JPH0610278Y2 - Cylinder pressure maximum crank angle position detector - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial field of application> The present invention relates to a device for detecting a maximum crank angle position in a cylinder, which is necessary for, for example, feedback control of ignition timing of an internal combustion engine.

<Prior Art> Generally, in an internal combustion engine, when the crank angle position θ _Pmax at which the in-cylinder pressure is maximum is near 15 ° (ATDC15 °) after top dead center, the torque generated by the engine is It is known to be maximum.

Therefore, the crank angle position θ _{Pmax at} which the in-cylinder pressure is maximum is detected, and if θ _Pmax is greater than ATDC 15 °, the ignition timing is advanced, and if θ _Pmax is less than ATDC 15 °, the ignition timing is retarded. Detected θ _Pmax
Based on the above, the ignition timing is feedback-controlled to obtain the maximum torque.

Regarding the detection of the θ _Pmax , in order to improve the detection accuracy, it is sufficient to measure the in-cylinder pressure finely, but in this case, if the microcomputer tries to calculate these detected values, the load on the CPU increases. Therefore, a method for accurately detecting θ _Pmax at a small number of measurement points by using function approximation has been disclosed (see, for example, JP-A-61-68533).

An example of detecting θ _Pmax using such function approximation is as follows.

A plurality of measurement points θ _{1 to} θ ₃ (for example, θ ₁ = ATDC7) near a target value of θ _Pmax (for example, ATDC 15 °) preset so that the cylinder pressure becomes maximum at the crank angle position.
°, θ ₂ = ATDC 15 °, θ ₃ = ATDC 23 °), and in-cylinder pressure values P _{1 to} P detected at these measurement points are determined.
₃ , the θ _Pmax is estimated using a quadratic function approximation.

According to this, θ _Pmax is between the first and last measurement points θ _{1 to} θ
₃ , the in-cylinder pressure value P at each measurement point as shown in FIG.
_{When the in-} cylinder pressure waveform due to ₁ , P ₂ and P ₃ is convex upward, 2
The θ _Pmax can be obtained accurately by the approximation of the next function.

Further, when the theta _Pmax is outside the range of theta ₁ through? _3, wherein P _1, P _2, but cylinder pressure waveform by P ₃ will not be used quadratic function approximation becomes convex downward, in this case P By examining the magnitude relationship between ₁ and P ₃ , θ _Pmax is on the advance side (Fig. 7) from the target value when P ₁ > P ₃ , and on the retard side (P ₁ <P ₃ when the P ₁ <P ₃ 8) can be determined.

<Problems to be solved by the device> However, when the in-cylinder pressure waveform is convex downward as in the conventional case, P
_In the method of discriminating θ _Pmax from the magnitude relationship between ₁ and P _3, the cylinder pressure waveform due to motoring has a relationship of P ₁ > P ₃ as shown in FIG. 9 when misfire occurs. There is a problem that it is not possible to distinguish between the state of misfire and the state of FIG. 7 in which θ _Pmax is on the advance side of the target value.

The present invention has been made in view of the above circumstances, and an in-cylinder pressure maximum crank angle position detection device capable of accurately discriminating the crank angle position of the maximum in-cylinder pressure by the minimum necessary in-cylinder pressure measurement and detecting a misfire state is provided. The purpose is to provide.

