is a diagram explaining a starting point of its heat generation calculation, and FIG. 6 is a diagram showing calculation of its compression ratio. FIG. 7 is a diagram showing a part of the combustion pressure waveform, FIG. 8 (a)
(B) is a diagram for explaining the increase of the combustion pressure, FIG. 9 is a diagram for explaining the calculation of the heat generation, FIG. 10 is a flow chart showing the knock intensity judgment program, and FIG. 11 is the combustion pressure waveform. It is a figure which shows the relationship of a calculation process area. 1 ... Engine, 4 ... Injector, 5 ... Spark plug, 7 ... Air flow meter, 9 ... Intake pressure sensor,
10 …… Crank angle sensor, 13 …… Cylinder pressure sensor, 14 ……
Operating state detection means, 20 ... Control unit, 21 ...
… High-frequency cut filter, 22 …… A / D converter, 24 …… Filter selection circuit, 25 …… Remover, 26 …… Heat generation calculator (total heat calculator), 27 …… Knocking heat generation start point detection Section (start point specifying means), 28 ... Knock section heat generation calculation section (knock heat calculation section), 29 ... Knock strength calculation section (knock strength determination section), 30 ... Ignition timing control circuit, 31 ... Start Timing setting circuit (start timing setting means), 32
...... Knock strength signal output circuit.

Claims (1)

[Claims] 1. A) pressure detection means for outputting a combustion pressure or a signal that changes in proportion thereto, b) removal means for removing a predetermined high frequency component from the output of the pressure detection means, and c) operation of the engine. Driving condition detecting means for detecting the state, d) crank angle detecting means for detecting the crank angle of the engine, and e) pressure change waveform and engine operating state in which the high frequency component of the combustion pressure detected by the pressure detecting means is removed. A total heat calculation means for calculating total heat generation for a crank angle in one cycle from a predetermined calculation processing start timing, and f) a start timing of heat generation calculation processing performed by the total heat calculation means as an ignition timing of the cycle. Start timing setting means for setting at a later predetermined time, and g) a start point for specifying a start point of heat generation due to knocking in one cycle. Constant means, h) knock heat calculation means for calculating heat generation due to knocking in one cycle, and i) heat generation due to knocking with one or more of heat generation due to normal combustion or total heat generation during one cycle The knocking detection device for an internal combustion engine, comprising: knocking strength determination means for calculating a ratio of the above, and knocking strength determination means for determining the strength of knocking based on this ratio.