<Means for Solving Problems> Therefore, the present invention, as shown in FIG. 1, has means for detecting the crank angle position of the engine and preset so that the in-cylinder pressure becomes maximum at a predetermined crank angle position. To the target crank angle position, the second crank angle position approximately midway between the first crank angle position and the top dead center, and the second crank angle position with respect to the first crank angle position. And in-cylinder pressure detecting means for detecting in-cylinder pressures at three predetermined crank angle positions symmetrical to the third crank angle position, and based on the detected value of the in-cylinder pressure detecting means, In-cylinder pressure waveform shape determining means for determining whether or not the in-cylinder pressure waveform in the range of three crank angle positions is convex, and when the in-cylinder pressure waveform shape determining means determines that it is convex, Based on the cylinder pressure detection value, the secondary function In-cylinder pressure maximum crank angle position estimating means for estimating the in-cylinder pressure maximum crank angle position by numerical approximation, and second and third crank angle positions when it is determined that the in-cylinder pressure waveform shape determining means is not convex upward. The in-cylinder pressure values are compared, and when the second crank angle position side is large, it is determined that the in-cylinder pressure maximum crank angle position is an advance angle, and when the third crank angle position side is large, the in-cylinder pressure maximum crank angle position is Advance / retard determination means for determining a retard angle, and preset in-cylinder pressure detection value of the second crank angle position when the advance / retard determination means determines that the maximum in-cylinder pressure crank angle position is an advance angle. The above-mentioned predetermined value is compared with the predetermined value, and a misfire determination means for determining a misfire when the predetermined value or less is provided.

<Operation> In the above configuration, the in-cylinder pressure value detection crank angle position for determining the in-cylinder pressure maximum crank angle position and the first crank angle position in which the in-cylinder pressure value detection target crank angle position is the maximum in-cylinder pressure There are three crank angle positions, that is, a second crank angle position approximately in the middle between the first crank angle position and the top dead center and a third crank angle position symmetrical to the second crank angle position with respect to the first crank angle position. When the in-cylinder pressure waveform based on the in-cylinder pressure detection values at these three crank angle positions is convex upward, θ _Pmax is accurately estimated by quadratic function approximation. Further, when the in-cylinder pressure waveform is convex downward, based on the magnitude relationship between the in-cylinder pressure value at the second crank angle position and the in-cylinder pressure value at the third crank angle position, the advance angle of θ _Pmax or Determine the retard angle. Then, when the second crank angle position side is large, it is determined as an advance angle. At this time, the latter is smaller depending on whether the in-cylinder pressure is due to combustion or due to motoring. Therefore, the detected value at the second crank angle position is determined. Is compared with a preset slice level, and a misfire is determined when the detected value is equal to or lower than the slice level. In this way, by appropriately setting the in-cylinder pressure detection crank angle position, it is possible to improve the approximation accuracy of the in-cylinder maximum crank angle position by the quadratic function approximation, and to reduce the θ
_Pmax can be accurately discriminated and misfire can be detected.

<Embodiment> An embodiment of the present invention will be described below with reference to the drawings.

FIG. 2 shows a hardware configuration of the present embodiment. In the figure, reference numeral 1 denotes a piezoelectric in-cylinder pressure sensor which is provided as an in-cylinder pressure detecting means in an ignition plug washer portion of an engine body (not shown). The in-cylinder pressure signal is output to the converter 2. A
The / D converter 2 performs A / D conversion of the in-cylinder pressure signal by the input of an A / D conversion timing signal from a microcomputer (hereinafter referred to as a microcomputer) 5 described later.

Reference numeral 3 denotes a crank angle sensor that rotates in synchronization with the crankshaft as crank angle position detecting means. The crank angle sensor 3 generates a reference signal at a predetermined position every time the crankshaft makes two revolutions (720 °), and a unit angle of the crankshaft (for example, 1
A unit signal is output for each .degree.) And is input to the microcomputer 5 via the signal processing circuit 4 including a waveform shaping circuit and the like.

The microcomputer 5 is an I / O interface, CPU, RAM
And a ROM, and based on a signal from the crank angle sensor 3, a target value θ _{0 of the in-} cylinder pressure maximum crank angle position is obtained.
Three preset in-cylinder pressure measurement crank angle positions θ in the vicinity
_The A / D conversion timing signal from _{1 to} θ ₃ is converted into the A / D converter 2
Then, the in-cylinder pressure values P _{1 to} P ₃ are read from the in-cylinder sensor 1. Here, in order to minimize the error due to the approximation of the quadratic function and improve the detection accuracy of the maximum in-cylinder pressure crank angle position, the central crank angle position θ ₂ is set as the target value θ as the three in-cylinder pressure measurement crank angle positions. ₀ (eg ATDC15
Angle), that is, θ ₂ = θ ₁ = ATDC 15 ° is set, and the crank angle position θ ₁ on the top dead center side and a substantially intermediate position between the crank angle position θ ₂ and the top dead center, that is, θ ₁ = ATDC
Set to 7 °, crank angle position θ ₃ on the side opposite to the top dead center
The crank angle position θ with respect to the central crank angle position θ ₂ .
_The position symmetrical to ₁ is set, that is, θ ₃ = ATDC23 °.
Therefore, the crank angle position θ ₂ corresponds to the first crank angle position, the crank angle position θ ₁ corresponds to the second crank angle position, and the crank angle position θ ₃ corresponds to the third crank angle position.

Then, based on the read in-cylinder pressure values P _{1 to} P ₃ , as shown in the flowchart of FIG. 3, when the pressure waveform shape is convex upward, a quadratic function approximation is used to calculate the maximum in-cylinder pressure crank angle. Estimate the position θ _Pmax , while if not convex upward,
From the magnitude relationship between the in-cylinder pressure values P ₁ and P _{3 at} the crank angle position θ ₁ and the crank angle position θ ₃ , the target value θ ₀ (A
It is determined whether θ _Pmax is an advance angle or a retard angle with respect to TDC 15 °) and output to the ignition timing control device 6. When the determination result of θ _Pmax is on the advance side, the in-cylinder pressure value P ₁ at the crank angle position θ ₁ closest to the top dead center is set to the slice level P _SL.
In comparison, when P ₁ <P _SL , misfire is determined. Therefore, the microcomputer 5 corresponds to in-cylinder pressure waveform shape determining means, in-cylinder pressure maximum crank angle position estimating means, advance / retard angle determining means, and misfire determining means. Further, θ ₁ , θ ₂ , and θ ₃ are not limited to the crank angle position of this embodiment, but can be changed according to the setting of the target value.

Next, the cylinder pressure maximum crank angle position detection operation of this embodiment will be described based on the flowchart of FIG.

First, in step (indicated by S in the figure and the same applies hereinafter) 1, when the crank angle signal from the crank angle sensor 3 reaches predetermined crank angle positions θ ₁ , θ ₂ , θ ₃ , the converter 2 outputs a timing signal reads a cylinder pressure signal from the cylinder pressure sensor 1, to obtain a cylinder pressure value P ₁ to P ₃ at each position theta ₁ through? _3.

In step 2, the measured three in-cylinder pressure values P _{1 to} P ₃
Based on the above, it is determined whether the in-cylinder pressure waveform at these three points is convex upward or downward. Here, if 2P ₂ > P ₁ + P ₃ is established, it is convex upward, and the process proceeds to step 3 and P ₁ to P ₁
Cylinder pressure maximum crank angle position θ by quadratic function approximation from _3
Pmax is calculated, and in step 4, the calculated θ _Pmax is output to the ignition timing control device 6.

In this case, in the ignition timing control device 6, this θ _Pmax and the target θ
Ignition timing feedback control similar to that of the prior art is performed in which the ignition timing is advanced or retarded by comparing ₀ with ₀ .

On the other hand, if 2P ₂ > P ₁ + P ₃ is not satisfied in step 2 and it is determined that the in-cylinder pressure waveform due to P _{1 to} P ₃ is convex downward, the process proceeds to step 5 and P ₁ and P ₃ Compare big and small.

If P ₁ <P ₃ in step 5, θ _Pmax is determined to be a retard angle, and a retard angle determination output is generated in step 6. in this case,
In the ignition timing control device 6, for example, a predetermined ignition timing advance process for correcting the advance of a preset constant value ignition timing is executed.

When P ₁ > P ₃ in step 5, the process proceeds to step 7 and the measured value P _{1 at} the crank angle position θ ₁ is compared with the preset slice level P _SL . Here, if P ₁ > P _SL as in the in-cylinder pressure waveform shown by the solid line in FIG.
It is determined that θ _Pmax is in the advanced angle state, the _routine proceeds to step 8 to generate an advanced angle determination output, and the ignition timing control device 6 executes a predetermined ignition timing retarding process for retarding the preset constant value ignition timing. Run.

On the other hand, as shown by the in-cylinder pressure waveform indicated by the broken line in FIG. 4, P ₁ ≦ P
If it is _SL , misfire is determined and the process proceeds to step 9 to generate a misfire determination output, and the ignition timing control device 6 executes predetermined ignition timing processing at the time of misfire.

In this way, the advanced state (FIG. 7) and the misfire state (FIG. 9) of θ _{Pmax which} cannot be determined only by the measured values P _{1 to} P _{3 of} the predetermined crank angle positions θ _{1 to} θ ₃ are set. It can be accurately determined. In addition, near the maximum value of the cylinder pressure waveform,
Strictly speaking, a higher-order curve approximation is not necessarily required, and a higher-order curve approximation is required. When this is estimated by a quadratic function approximation, the cylinder pressure maximum crank angle position θ _{Pmax deviates} from the central detected crank angle position θ _2. Since the approximation error becomes larger, the three in-cylinder pressure detection crank angle positions are set to have the center coincident with the control target value and both ends symmetrically with respect to the center position, as in the present embodiment. By doing so, the approximation error due to the quadratic function approximation can be reduced. In addition, it is experimentally known that, under the lean limit of the air-fuel mixture, as shown in A of FIG. 10, the in-cylinder pressure waveform shows that the in-cylinder pressure drops after passing through the top dead center and then rises. In consideration of such an in-cylinder pressure waveform, the in-cylinder pressure detection crank angle position θ ₁ is set approximately at an intermediate position between the top dead center and the center crank angle position θ ₂ to maximize the in-cylinder pressure maximum crank angle. It is possible to further improve the approximation accuracy of the position θ _Pmax .
In FIG. 10, B shows a cylinder pressure waveform of normal combustion, and C shows
Shows a cylinder pressure waveform at the time of misfire.

According to the present embodiment from the above, the advance angle of theta _Pmax minimum required cylinder pressure rate measurement, it is possible to determine the respective states of retarding and misfire, theta _Pmax target value θ _{0 (=} ATDC15 °) When it is in the vicinity, the position can be accurately estimated, and the accuracy of the ignition timing feedback control can be improved.

Further, in order to reliably perform A / D conversion of the signal from the in-cylinder pressure sensor 1 at the time of high engine speed, it is desirable to widen the in-cylinder pressure detection interval to some extent. On the other hand, MTB during normal operation
The range in which the ignition timing is to be controlled by the control is the range of ± 10 ° of the ignition timing set by the rotation and the load. From this, it is desired to bring the A / D conversion interval closer to 10 ° in crank angle, but if the A / D conversion interval exceeds 8 °, the detection error of the in-cylinder pressure maximum crank angle position θ _Pmax becomes large. Therefore, if the A / D conversion interval of the signal of the in-cylinder sensor 1 is set to 8 ° as in this embodiment, the reliability of the A / D conversion at the time of high engine speed and the maximum in-cylinder pressure crank angle position θ _Pmax. The detection error can be suppressed at the same time, and the detection accuracy can be further improved.

When the in-cylinder pressure sensor is not the absolute pressure sensor, the in-cylinder pressure value P ₄ at the crank angle position θ ₄ sufficiently far from the top dead center where the in-cylinder pressure is not affected by combustion is used as a reference as shown in FIG. As a result, the misfire determination may be performed by comparing the relative value between the reference in-cylinder pressure value P ₄ and the in-cylinder pressure value P ₁ at the crank angle position θ ₁ with the slice level P _SL ′.

<Effects of the Invention> As described above, according to the present invention, the first crank angle position that matches the target value, the second crank angle position approximately in the middle between the first crank angle position and the top dead center, and Based on the in-cylinder pressure detection values at three predetermined crank angle positions, which are symmetrical to the second crank angle position and the third crank angle position with respect to the first crank angle position, the in-cylinder pressure is approximated by a quadratic function approximation or the magnitude relationship between the measured values. The maximum crank angle position is determined.Furthermore, when the maximum cylinder pressure crank angle position is in the advanced state, the magnitude of the predetermined slice level and the cylinder pressure value near top dead center are compared to determine misfire. Since the above configuration is adopted, the maximum in-cylinder pressure crank angle position can be accurately detected or determined by the minimum necessary in-cylinder pressure measurement, and misfire can be detected. Therefore, the accuracy of feedback control of the ignition timing and the like can be improved, and the output of the engine and the fuel consumption can be further improved.

[Brief description of drawings]

FIG. 1 is a block diagram for explaining the configuration of the present invention, FIG. 2 is a hardware configuration diagram of an embodiment of the present invention, FIG. 3 is a control flowchart of the same embodiment, and FIG. 4 is an embodiment of the same. 5 is an explanatory view of a misfire determination operation of FIG. 5, FIG. 5 is an explanatory view of a misfire determination operation in another embodiment of the present invention, and FIGS. 6 to 9 are in-cylinder pressure waveforms for explaining a conventional θ _Pmax detection operation. FIG. 6 is a diagram showing an example, FIG. 6 shows a case where a function approximation is possible, FIG. 7 shows a case of advance angle state, FIG. 8 shows a case of retard angle state, FIG. 9 shows a case of misfire state, and FIG. It is a figure which shows the example of a cylinder pressure waveform at the time of combustion under a lean limit. 1 ... Cylinder pressure sensor, 2 ... A / D converter 3 ... Crank angle sensor, 4 ... Signal processing circuit 5 ... Microcomputer, 6 ... Ignition timing control device

Claims (1)

[Scope of utility model registration request] 1. A means for detecting a crank angle position of an engine,
A first crank angle position that matches a preset target crank angle position so that the in-cylinder pressure is maximized at a predetermined crank angle position, and a second crank that is a position approximately midway between the first crank angle position and top dead center. In-cylinder pressure detection means for detecting in-cylinder pressure at three predetermined crank angle positions, that is, a third crank angle position symmetrical to the second crank angle position and the first crank angle position, and the in-cylinder pressure. An in-cylinder pressure waveform shape determining means for determining whether or not the in-cylinder pressure waveform in the range from the second crank angle position to the third crank angle position is convex upward based on the detection value of the detecting means; An in-cylinder pressure maximum crank angle position estimating means for estimating an in-cylinder pressure maximum crank angle position by a quadratic function approximation based on the three in-cylinder pressure detection values when the pressure waveform shape determining means determines that the in-cylinder pressure maximum crank angle position is high; Internal pressure waveform shape When it is determined that the means is not convex upward, the magnitudes of the in-cylinder pressure values at the second crank angle position and the third crank angle position are compared, and when the second crank angle position side is large, the in-cylinder pressure maximum crank angle position advances. Angle, and when the third crank angle position side is large, the in-cylinder pressure maximum crank angle position is determined to be a retard angle, and advance / retard angle determination means is used to advance the in-cylinder pressure maximum crank angle position. An in-cylinder pressure provided with misfire determination means for comparing the in-cylinder pressure detection value at the second crank angle position with a preset predetermined value and determining a misfire when the angle is equal to or less than a predetermined value. Maximum crank angle position detector.